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Last Updated :2024/11/06

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Master

Affiliation (Master)

  • Faculty of Science　Institute of Seismology and Volcanology

Affiliation (Master)

  • Faculty of Science　Institute of Seismology and Volcanology

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Profile and Settings

Degree

  • Ph.D.Science Kyoto University（1996/05）

Profile and Settings

  • Name (Japanese)

    Hashimoto

  • Name (Kana)

    Takeshi

  • Name

    200901000069445606

Alternate Names

Achievement

Research Interests

  • 地下構造   crater lake   自然電位   火山   火山ガス   水蒸気   ラマンライダー   分光   熱収支   SO2   geomagnetism   Volcanology   地球電磁気学   火山物理学   

Research Areas

  • Social infrastructure (civil Engineering, architecture, disaster prevention) / Disaster prevention engineering
  • Natural sciences / Solid earth science

Research Experience

  • 2024/04 - Today 文部科学省 科学官（非常勤）
  • 2015/04 - Today Institute of Seismology and Volcanology, Faculty of Science, Hokkaido Univ. Professor
  • 2007/04 - 2015/03 Institute of Seismology and Volcanology, Faculty of Science, Hokkaido University Associate Professor
  • 2006/04 - 2007/03 Institute of Seismology and Volcanology, Faculty of Science, Hokkaido University Associate Professor
  • 2003/03 - 2006/03 Institute of Seismology and Volcanology, Faculty of Science, Hokkaido University Associate Professor
  • 1997/04 - 2003/03 Institute for Geothermal Sciences, Graduate School of Science, Kyoto University Asssistant Professor
  • 1996/04 - 1997/03 Aso Volcanological Laboratory, Faculty of Science, Kyoto University Assistant Professor

Education

  • 1993/04 - 1996/03  Kyoto University  Graduate School of Science  doctoral course
  • 1991/04 - 1993/03  Kyoto University  Graduate School of Science  master course
  • 1987/04 - 1991/03  Kyoto University  Faculty of Science

Awards

  • 2020 日本火山学会 日本火山学会論文賞
     橋本武志・宇津木充・大倉敬宏・神田 径・寺田暁彦・三浦 哲・井口正人 (2019) 非マグマ性の火山活動に伴う消磁及び地盤変動のソースの特微. 火山, 64, 2, 103-119.
  • 1998/11 Society of Geomagnetism and Earth, Planetary and Space Sciences Ohbayashi Prize
     自然電位観測による雲仙普賢岳直下の熱水対流の発達過程の解明

Published Papers

  • K. Aoyama, T. Hashimoto
    Journal of Geophysical Research: Solid Earth 129 (11) 2169-9313 2024/10/29 
    Abstract While the electrical conductivity of smectite‐rich rocks is high, previous studies have only partially revealed its dependence on temperature, salinity, and porosity. This knowledge gap mainly arises from challenges in controlling various experimental conditions when measuring the conductivity of real smectite‐bearing rock samples and quantifying the smectite content. To mimic conductivity measurements under ideal conditions, this study aimed to develop a simulator capable of accurately configuring the conditions to predict the direct‐current conductivity of saturated rocks composed of an aqueous NaCl solution, quartz, and smectite under various temperatures (20°C–200°C), salinities (10−4–5 mol kg−1), porosities (0–1), and smectite fractions (0–1). The simulator reproduced the experimental conductivity measurements from drilled core samples by giving the anisotropy of those components' distribution. In addition, simulations with randomly assigned components revealed that when rocks contain abundant smectite, the bulk conductivity partially decreases with increasing NaCl solution's salinity or volume fraction. These negative slopes were approximated using empirical equations derived from previous studies. Percolation analysis further revealed that when the components are randomly assigned, conductive paths begin to form between the ends of the modeled sample once the sum of the volume fraction of bulk pore and smectite reaches 0.1.
  • Tomohiro Inoue, Takeshi Hashimoto
    Geophysical Journal International 238 (3) 1825 - 1839 0956-540X 2024/07/08 
    SUMMARY Magnetotelluric data are sometimes accompanied by ‘anomalous’ impedance phases ($\phi $xy and $\phi $yx) in the off-diagonal components deviating from the first (0° < $\phi $xy < 90°) or third (−180° < $\phi $yx < −90°) quadrant, especially in long-period bands. This phenomenon is called the phases out-of-quadrant (POQ). The POQ poses a challenge in magnetotelluric modelling because simple 1-D or 2-D models cannot explain it. Previous studies have reported that strong inhomogeneity, anisotropy, or particular 3-D structures, such as the L-shaped or cross-shaped conductors, could explain the POQ. Aside from these models, we have discovered that a slanted columnar conductor also generates the POQ. Our systematic investigation through the synthetic forward modelling of an inclined conductive column with a varying geometry showed that the inclination angle and the column length may affect the POQ appearance. We investigated herein the behaviour of the electric currents around the inclined conductive column embedded in a resistive half-space. We found that the induced electric field in the region with the POQ tends to point in the opposite direction to the surrounding vectors. This result can reasonably explain the inverted phase in long-period bands. Furthermore, we confirmed that current is sucked into one end of the column, but discharged from the other end, suggesting that the column works as a current channel. The localized reverse vectors are associated with the current channelling along the inclined conductor, which generates the POQ. A volcanic conduit within a resistive host rock is one of the typical field examples of such an inclined channel. Our study suggests that the POQ is a helpful clue in imaging the geometry of a volcanic magma plumbing system through magnetotelluric surveys.
  • Takeshi Hashimoto
    Journal of Disaster Research 17 (5) 630 - 638 1881-2473 2022/08/01 [Refereed][Not invited]
     
    Remarkable and continuous geomagnetic field change, suggesting remagnetization at a shallow depth, was detected through repeated geomagnetic field observation of the summit area of Mt. Usu Volcano from 2008 to 2021. Long-term cooling of the remnant magma, that intruded during the 1977–82 eruption, was considered responsible for the remagnetization. A magnetic dipole parallel to the present geomagnetic field well reproduced the observation. The modeled source was located near the Ginnuma crater on the south side of the previously inferred intrusive body beneath the Usu-Shinzan cryptodome. Meanwhile, no magnetic source was detected on the other side of the intrusion, implying asymmetric heat transport paths around the intrusion. Considering previous studies on seismicity, geodetic modeling, and resistivity structure, the magnetic source region is plausibly a high permeability zone through which heat from the intruded magma has been efficiently transported. In other words, the source region can be a key monitoring target for future eruptions as it may be linked to the subsurface magma system.
  • Inoue, T, Hashimoto, T, Tanaka, R, Yamaya, Y
    Earth, Planets and Space 74 114  2022/07 [Refereed][Not invited]
  • Tamura, M, Oka, D, Okazaki, N, Suzuki, K, Hashimoto, T, Mogi, T
    Geothermics 105 102496 - 102496 0375-6505 2022/06 [Refereed][Not invited]
  • Takeshi Hashimoto
    Bulletin of the volcanological society of Japan 67 (4) 489 - 500 2022 [Refereed]
  • Takeshi Hashimoto
    Journal of Geography 130 (6) 771 - 781 2021/12 [Refereed][Not invited]
  • Tanaka R, Yamaya Y, Tamura M, Hashimoto T, Okazaki N, Takahashi R, Mogi T
    Earth, Planets and Space 73 (1) 172  2021/08 [Refereed][Not invited]
     
    Abstract Subvolcanic hydrothermal systems can lead to hydrothermal eruptions as well as unrest phenomena without an eruptive event. Historical eruptions and recent unrest events, including ground inflation, demagnetization, and a gradual decrease in the plume height, at Mt. Tokachidake, central Hokkaido, Japan, are related to such a subvolcanic hydrothermal system. This study investigates the three-dimensional (3-D) resistivity structure of Mt. Tokachidake to image its subvolcanic hydrothermal system. A 3-D inversion of the magnetotelluric data, acquired at 22 sites around the crater area, was performed while accounting for the topography. Our resistivity model was characterized by a high-resistivity layer at a shallow depth (50–100 m) and two conductors near the active crater and dormant crater. The high-resistivity layer was interpreted to be composed of dense lava, which acts as a caprock surrounding the conductor. The high conductivity beneath the active crater can be explained by the presence of hydrothermal fluid in fractured or leached zones within the low-permeability lava layer, as the sources of ground inflation and demagnetization were identified within the conductive zone immediately beneath the resistive layer. The resistivity structure was used to estimate the volume of hydrothermal fluid within the pore space. The minimum volume of hydrothermal fluid beneath the active crater that can explain the resistivity structure was estimated to be 3 × 106 m3. This estimate is comparable to the water volume that was associated with the long runout and highly fluidized lahar in 1926. The resistivity structure and volume of hydrothermal fluid presented in this study can be used as a reference for further numerical simulations, which aim to reveal the mechanisms of recent unrest events and assess the risk of hazards, such as lahar.
  • Matsushima N, Utsugi M, Takakura S, Yamasaki T, Hata M, Hashimoto T, Uyeshima M
    Earth Planets and Space 72 (1) 57  1343-8832 2020/05/07 [Refereed][Not invited]
     
    We investigated the magmatic–hydrothermal system of Aso Volcano, Japan, using broadband magnetotelluric (MT) data. To establish the nature of the shallow crust, a previous resistivity model based on data from 100 measurement sites in and around Aso volcano was revised using data from 9 additional sites near Naka-dake crater, which is located in the central part of the volcano. The components of MT impedance and the tipper vector were used to obtain the resistivity structure by three-dimensional inversion. The resistivity structure shows a subvertical low-resistivity (< 1 Ωm) column-shaped body beneath Naka-dake crater that extends from − 600 m to 10 km below sea level (BSL) and dips steeply to the north-northeast. The position of the upper part of the column is displaced eastward compared with the previous model and does not overlap the position of the presumed magma reservoir inferred previously from seismic and geodetic observations underneath the western side of Naka-dake crater at a depth of 5 km. We interpret this low-resistivity column to be a magmatic–hydrothermal system composed of brine and magma that were transported to Naka-dake crater from the main deep-seated magma reservoir. A horizontal low-resistivity (< 10 Ωm) layer occurs beneath post-caldera cones at the depths of 0–2 km BSL, and this layer extends laterally from the upper part of the low-resistivity column. We interpret this low-resistivity layer as representing a shallow hydrothermal system that has developed around the central column-shaped magmatic–hydrothermal system.[Figure not available: see fulltext.].
  • Hashimoto T, Kanda W, Morita Y, Hayakawa M, Tanaka R, Aoyama H, Uyeshima M
    Journal of Disaster Research 14 (5) 580 - 591 1881-2473 2019/06 [Refereed][Not invited]
     
    The detection capability of various anomalous phenomena preceding volcanic eruptions has considerably progressed as the geophysical monitoring networks have become denser and multi-disciplinary. However, current eruption forecasting techniques, from a practical perspective, still have much scope for improvement because they largely depend on empirical techniques. In the past decade, three-dimensional modeling based on the electromagnetic sounding methods such as magnetotellurics (MT) have become a practical choice, and its recent applications to active volcanic fields has revealed certain common features among volcanoes. Information about the resistivity structure, especially in 'wet' volcanic fields, is useful for the provisional screening of the eruption potential from the viewpoint of the subsurface structure, and, thus, may contribute to the evaluation of eruption imminence in a broad sense. In this study, for evaluation purposes, we present the roles and possible further applications of the subsurface resistivity structure studies by demonstrating the preliminary results and interpretations of an MT survey that we performed in the Kuttara Volcanic Group, northern Japan.
  • Hashimoto T, Utsugi M, Ohkura T, Kanda W, Terada A, Miura S, Iguchi M
    Bull. Volcanol. Soc. Japan 64 (2) 103 - 119 0453-4360 2019/04 [Refereed][Not invited]
  • Inoue T, Hashimoto T
    Geophys. Bull. Hokkaido University 82 (82) 25 - 38 0439-3503 2019/03 [Not refereed][Not invited]
  • Ryo Tanaka, Takeshi Hashimoto, Nobuo Matsushima, Tsuneo Ishido
    Earth, Planets and Space 70 (1) 72  1880-5981 2018/12/01 [Refereed][Not invited]
     
    We investigate a volcanic hydrothermal system using numerical simulations, focusing on change in crater temperature. Both increases and decreases in crater temperature have been observed before phreatic eruptions. We follow the system’s response for up to a decade after hydrothermal fluid flux from the deep part of the system is increased and permeability is reduced at a certain depth in a conduit. Our numerical simulations demonstrate that: (1) changes in crater temperature are controlled by the magnitude of the increase in hydrothermal fluid flux and the degree of permeability reduction (2) significant increases in hydrothermal flux with decreases in permeability induce substantial pressure changes in shallow depths in the edifice and decreases in crater temperature (3) the location of maximum pressure change differs between the mechanisms. The results of this study imply that it is difficult to predict eruptions by crater temperature change alone. One should be as wary of large eruptions when crater temperature decreases as when crater temperature increases. It is possible to clarify the implications of changes in crater temperature with simultaneous observation of ground deformation.[Figure not available: see fulltext.].
  • Hata M, Matsushima N, Takakura S, Utsugi M, Hashimoto T, Uyeshima M
    Journal of Geophysical Research, Solid Earth 123 (8) 6334 - 6346 2169-9313 2018/07 [Refereed][Not invited]
     
    A magma supply system is identified in the upper crust beneath Aso caldera, Japan, appearing as a conductive anomaly via three-dimensional electrical resistivity modeling. Aso caldera contains numerous postcaldera volcanoes, with Naka-dake cone recently experiencing eruptions at the first crater, including an explosive eruption that ejected volcanic ash 11,000 m into the air in October 2016. The magma supply system imaged by the resistivity model consists of four key components: a magma reservoir at ~17 km depth that corresponds to the Conrad discontinuity, a magma-filled crack-propagation zone that extends obliquely from the magma reservoir, another magma reservoir centered at 6 km depth, and an upright crack-intrusion zone at 2–4 km depth. The shape of the conductive anomaly is consistent with the regional stress regime, with the locations of the low-velocity anomalies and a deformation source found beneath the caldera. This anomaly is therefore defined as the magma supply system, which feeds magma to the first crater of the Naka-dake eruptions. The averaged melt fractions of the upper magma reservoir are estimated to be 3%–4% for 89.3 km3 of the reservoir and 96%–99% for 6.3 km3, with resistivity thresholds of <40 and <1 Ωm, respectively. Furthermore, the resistivity model detects three conductive anomalies in Aso caldera that are associated with an aqueous fluid-flow system in the region. The resistivity model also suggests that the resistivity distribution can play an important role in characterizing the stress regime based on the distribution of earthquake clusters in the upper crust beneath the caldera.
  • Hata M, Uyeshima M, Tanaka Y, Hashimoto T, Oshiman N, Yoshimura R
    Journal of Geophysical Reserach, Solid Earth 123 (8) 6397 - 6410 2169-9313 2018/07 [Refereed][Not invited]
     
    The Beppu–Shimabara graben, a tectonically active region comprising a N–S extensional stress field, is characterized by volcanically and seismically active regions in the Southwest Japan subduction zone. We determine the three-dimensional electrical resistivity structure of the graben by inverting network-magnetotelluric data. Our resistivity structure model indicates that the crust beneath the graben is a discontinuous electrically conductive belt that contains four significant conductive anomalies. The four anomalies in the graben are located from the east to west as the following arrangement: in the Hohi volcanic zone centered on Kuju volcano at depths of 0–39 km, at around the northwestern rim of Aso caldera at depths shallower than 7 km, at around the active Naka-dake cone in Aso caldera at depths of 0–17 km, and in the northwestern part of the graben at depths shallower than 7 km. These conductive anomalies in the four locations mainly reflect the effects of various fluids: slab-derived hydrothermal fluid, volcanic thermal fluid, aqueous fluid, and melt. The locations of the anomalies correspond with low seismicity areas in the graben, whereas resistive blocks of the model correspond with high seismicity areas, especially at the southwestern graben, the northeastern graben, and a border between Aso caldera and the Hohi volcanic zone. Our model suggests that the electrical resistivity distribution can contribute to evaluating whether each part of the graben in the regional extensional stress field has a high potential for the earthquake occurrence.
  • Hashimoto T, Terada A, Tanaka R
    Earth Planets Space 70 109  2018/07 [Refereed][Invited]
  • Terada A, Morita Y, Hashimoto T, Mori T, Ohba T, Yaguchi M, Kanda W
    Earth Planets Space 70 64  1880-5981 2018/04 [Refereed][Not invited]
     
    Remote sampling of water from Yugama crater lake at Kusatsu-Shirane volcano, Japan, was performed using a drone. Despite the high altitude of over 2000 m above sea level, our simple method was successful in retrieving a 250 mL sample of lake water. The procedure presented here is easy for any researcher to follow who operates a drone without additional special apparatus. We compare the lake water sampled by drone with that sampled by hand at a site where regular samplings have previously been carried out. Chemical concentrations and stable isotope ratios are largely consistent between the two techniques. As the drone can fly automatically with the aid of navigation by Global Navigation Satellite System (GNSS), it is possible to repeatedly sample lake water from the same location, even when entry to Yugama crater lake is restricted due to the risk of eruption.
  • Hashimoto T, Aoyama H, Koyama H, Morii A, Mishima W, Ogino T, Takahashi R, Okazaki N
    Monthly Chikyu 40 (3) 163 - 169 0387-3498 2018 [Not refereed][Not invited]
  • Akihiko Terada, Takeshi Hashimoto
    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 122 (8) 6108 - 6130 2169-9313 2017/08 [Refereed][Not invited]
     
    We use a numerical model to investigate the factors that control the presence or absence of a hot crater lake at an active volcano. We find that given a suitable pair of parameters (e.g., the enthalpy of subaqueous fumaroles and the ratio of mass flux of the fluid input at the lake bottom to lake surface area), hot crater lakes can be sustained on relatively long timescales. Neither a high rate of precipitation nor an impermeable layer beneath the lake bottom are always necessary for long-term sustainability. The two controlling parameters affect various hydrological properties of crater lakes, including temperature, chemical concentrations, and temporal variations in water levels. In the case of low-temperature crater lakes, increases in flux and enthalpy, which are a common precursor to phreatic or phreatomagmatic eruptions, result in an increase in both temperature and water level. In contrast, a decrease in water level accompanied by a rise in temperature occurs at high-temperature lakes. Furthermore, our model suggests that crater geometry is a key control on water temperature. For lakes with a conical topography, a perturbation in the water level due to trivial nonvolcanic activity, such as low levels of precipitation, can cause persistent increases in water temperature and chemical concentrations, and a decrease in the water level, even though subaqueous fumarolic activity does not change. Such changes in hot crater lakes which are not caused by changes in volcanic activity resemble the volcanic unrest that precedes eruptions. Plain Language Summary The existence of a volcanic crater lake can increase volcanic hazard. Volcanic explosions at crater lakes can be accompanied by tsunamis or base surges. In this study, we develop a numerical model to investigate the factors that control the presence or absence of a hot crater lake at an active volcano. Neither a high rate of precipitation nor an impermeable layer beneath the lake bottom is always necessary for long-term sustainability. Our model predicts two types of a hot crater lake: in the case of low-temperature crater lakes, increases in subaqueous fumarolic activity, which are a common precursor to eruptions, result in an increase in both temperature and water level. In contrast, boiling dry occurs at high-temperature lakes. Furthermore, our model predicts that crater geometry is a key control on water temperature. For lakes with a conical topography, a perturbation in the water level due to trivial nonvolcanic activity, such as low levels of precipitation, can cause persistent increases in water temperature and chemical concentrations. Such changes in hot crater lakes resemble the volcanic unrest that precedes eruptions, referred to as "apparent volcanic unrest."
  • Magnetotelluric survey on Tokachidake volcano -wideband MT survey across the volcano and AMT survey around the crater area-
    Tamura M, Okazaki N, Takahashi R, Hashimoto T, Okuda M, Sugano K, Hayakawa M, Takata M, Hashimoto M, Mishima W
    Conductivity Anomaly Research 16 - 23 2017/03 [Not refereed][Not invited]
  • Yoshiya Usui, Yasuo Ogawa, Koki Aizawa, Wataru Kanda, Takeshi Hashimoto, Takao Koyama, Yusuke Yamaya, Tsuneomi Kagiyama
    GEOPHYSICAL JOURNAL INTERNATIONAL 208 (3) 1359 - 1372 0956-540X 2017/03 [Refereed][Not invited]
     
    Asama Volcano is an andesitic composite volcano and one of the most active volcanoes in Japan. In order to reveal electrical resistivity structure beneath the volcano accurately, we performed a 3-D inversion of dense magnetotelluric survey data. In order to prevent misinterpretation of the subsurface resistivity due to the steep topography around Asama Volcano, we used an unstructured tetrahedral mesh to represent the topography. Furthermore, we reduced the calculation time by transforming the inverse problem from the model space into the data space. Comparison of the new data-space method to the original model-space method showed that the calculation time required to update the model parameters was reduced as a result of the transformation, whereas the resistivity structure obtained remained unchanged. In the subsurface resistivity structure around Asama Volcano that was estimated from the inversion, resistive bodies were discovered to be located under the old eruption centres. In particular, under the 24 ka collapse caldera to the west of the presently active crater, a spherical resistive body was found to exist in isolation. In addition, there was a widespread conductive layer below the resistive surface layer. By comparison with previous hydrological and geochemical studies, the conductive layer was interpreted as being a high-water-content layer and an overlying layer rich in altered clay minerals. Because the western part of the volcanic conduit was considered to be the resistive area, which is inferred to consist of unfractured rocks with lower permeability than their surroundings, it would appear that the area obstructs the westward flow of the hydrothermal fluid beneath the summit, thereby contributing to higher concentrations of SO42- and Cl- in the spring water at the northern and eastern feet as well as the uneven location of a diffuse CO2 anomaly.
  • Ryo Tanaka, Takeshi Hashimoto, Nobuo Matsushima, Tsuneo Ishido
    EARTH PLANETS AND SPACE 69 1880-5981 2017/03 [Refereed][Not invited]
     
    We investigate a volcanic hydrothermal system by using numerical simulation with three key observables as reference: the magnetic total field, vent temperature, and heat flux. We model the shallow hydrothermal system of Mt. Tokachidake, central Hokkaido, Japan, as a case study. At this volcano, continuous demagnetization has been observed since at least 2008, suggesting heat accumulation beneath the active crater area. The surficial thermal manifestation has been waning since 2000. We perform numerical simulations of heat and mass flow within a modeled edifice at various conditions and calculate associated magnetic total field changes due to the thermomagnetic effect. We focus on the system's response for up to a decade after permeability is reduced at a certain depth in the modeled conduit. Our numerical simulations reveal that (1) conduit obstruction (i.e., permeability reduction in the conduit) tends to bring about a decrease in vent temperature and heat flux, as well as heat accumulation below the level of the obstruction, (2) the recorded changes cannot be consistently explained by changing heat supply from depth, and (3) caprock structure plays a key role in controlling the location of heating and pressurization. Although conduit obstruction may be caused by either physical or chemical processes in general, the latter seems more likely in the case of Mt. Tokachidake.
  • Yusuke Yamaya, Toru Mogi, Ryo Honda, Hideaki Hase, Takeshi Hashimoto, Makoto Uyeshima
    GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 18 (2) 735 - 754 1525-2027 2017/02 [Refereed][Not invited]
     
    The Ishikari Lowland on the island of Hokkaido in northeastern Japan is situated at the end of a westward-moving foreland fold-and-thrust belt from the Hidaka collision zone, where the northeastern Japan and Kurile arcs meet. This activity forms a tectonic zone under an east-west compression field in this region. A magnetotelluric resistivity survey was performed to investigate the mechanism for the strain concentration in this region. A three-dimensional (3-D) resistivity inversion showed a conductive thick sedimentary layer and an underlying resistive basement. Remarkable conductors were found in the resistive basement beneath the Ishikari-teichi-toen fault zone (ITFZ) and the Shikotsu caldera. The conductors beneath the ITFZ were interpreted as aqueous fluids that accumulated in the damaged zone in connection with the formation of pull-apart faults and horst. In contrast, the conductor beneath the Shikotsu caldera corresponds to a magmatic fluid path from the upper mantle. These features suggest that the ductile deformation in the upper crust contribute to the strain concentration in this region. The soft thick sediments allow ductile deformations to occur. Furthermore, local fluid-rich zones in the basement cause the crustal strength to be heterogeneous. These thick sediments and local fluids in the basement both contribute to the strain concentration in this region.
  • HATA Maki, MATSUSHIMA Nobuo, TAKAKURA Shinichi, UTSUGI Mitsuru, HASHIMOTO Takeshi, UYESHIMA Makoto
    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN 特定非営利活動法人 日本火山学会 2017 47 - 47 2433-5320 2017
  • Maki Hata, Makoto Uyeshima, Shun Handa, Masashi Shimoizumi, Yoshikazu Tanaka, Takeshi Hashimoto, Tsuneomi Kagiyama, Hisashi Utada, Hiroshi Munekane, Masahiro Ichiki, Kiyoshi Fuji-ta
    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 122 (1) 172 - 190 2169-9313 2017/01 [Refereed][Not invited]
     
    Our 3-D electrical resistivity model clearly detects particular subsurface features for magmatism associated with subduction of the Philippine Sea Plate (PSP) in three regions: a southern and a northern volcanic region, and a nonvolcanic region on the island of Kyushu. We apply 3-D inversion analyses for geomagnetic transfer function data of a short-period band, in combination with results of a previous 3-D model that was determined by using Network-Magnetotelluric response function data of a longer-period band as an initial model in the present inversion to improve resolution at shallow depths; specifically, a two-stage inversion is used instead of a joint inversion. In contrast to the previous model, the presented model clearly reveals a conductive block on the back-arc side of Kirishima volcano at shallow depths of similar to 50km; the block is associated with hydrothermal fluids and hydrothermal alteration zones related to the formation of epithermal gold deposits. A second feature revealed by the model is another conductive block regarded as upwelling fluids, extending from the upper surface of the PSP in the mantle under Kirishima volcano in the southern volcanic region. Third, a resistive crustal layer, which confines the conductive block in the mantle, is distributed beneath the nonvolcanic region. Fourth, our model reveals a significant resistive block, which extends below the continental Moho at the fore-arc side of the volcanic front and extends into the nonvolcanic region in central Kyushu.
  • Koki Aizawa, Hisafumi Asaue, Katsuaki Koike, Shinichi Takakura, Mitsuru Utsugi, Hiroyuki Inoue, Ryokei Yoshimura, Ken'ichi Yamazaki, Shintaro Komatsu, Makoto Uyeshima, Takao Koyama, Wataru Kanda, Taro Shiotani, Nobuo Matsushima, Maki Hata, Tohru Yoshinaga, Kazunari Uchida, Yuko Tsukashima, Azusa Shito, Shiori Fujita, Asuma Wakabayashi, Kaori Tsukamoto, Takeshi Matsushima, Masahiro Miyazaki, Kentaro Kondo, Kanade Takashima, Takeshi Hashimoto, Makoto Tamura, Satoshi Matsumoto, Yusuke Yamashita, Manami Nakamoto, Hiroshi Shimizu
    EARTH PLANETS AND SPACE 69 1880-5981 2017/01 [Refereed][Not invited]
     
    The M-JMA 7.3 Kumamoto earthquake that occurred at 1: 25 JST on April 16, 2016, not only triggered aftershocks in the vicinity of the epicenter, but also triggered earthquakes that were 50-100 km away from the epicenter of the main shock. The active seismicity can be divided into three regions: (1) the vicinity of the main faults, (2) the northern region of Aso volcano (50 km northeast of the mainshock epicenter), and (3) the regions around three volcanoes, Yufu, Tsurumi, and Garan (100 km northeast of the mainshock epicenter). Notably, the zones between these regions are distinctively seismically inactive. The electric resistivity structure estimated from one-dimensional analysis of the 247 broadband (0.005-3000 s) magnetotelluric and telluric observation sites clearly shows that the earthquakes occurred in resistive regions adjacent to conductive zones or resistive-conductive transition zones. In contrast, seismicity is quite low in electrically conductive zones, which are interpreted as regions of connected fluids. We suggest that the series of the earthquakes was induced by a local accumulated stress and/or fluid supply from conductive zones. Because the relationship between the earthquakes and the resistivity structure is consistent with previous studies, seismic hazard assessment generally can be improved by taking into account the resistivity structure. Following on from the 2016 Kumamoto earthquake series, we suggest that there are two zones that have a relatively high potential of earthquake generation along the western extension of the MTL.
  • Koshun Yamaoka, Nobuo Geshi, Takeshi Hashimoto, S. E. Ingebritsen, Teruki Oikawa
    EARTH PLANETS AND SPACE 68 1880-5981 2016/11 [Refereed][Not invited]
  • Maki Hata, Shinichi Takakura, Nobuo Matsushima, Takeshi Hashimoto, Mitsuru Utsugi
    GEOPHYSICAL RESEARCH LETTERS 43 (20) 10720 - 10727 0094-8276 2016/10 [Refereed][Not invited]
     
    At Naka-dake cone, Aso caldera, Japan, volcanic activity is raised cyclically, an example of which was a phreatomagmatic eruption in September 2015. Using a three-dimensional model of electrical resistivity, we identify a magma pathway from a series of northward dipping conductive anomalies in the upper crust beneath the caldera. Our resistivity model was created from magnetotelluric measurements conducted in November-December 2015; thus, it provides the latest information about magma reservoir geometry beneath the caldera. The center of the conductive anomalies shifts from the north of Naka-dake at depths >10km toward Naka-dake, along with a decrease in anomaly depths. The melt fraction is estimated at 13-15% at similar to 2km depth. Moreover, these anomalies are spatially correlated with the locations of earthquake clusters, which are distributed within resistive blocks on the conductive anomalies in the northwest of Naka-dake but distributed at the resistive sides of resistivity boundaries in the northeast.
  • Hiroshi Ichihara, Toru Mogi, Kengo Tanimoto, Yusuke Yamaya, Takeshi Hashimoto, Makoto Uyeshima, Yasuo Ogawa
    GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 17 (4) 1480 - 1491 1525-2027 2016/04 [Refereed][Not invited]
     
    The Hidaka collision zone, where the Kurile and northeastern (NE) Japan arcs collide, provides a useful study area for elucidating the processes of arc-continent evolution and inland earthquakes. To produce an image of the collision structure and elucidate the mechanisms of anomalously deep inland earthquakes such as the 1970 Hidaka earthquake (M6.7), we conducted magnetotelluric observations and generated a three-dimensional resistivity distribution in the southern part of the Hidaka collision zone. The modeled resistivity was characterized by a high resistivity area in the upper crust of the Kurile arc corresponding to metamorphic rocks. The model also showed conductive zones beneath the center of the collision zone. The boundary between the resistive and conductive areas corresponds geometrically to the Hidaka main thrust, which is regarded as the arc-arc boundary. The correspondence supports the collision model that the upper-middle part of crust in the Kurile arc is abducting over the NE Japan arc. The conductive areas were interpreted as fluid-filled zones associated with collision processes and upwelling of dehydrated fluid from the subducting Pacific slab. The fluid flow possibly contributes to over-pressurized conduction that produces deep inland earthquakes. We also observed a significant conductive anomaly beneath the area of Horoman peridotite, which may be related to the uplift of mantle materials to the surface.
  • Preliminary result of MT survey at Usu volcano and Tokachidake volcano, Hokkaido
    Tamura M, Okazaki N, Takahashi R, Oka D, Akita F, Okuda M, Hashimoto T, Sugano K, Mogi T, Yamaya Y, Fujimatsu J, Nagayama H, Michishita T
    Conductivity Anomaly Research 84 - 89 2016/03 [Not refereed][Not invited]
  • Tanaka R, Hashimoto T, Suzuki A
    Geophysical Bulletin of Hokkaido University 北海道大学大学院理学研究院 79 15 - 23 0439-3503 2016/03 [Not refereed][Not invited]
     
    We performed measurements of the magnetic total intensity at Nakamachineshiri crater of Meakandake volcano, eastern Hokkaido, in 2013, 2014 and 2015. Comparing the three campaigns, we found small but systematic magnetic changes suggesting demagnetization at the shallow subsurface of the crater during 2014-2015. We estimated the best-fit demagnetized source as a sphere with magnetic moment of 2×106 Am2 at a depth of 250 m (960 m a.s.l) beneath the crater. We then considered it was brought by thermal demagnetization, and made an order estimation of the heating rate at the source by assuming a simplistic temperature-magnetization relationship. In addition, we assessed the surface heat loss due to discharging fumarolic gas, evaporation and radiation from hot ponds, and geothermal anomalies. Total amount of the surface heat discharge rate was estimated to be in a range from a few to 10-odd MW. This might be comparable or one-order smaller than the heating rate based on the crude estimation from magnetic measurements.
  • Toshiya Mori, Takeshi Hashimoto, Akihiko Terada, Mitsuhiro Yoshimoto, Ryunosuke Kazahaya, Hiroshi Shinohara, Ryo Tanaka
    EARTH PLANETS AND SPACE 68 1880-5981 2016/03 [Refereed][Not invited]
     
    A phreatic eruption of Mt. Ontake, Japan, started abruptly on September 27, 2014, and caused the worst volcanic calamity in recent 70 years in Japan. We conducted volcanic plume surveys using an electric multirotor unmanned aerial vehicle to elucidate the conditions of Mt. Ontake's plume, which is flowing over 3000 m altitude. A plume gas composition, sulfur dioxide flux and thermal image measurements and a particle sampling were carried out using the unmanned aerial vehicle for three field campaigns on November 20 and 21, 2014, and June 2, 2015. Together with the results of manned helicopter and aircraft observations, we revealed that the plume of Mt. Ontake was not directly emitted from the magma but was influenced by hydrothermal system, and observed SO2/H2S molar ratios were decreasing after the eruption. High SO2 flux of > 2000 t/d observed at least until 20 h after the onset of the eruption implies significant input of magmatic gas and the flux quickly decreased to about 130 t/d in 2 months. In contrast, H2S fluxes retrieved using SO2/H2S ratio and SO2 flux showed significantly high level of 700-800 t/d, which continued at least between 2 weeks and 2 months after the eruption. This is a peculiar feature of the 2014 Mt. Ontake eruption. Considering the trends of the flux changes of SO2 and H2S, we presume that majority of SO2 and H2S are supplied, respectively, from high-temperature magmatic fluid of a deep origin and from hydrothermal system. From the point of view of SO2/H2S ratios and fumarolic temperatures, the plume degassing trend after the 2014 eruption is following the similar course as that after the 1979 eruptions, and we speculate the 2014 eruptive activity will cease slowly similar to the 1979 eruption.
  • Tony Hurst, Takeshi Hashimoto, Akihiko Terada
    Volcanic Lakes 307 - 321 2015/01/01 [Refereed][Not invited]
     
    The volume and temperature of a Crater Lake in an active volcano depends on the balance between the input of volcanic fluids and gases, with their thermal energy, and the evaporation and other processes by which the lake loses energy. The general situation is that we can measure the bulk properties of the lake, and want to determine the mass and energy that is entering the bottom of the lake from the volcano. This chapter describes the processes likely to be significantly affecting such a lake, and how to estimate their effect. Evaporation is the dominant cooling process for hot lakes, and we compare proposed equations to select those most suitable for the volcanic lake situation. Several case studies are included to show how heat and energy balance calculations can be used in actual situations.
  • Volcanomagnetic Effects and Phreatic Eruptions
    Hashimoto T
    Conductivity Anomaly Research 75 - 81 2015 [Not refereed][Not invited]
  • Electrical Resistivity Structure Beneath the Kyushu District by Using Geomagnetic Transfer Functions
    Hata, M, M. Uyeshima, S. Handa, M. Shimoizumi, Y. Tanaka, T. Hashimoto, T. Kagiyama, H. Utada, H. Munekane, M. Ichiki, K. Fujita
    Conductivity Anomaly Research 18 - 20 2015 [Not refereed][Not invited]
  • Mishima, W, T. Hashimoto, T. Mogi, T. Moriyama, J. Ohgi, K. Morinaga
    Geophysical Bulletin of Hokkaido University 北海道大学大学院理学研究院 78 (78) 69 - 82 0439-3503 2015 [Not refereed][Not invited]
     
    Regional to subregional-scale anomaly in the rate of geomagnetic secular changes have been observed in eastern Hokkaido. The origin of such anomalous changes has long been discussed. Based on the total field records, some previous studies suspected the piezomagnetic effect is due to stress loading accompanying subducting plate motion as the major cause. We started three-component absolute measurements at eight continuous magnetic stations in 2009, aiming at revealing the mechanisms of the anomaly. This study reports the results of the absolute measurements up to 2014, as well as the continuous total field records. Although we have performed the absolute measurements only twice or three times at each station, it is readily recognized that the rate of secular change with respect to Memambetsu in horizontal and vertical components differs from site to site. Steeper trends near the southern coast are the characteristics similar to the case in the total field. Declination looks more complicated, presumably showing clockwise rotation in the northern area, while anti-clockwise in the south. Considering the compressional stress region of eastern Hokkaido and existence of highly-magnetized rocks in the coastal area, the piezomagnetic effect is still a candidate for these spatiotemporal variations. Based on the available dataset, we conclude that the anomaly in the total field is not brought by the so-called orientation effect, and that there must be such real changes of tens to hundred km scale, whatever the cause is. It should be the next step in the future works to verify the piezomagnetic hypothesis by comparing the three-component rate of change through a numerical simulation.
  • Takeshi Hashimoto, Takao Koyama, Takayuki Kaneko, Takao Ohminato, Takatoshi Yanagisawa, Mitsuhiro Yoshimoto, Eiichi Suzuki
    EXPLORATION GEOPHYSICS 45 (1) 37 - 42 0812-3985 2014/03 [Refereed][Not invited]
     
    Unmanned aerial vehicles (UAVs) have recently received attention in various research fields for their ability to perform measurements, surveillance, and operations in hazardous areas. Our application is volcano surveillance, in which we used an unmanned autonomous helicopter to conduct a dense low-altitude aeromagnetic survey over Tarumae Volcano, northern Japan. In autonomous flight, we demonstrated positioning control with an accuracy of similar to 10 m, which would be difficult for an ordinary crewed vehicle. In contrast to ground-based magnetic measurement, which is highly susceptible to local anomalies, the field gradient in the air with a terrain clearance of 100 to 300 m was fairly small at 1 nT/m. This result suggests that detection of temporal changes of an order of 10 nT may be feasible through a direct comparison of magnetic data between separate surveys by means of such a system, rather than that obtained by upward continuation to a common reduction surface. We assessed the temporal magnetic changes in the air, assuming the same remagnetising source within the volcano that was recently determined through ground surveys. We conclude that these expected temporal changes would reach a detection level in several years through a future survey in the air with the same autonomous vehicle.
  • Hashimoto, T, T. Koyama, T. Ohminato, T. Kaneko, T. Yanagisawa, M. Yoshimoto, E. Suzuki
    Conductivity Anomaly Research CA研究グループ 92 - 99 2014 [Not refereed][Not invited]
  • Koki Aizawa, Takao Koyama, Hideaki Hase, Makoto Uyeshima, Wataru Kanda, Mitsuru Utsugi, Ryokei Yoshimura, Yusuke Yamaya, Takeshi Hashimoto, Ken'ichi Yamazaki, Shintaro Komatsu, Atsushi Watanabe, Koji Miyakawa, Yasuo Ogawa
    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 119 (1) 198 - 215 2169-9313 2014/01 [Refereed][Not invited]
     
    Broadband magnetotelluric (MT) measurements were conducted in 2010 and 2011 in the vicinity of Shinmoe-dake Volcano in the Kirishima volcano group, Japan, where sub-Plinian eruptions took place 3 times during 26-27 January 2011. By combining the new observations with previous MT data, it is found that an anomalous phase in excess of 90 degrees is commonly observed in the northern sector of the Kirishima volcano group. Because the anomalous phase is not explained by 1-D or 2-D structure with isotropic resistivity media, 3-D inversions were performed. By applying small errors to the anomalous phase, we successfully estimated a 3-D resistivity structure that explains not only the normal data but also the anomalous phase data. The final model shows a vertical conductor that is located between a deep-seated conductive body (at a depth greater than 10 km) and a shallow conductive layer. By applying the findings of geophysical and petrological studies of the 2011 sub-Plinian eruptions, we infer that the subvertical conductor represents a zone of hydrothermal aqueous fluids at temperatures over 400 degrees C, in which a magma pathway (interconnected melt) is partially and occasionally formed before magmatic eruptions. To the north of the deep conductor, earthquake swarms occurred from 1968 to 1969, suggesting that these earthquakes were caused by volcanic fluids.
  • Y. Yamaya, P. K. B. Alanis, A. Takeuchi, J. M. Cordon, T. Mogi, T. Hashimoto, Y. Sasai, T. Nagao
    BULLETIN OF VOLCANOLOGY 75 (7) 0258-8900 2013/07 [Refereed][Not invited]
     
    Taal Volcano, located in the southwestern part of Luzon Island, Philippines, has frequently experienced catastrophic eruptions from both the Main Crater on Volcano Island and flank eruptions. These eruptions have been magmatic, phreatomagmatic, and hydrothermal, with the latter implying the existence of a large-scale hydrothermal system beneath the volcano. We conducted an electrical resistivity survey using the magnetotelluric method in order to identify the location and geometry of the hydrothermal reservoir and sealing cap rock. Two-dimensional inversion using the observed data indicates four similar resistivity sections. The structure at shallow depths corresponds to volcanic deposits and an aquifer. Below 1 km, the structure features a relatively resistive zone beneath the main crater surrounded by a conductive shell. We interpreted these to be a large hydrothermal reservoir with an impermeable cap rock sealing it. Recent ground deformation detected by GPS measurements suggests that the hydrothermal reservoir is active. The interpreted cap rock thins just beneath the main crater and could easily be destroyed by an imbalance in the hydrothermal system. We conclude that this hydrothermal reservoir plays a significant role in driving catastrophic eruptions that begin with a hydrothermal explosion at the main crater.
  • Kanda W, Ogawa Y, Takakura S, Koyama T, Hashimoto T, Komori S, Sonoda T, Sato I, Inoue N, Utsugi M
    Conductivity Anomaly Research CA研究グループ 139 - 144 2013 [Not refereed][Not invited]
  • Hashimoto, T, T. Koyama, T. Kaneko, T. Ohminato, T. Yanagisawa, M. Yoshimoto, E. Suzuki
    Conductivity Anomaly Research CA研究グループ 81 - 87 2013 [Not refereed][Not invited]
  • Koki Aizawa, Takao Koyama, Makoto Uyeshima, Hideaki Hase, Takeshi Hashimoto, Wataru Kanda, Ryokei Yoshimura, Mitsuru Utsugi, Yasuo Ogawa, Ken'ichi Yamazaki
    EARTH PLANETS AND SPACE 65 (6) 539 - 550 1343-8832 2013 [Refereed][Not invited]
     
    Three sub-Plinian eruptions took place on 26-27 January 2011 at Shinmoe-dake volcano in the Kirishima volcanic group, Japan. During this event, GPS and tiltmeters detected syn-eruptive ground subsidence approximately 7 km to the WNW of the volcano. Starting in March 2011, we conducted broad-band magnetotelluric (MT) measurements at a site located 5 km NNW of the volcano, beneath which the Shinmoe-dake magma plumbing system may exist. In addition, temperature monitoring of fumaroles and hot-springs near the MT site was initiated in July 2011. Our MT data record changes in apparent resistivity of approximately +/- 5%, along with a +/- 1 degrees. phase change in the off-diagonal component of the impedance tensor (Z(xy) and Z(yx)). Using 1-D inversion, we infer that these slight changes in resistivity took place at relatively shallow depths of only a few hundred meters, at the transition between a near-surface resistive layer and an underlying conductive layer. Resistivity changes observed since March 2012 are correlated with the observed temperature increases around the MT monitoring site. These observations suggest the existence beneath the MT site of pathways which enable volatile escape.
  • Ryo Tanaka, Takeshi Hashimoto
    Earth, Planets and Space 65 (6) 645 - 655 1880-5981 2013 [Refereed][Not invited]
     
    Mount Shinmoe-dake, in the Kirishima volcanic group (in southern Kyushu, Japan), erupted in January 2011. The eruption style was initially phreatomagmatic, and then underwent a series of transitions from sub-plinian explosions to an extrusion of lava from the summit crater. The purpose of the present study is to investigate the cause of such changes in eruption styles, focusing on the conditions for the eruption to be non-explosive and for the lava effusion to cease. To examine the conditions in the conduit and magma chamber, a numerical code is devised, based on the one-dimensional steady flow model of Kozono and Koyaguchi (2010), who modeled a dome-forming eruption. We systematically search for a condition in which the magma would not be fragmented, but the initial volatile content in the magma chamber would remain constant and unchanged. We find that the high magma permeability and/or the high degree of lateral gas escape was needed for the eruption to be effusive, and we estimate the pressure decrement at the cessation of lava extrusion.
  • Kanda, W, T. Yamazaki, Y. Ogawa, T. Hashimoto, K. Aizawa, S. Takakura, T. Koyama, K. Yamada, T. Kobayashi, S. Komori
    Bull. Volcanol. Soc. Japan 特定非営利活動法人 日本火山学会 58 (1) 251 - 267 0453-4360 2013 [Refereed][Not invited]
     
    An audio-frequency magnetotelluric (AMT) survey was conducted at the foot of Sakurajima volcano in November 2007. This survey was carried out within the framework of the 7th National Project for Prediction of Volcano Eruptions. The main objective was to clarify the shallow layers of Sakurajima volcano for better understanding of the volcanic activity. We measured electromagnetic fields at frequencies from 1 to 10400 Hz at 27 locations along only three lines set on the northern, western, and southeastern flanks of the volcano. The three profiles enclosed the summit area where access is prohibited because of frequent explosive vulcanian eruptions. The data quality was generally considered to be good at frequencies higher than 2 Hz. Two-dimensional and three-dimensional (3-D) modeling approaches were applied to the data. As a result of 3-D modeling, we obtained the following features in the resistivity model. The surface layer showed a high resistivity from several hundreds to thousands of ohm-meters and corresponded to the lava. This surface layer covered a highly conductive layer with a resistivity of less than tens of ohm-meters, interpreted as containing seawater or groundwater. However, the basement structure was not clearly detected, except for in an area of northern Sakurajima. The first lava layer was distributed thickly in northern and western parts of Sakurajima, and the boundary between the first and second layers was typically located at around sea level. The conductive second layer was found at deeper levels beneath areas such as the Haruta-yama lava dome and the Nabe-yama pumice cone. This depression of the low resistivity layer is probably caused by the fracture zone associated with previous eruptions, which is formed above the conductive layer. In the proximity of Hikino-hira lava dome and the Taisho crater, the second conductive layer was found at a depth shallower than sea level, suggesting that a hydrothermal system has developed underneath this area. In contrast, elevation of the second layer was not seen on the side of Taisho crater located nearest to the edge of Nabe-yama, implying that a heat source is not present beneath the eastern foot of Sakurajima.
  • Akihiko Terada, Takeshi Hashimoto, Tsuneomi Kagiyama
    BULLETIN OF VOLCANOLOGY 74 (3) 641 - 655 0258-8900 2012/04 [Refereed][Not invited]
     
    The first crater of Nakadake, peak of Aso volcano, Japan, contains a hot water lake that shows interesting variations in water level and temperature. These variations were discovered by precise, continuous observations of the lake independent of precipitation. We developed a numerical model of a hot crater lake and compared with observational data for the period from July 2006 to January 2009. The numerical model revealed seasonal changes in mass flux (75-132 kg/s) and enthalpy (1,840-3,030 kJ/kg) for the fluid supplied to the lake. The relation between the enthalpy and mass flux indicates that the bottom input fluid is a mixture of high- and low-temperature fluids. Assuming a mixture of high-temperature steam at 800A degrees C and liquid water at 100A degrees C, we evaluated the liquid and steam fluxes. The liquid water flux shows a seasonal increase lagging behind the rainy season by 2 months, suggesting that the liquid water is predominantly groundwater. The fluctuation pattern in the flux of the high-temperature steam shows a relation with the amplitude of volcanic tremor, suggesting that heating of the hydrothermal system drives the tremor. Consequently, precise observations of a hot crater lake represent a potential method of monitoring volcanic hydrothermal systems in the shallow parts of the volcanoes.
  • Hashimoto, T, T. Mogi, M. Nishimura, S. Arita, J. Shimizu, T. I, Y. Minamoto, S. Nagamachi
    Geophysical Bulletin of Hokkaido University 北海道大学大学院理学研究院自然史科学部門（地球物理学） 75 (75) 117 - 132 0439-3503 2012/03 [Not refereed][Not invited]
     
    Localized geomagnetic secular changes have been reported in the eastern Hokkaido, previouslyby repeat surveys, and more recently, by continuous recording. Some previous studies discussthe piezo-magnetic field due to stress accumulation by plate subduction. To elucidate the natureof such "anomalous" secular changes in the total field, we started geomagnetic three-componentabsolute measurements. Firstly, we estimated the so-called orientation effect which may becontained in the simple differential total field, by using the results of the absolute measurements.At some stations this effect has been found to be non-negligible. While correcting the orientation effect, we assessed an effect of global-scale secular changesby using the IGRF-11 model. This effect contributes much to regional-scale secular changes inthe eastern Hokkaido. As a result, considerable part of the observed differential total field canbe explained by this component. Then, residuals which deviated from the global secular fieldare obtained, which showed relatively good agreement with the predicted piezo-magnetic field. However, it is still uncertain that the residual field is significant or not, as well as its origin. Our analysis has also revealed an "anomalous" decreasing trend in the total field in the late90s at NIB station which is located at the eastern side of Kussharo caldera. We speculate thatthis anomalous magnetic change may have some relation to the elevated signature of volcanicunrest at Atosanupuri where seismic swarm was followed by significant ground deformation in themid 90s.
  • Hashimoto, T, T. Koyama, T. Kaneko, T. Ohminato, M. Yoshimoto, E. Suzuki, T. Yanagisawa
    Geophysical Bulletin of Hokkaido University 75 145 - 159 0439-3503 2012/03 [Not refereed][Not invited]
  • Takeshi Hashimoto, Takao Koyama, Takayuki Kaneko, Takao Ohminato, Mitsuhiro Yoshimoto, Eiichi Suzuki, Takatoshi Yanagisawa
    Journal of the Hokkaido University, Faculty of Science, Series VII: Geophysics (75) 145 - 159 0441-067X 2012 [Refereed]
     
    The first low-altitude airborne magnetic survey was performed over the summit area of Tarumae Volcano, southwestern Hokkaido, Japan. An unmanned autonomous helicopter was used as the platform for the magnetic survey. Obtained total field anomaly is inverted into a matrix of magnetized prisms, each of which has a uniform magnetization parallel to the present geomagnetic field. Magnetization in the summit atrio ranges from 3 to 8 A/m with an average of 5.3 A/m. The summit lava dome and its vicinity show relatively high magnetization, while the eastern to southwestern part of the atrio is less magnetized. Such variability may be attributed to the difference in magnetization between blocky lava and pyroclastic deposits, as well as to chemical demagnetization due to persistent fumarolic activity at several vents. From the viewpoint of an aeromagnetic survey, high positioning repeatability is one of the most advantageous features of such an unmanned autonomous helicopter. Optimized operation of the system would enable us to detect temporal changes associated with volcanic activity in the future.
  • Hashimoto, T, A. Terada, M. Ejiri, T. Nakamura, M. Abo
    Bull. Volcanol. Soc. Japan 57 (4) 219 - 225 0453-4360 2012 [Refereed][Not invited]
  • Kenji Okazaki, Toru Mogi, Mitsuru Utsugi, Yoshihiko Ito, Hideki Kunishima, Takashi Yamazaki, Yukitsugu Takahashi, Takeshi Hashimoto, Yusuke Ymamaya, Hisatoshi Ito, Hideshi Kaieda, Kazuhiro Tsukuda, Youichi Yuuki, Akira Jomori
    PHYSICS AND CHEMISTRY OF THE EARTH 36 (16) 1237 - 1246 1474-7065 2011 [Refereed][Not invited]
     
    Airborne geophysical surveys enable us to clarify three-dimensional subsurface structures in large and inaccessible areas. Therefore, they have been used recently to investigate large-scale landslides and volcanoes, as well as in mineral and hydrocarbon explorations. This paper describes a geological assessment for tunnel design and construction using helicopter-borne geophysical surveys. Airborne electromagnetic surveys using a grounded electric dipole source and magnetic surveys were conducted to delineate resistivity and magnetization structures in deeper parts of tunnel construction sites in the Otoineppu area of Hokkaido, northern Japan. The survey area is mainly composed of Cretaceous sedimentary rocks, with serpentinite dykes intruded into the sedimentary rocks. The surveys covered the tunnel site and its surroundings to estimate the distribution of sediment rocks and serpentinite. The resistivity structure of deep sections and the distribution of magnetization anomalies delineated the serpentinite types and their distribution, which is useful in understanding potential geotechnical issues when excavating a tunnel. (C) 2011 Elsevier Ltd. All rights reserved.
  • Temporal magnetic changes possibly due to cooling magmas as revealed by repeat helicopter-borne magnetic surveys over an active volcano
    Hashimoto, T, M. Utsugi, T. Nakatsuka, S. Okuma, T. Koyama, W. Kanda
    Proceedings of the 10th SEGJ International Symposium, Kyoto 276 - 279 2011 [Refereed][Not invited]
  • Yamaya Yusuke, Sasai Yoichi, Takeuchi Akihiro, Mogi Toru, Alanis Paul, Cordon Jr Juan, Hashimoto Takeshi, Nagao Toshiyasu
    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN 特定非営利活動法人 日本火山学会 2011 90 - 90 2011
  • Koyama Takao, Kaneko Takayuki, Ohminato Takao, Watanabe Atsushi, Takeo Minoru, Yanagisawa Takatoshi, Hashimoto Takeshi, Honda Yoshiaki
    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN 特定非営利活動法人 日本火山学会 2011 22 - 22 2011
  • Electromagnetic monitoring of Taal volcano: SATREPS-Project 2010-2014
    Nagao, T, A. Takeuchi, Y. Sasai, Y. Yamaya, T. Hashimoto, T. Mogi, Y. Tanaka, P.K. Alanis, J.M. Cordon Jr, J. Sabit, J.S. Sincioco
    Conductivity Anomaly Research 2011 20 - 20 2011 [Not refereed][Not invited]
  • Nakatsuka, T, S. Okuma, Joint Group for, Usu Volcano Airborne Magnetic Survey
    Conductivity Anomaly Research CA研究グループ 2011 37 - 43 2011 [Not refereed][Not invited]
  • Wataru Kanda, Mitsuru Utsugi, Yoshikazu Tanaka, Takeshi Hashimoto, Ikuko Fujii, Toshiaki Hasenaka, Nobuaki Shigeno
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 189 (1-2) 158 - 171 0377-0273 2010/01 [Refereed][Not invited]
     
    Since August 2000, we have recorded the total intensity of the geomagnetic field at the summit area of Kuchi-erabu-jima volcano, where phreatic eruptions have repeatedly occurred. A time series analysis has shown that the variations in the geomagnetic field since 2001 have a strong relationship to an increase in volcanic activity. These variations indicate thermal demagnetization of the subsurface around the presently active crater. The demagnetization source for the early variations, until summer 2002, was estimated at about 200 m below sea level. For the variations since 2003, the source was modeled on the basis of the expansion of a uniformly magnetized ellipsoid. The modeling result showed that the source is located at 300 m above sea level beneath the crater. We carried out an audio-frequency magnetotelluric survey with the aim of obtaining a relation between the demagnetization source and the shallow structure of the volcano. A two-dimensional inversion applied to the data detected two good conductors, a shallow thin one which is restricted to a region around the summit area, while the other extends over the edifice at depths between 200 and 800 m. These conductors are regarded as clay-rich layers with low permeability, which were assumed to be generated through hydrothermal alteration. The demagnetization source for the early variations was possibly located at the lower part of the deep conductor and the source after 2003 lies between the two conductors, where groundwater is considered to be abundant. Based on these results, as well as on seismological, geodetic, and geochemical information, we propose a heating process of the Kuchi-erabu-jima volcano. In the initial stage, high-temperature volcanic gases supplied from the deep-seated magma remained temporarily at the level around the lower part of the less permeable deep conductor since the ascent path had not yet been established. Then, when the pathway developed as a result of repeated earthquakes, it became possible for a massive flux of volcanic gases to ascend through the conductor. The high temperature gases reached the aquifer located above the conductor and the heat was efficiently transported to the surrounding rocks through the groundwater. As a consequence, an abrupt increase of the gas flux and diffusion of the heat through the aquifer occurred and the high-temperature zone expanded. Since the high-temperature zone is located beneath another conductor, which acts as caprock, we assume that the energy of the phreatic explosion is accumulated there. (C) 2009 Elsevier B.V. All rights reserved.
  • Yusuke Yamaya, Toru Mogi, Takeshi Hashimoto, Hiroshi Ichihara
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 187 (3-4) 193 - 202 0377-0273 2009/11 [Refereed][Not invited]
     
    Audio-magnetotelluric (AMT) measurements were recorded in the crater area of Tarumai volcano, northeastern Japan. This survey brought the specific structures beneath the lava dome of Tarumai volcano, enabling us to interpret the relationship between the subsurface structure and fumarolic activity in the vicinity of a lava dome. Three-dimensional resistivity modeling was performed to achieve this purpose. The measured induction vectors pointed toward the center of the dome, implying the topographic effect. However, estimation of the topographic effect showed that the measured vector was not explained only by this effect. This suggested that the distribution of induction vectors still held information of the subsurface structure and could be helpful in determining the geometry of 3-D bodies. The 3-D modeling was based on a quasi-one-dimensional layered structure that included topography. The final model revealed that the andesitic lava dome is characterized by comparatively low resistivity (50 Omega m), and that two conductive bodies (50 and 1-5 Omega m) are present beneath the lava dome. The shallower of these conductors is interpreted as an aquifer, such as a buried crater lake. The deeper, extremely conductive body corresponded to a convecting zone containing rising hydrothermal fluid. The shallower aquifer critically controls the temperature and chemical components of the fumarolic gasses. High-temperature gas supplied from deeper part that encounters the shallow aquifer loses its water-soluble components and heat, resulting in weak and low-temperature fumaroles. In contrast, most of the gas, which ascends outside the area of the shallower aquifer, is released as high-temperature fumaroles. This study provides an insight that the shallow aquifer in the crater area plays a significant role in the property of fumaroles at the volcanic surface. (c) 2009 Elsevier B.V. All rights reserved.
  • Tadashi Nakatsuka, Mitsuru Utsugi, Shigeo Okuma, Yoshikazu Tanaka, Takeshi Hashimoto
    TECTONOPHYSICS 478 (1-2) 3 - 18 0040-1951 2009/11 [Refereed][Not invited]
     
    Repeat aeromagnetic surveys may assist in mapping and monitoring long-term changes associated with volcanic activity. However, when dealing with repeat aeromagnetic survey data, the problem of how to extract the real change of magnetic anomalies from a limited set of observations arises, i.e. the problem of spatial aliasing. Recent development of the generalized mis-tie control method for aeromagnetic surveys flown at variable elevations enables Lis to statistically extract the errors from ambiguous noise Sources. This technique call be applied to overcome the spatial alias effect when detecting magnetic anomaly changes between aeromagnetic surveys flown at different times. We Successfully apply this technique to Asama Volcano, one of the active volcanoes in Japan, which erupted in 2004. Following the volcanic activity in 2005, we conducted a helicopter-borne aeromagnetic survey, which we compare here to the result from a previous survey flown in 1992. To discuss small changes in magnetic anomalies induced by volcanic activity, it is essential to estimate the accuracy of the reference and the repeat aeromagnetic measurements and the probable errors induced by data processing. In our Case. the positioning inaccuracy of the 1992 reference survey was the most serious factor affecting the estimation of the magnetic anomaly change because GPS was still in all early stage at that time. However, Our analysis revealed that the magnetic anomaly change over the Asama Volcano area from 1992 to 2005 exceeded the estimated error at three locations, one of which is interpreted as a loss of magnetization induced by volcanic activity. In this study, we suffered from the problem of positioning inaccuracy ill the 1992 survey data, and it was important to evaluate its effect when deriving the magnetic anomaly change. (C) 2009 Elsevier B.V. All rights reserved.
  • Hiroshi Aoyama, Shin'ya Onizawa, Tomokadu Kobayashi, Takeshi Tameguri, Takeshi Hashimoto, Hiromitsu Oshima, Hitoshi Y. Mori
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 187 (3-4) 203 - 217 0377-0273 2009/11 [Refereed][Not invited]
     
    Post-eruptive crustal activity after the 2000 eruption of Usu volcano was investigated by seismic and geodetic field observations. Remarkable features of the magmatic eruptions that occur almost every 30 years include lava dome formation and strong precursory earthquakes. On the other hand, rapid dome subsidence was observed by electronic distance meter (EDM) measurement after the 1977-1982 summit eruption. Since the 2000 eruption, seismic activity at a shallow part under the summit crater has remained at a high level relative to that after the 1977-1982 eruption, although eruption occurred at the western foot of the volcano during the 2000 eruption. To reveal the shallow crustal activity in the inter-eruptive period around the summit area, seismicity and crustal deformation have been investigated since 2006. Dense temporary seismic observations and hypocenter relocation analysis using a three-dimensional velocity structure model revealed that the focal area is localized along the U-shaped fault that developed in the dome-forming stage of the 1977-1982 eruption. Three major focal clusters are distributed on the southwestern side of Usu-Shinzan cryptodome, which was built up during the 1977-1982 eruption. For the seven major events with magnitudes larger than 1, the focal mechanism was a large dip-slip component, which suggests the subsidence of Usu-Shinzan cryptodome. Interferomatetric satellite aperture radar (InSAR) image analysis and repeated GPS measurements revealed subsidence of the summit dome, which is almost centered at the Usu-Shinzan cryptodome. The area of rapid deformation is restricted to a small area around the summit crater. The estimated rate of dome subsidence relative to the crater floor is about 3 cm/year. These results strongly suggest that subsidence of Usu-Shinzan is associated with the small earthquakes along the U-shaped fault that surrounds the cryptodome. According to prior seismic and geodetic studies, it is thought that most of the magma rising under the summit crater during the 2000 eruption stopped around a depth of 2 km below sea level, which is sufficiently deep relative to the focal area of the present seismicity. A part of the magma intruded under the western foot and contributed to the 2000 eruption. We conclude that the 2000 eruption scarcely affected the shallow crustal activity under the summit crater, and that Usu-Shinzan cryptodome is continuing to subside just as it was before the 2000 eruption. The shallow volcanic earthquakes that began increasing from 1995 are closely related to the successive subsidence of the summit domes. Temporal change in fumarole temperature suggests a relationship between the shallow earthquakes and cooling of the magma that intruded under Usu-Shinzan during the 1977-1982 eruption. (c) 2009 Elsevier B.V. All rights reserved.
  • Hideaki Hase, Takeshi Hashimoto, Yasunori Nishida, Mtsuru Ursugi, Hiroyuki Inoue, Mzue Saba
    Journal of the Geothermal Research Society of Japan 31 (1) 27 - 37 1883-5775 2009 [Refereed][Not invited]
     
    Usu volcano is located at southwestern part of Hokkaido, which is one of the most active volcanoes in Japan. We conducted self-potential (SP) surveys on the volcano, since July to December 2006. The compiled SP map reveals positive anomalies around Gin-numa crater and northwestern part of Ko-Usu, and a negative anomaly on the top of O-Usu lava dome on the summit caldera. The locations of the positive anomalies are corresponding to the fumarolric area, which are likely to be affected by hydrothermal system beneath the volcano. To confirm the consideration, we conducted numerical simulations of groundwater flow and SP of the electrokinetic origin within the volcano. The simulation results indicated the existences of, (a) hydrothermal upwelling driven by the intruded conduit beneath Usu-shinzan as a heat source, (b) a caprock layer at the upper margin of the hydrothermal and (c) low-resistivity channels from the upper margin of the hydrothermal area to the surface. © 2009, THE GEOTHERMAL RESEARCH SOCIETY OF JAPAN. All rights reserved.
  • Wataru Kanda, Yoshikazu Tanaka, Mitsuru Utsugi, Shinichi Takakura, Takeshi Hashimoto, Hiroyuki Inoue
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 178 (1) 32 - 45 0377-0273 2008/11 [Refereed][Not invited]
     
    The 1st crater of Naka-dake, Aso volcano, is one of the most active craters in Japan, and known to have a characteristic cycle of activity that consists of the formation of a crater lake, drying-tip of the lake water, and finally a Strombolian-type eruption. Recent observations indicate an increase in eruptive activity including a decrease in the level of the lake water, mud eruptions, and red hot glows on the crater wall. Temporal variations in the geomagnetic field observed around the craters of Naka-dake also indicate that thermal demagnetization of the subsurface rocks has been occurring in shallow subsurface areas around the 1st crater. Volcanic explosions act to release the energy transferred from magma or volcanic fluids. Measurement of the subsurface electrical resistivity is a promising method in investigating the shallow structure of the volcanic edifices, where energy from various sources accumulates, and in investigating the behaviors of magma and volcanic fluids. We carried out audio-frequency magnetotelluric surveys around the craters of Naka-dake in 2004 and 2005 to determine the detailed electrical structure down to a depth of around 1 km. The main objective of this study is to identify the specific subsurface structure that acts to store energy as a preparation zone for volcanic eruption. Two-dimensional inversions were applied to four profiles across the craters, revealing a strongly conductive zone at several hundred meters depth beneath the 1st crater and surrounding area. In contrast, we found no such remarkable conductor at shallow depths beneath the 4th crater, which has been inactive for 70 years, finding instead a relatively resistive body. The distribution of the rotational invariant of the magnetotelluric impedance tensor is consistent with the inversion results. This unusual shallow structure probably reflects the existence of a supply path of high-temperature volcanic gases to the crater bottom. We propose that the tipper part of the conductor identified beneath the 1st crater is mainly composed of hydrothermally altered zone that acts both as a cap to upwelling fluids supplied from deep-level magma and as a floor to infiltrating fluid from the crater lake. The relatively resistive body found beneath the 4th crater represents consolidated magma. These results suggest that the shallow conductor beneath the active crater is closely related to a component of the mechanism that controls volcanic activity within Naka-dake. (C) 2008 Elsevier B.V. All rights reserved.
  • T. Hashimoto, T. Hurst, A. Suzuki, T. Mogi, Y. Yamaya, M. Tamura
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 176 (4) 610 - 616 0377-0273 2008/10 [Refereed][Not invited]
     
    Volcanic eruptions can produce large magnetic field changes by thermomagnetic effects, especially when magma cools from high temperatures and acquires a permanent magnetisation from the Earth's magnetic field. After the 2000 eruption Of Mt Usu, Japan, significant magnetic field changes were observed not only in the vicinity of the magmatic intrusion but also in an area some distance away that Was unlikely to be at a temperature near the Curie Point. The magnetic changes in the latter area appear to be caused by thermal viscous remanent magnetisation (TVRM), in which the elevated subsurface temperatures have accelerated the acquisition of magnetisation parallel to the existing Earth's field in the ground material. The unusually large changes (up to 40 nT/yr) are probably because of underlying reversely magnetised Pleistocene rocks, which are being normally remagnetised by exposure to temperatures of over 200 degrees C. We made an order of magnitude estimate of the likely effects of TVRM in this case, based on some previous laboratory studies, which confirms that TVRM is a plausible mechanism for the observed magnetic changes. This paper provides probably the first held example in which a natural TVRM process associated with ongoing volcanic activity has been observed. This indicates that even when temperatures are well below the Curie Point, significant magnetic changes can Occur on active volcanoes. In many cases, areas of recent volcanism are dominated by normal magnetisation and thus the TVRM only plays a minor role in volcanomagnetic changes. It will, however, be a significant effect when materials with reversed or randomly-oriented magnetisation are moderately reheated through volcanic activity. We emphasize that separation of thermal viscous magnetisation from thermal magnetisation will sometimes be necessary for properly interpreting magnetic changes around volcanoes, especially in relation to ongoing volcanic activities. (C) 2008 Elsevier B.V. All rights reserved.
  • Wahyu Srigutomo, Tsuneomi Kagiyama, Wataru Kanda, Hiroshi Munekane, Takeshi Hashimoto, Yoshikazu Tanaka, Hisashi Utada, Mitsuru Utsugi
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 175 (1-2) 231 - 240 0377-0273 2008/07 [Refereed][Not invited]
     
    Time-domain electromagnetic (TDEM) surveys were carried out around Unzen Volcano, Shimabara Peninsula, South-west Japan in 2001 and 2002 in the eastern part of the peninsula. The surveys were a completion of the previously interpreted TDEM data collected from surveys in 1995 in the western part of the peninsula. Interpretation of the recorded transient magnetic fields resulted in a general feature of the resistivity structure which are composed of three main layers: a resistive surface layer, a conductive layer (below 10 Omega m) from about sea level to 2.5 km below the surface, and a third resistive layer. The conductive layer is considered to be a complex of water-saturated and altered layers which spreads widely beneath Shimabara Peninsula. The spatial conductance distribution shows a W-E trending pattern of high conductance from Tachibana Bay to the summit of Unzen (Fugen-Dake). This evidence indicates that volcanic gas was supplied to shallow layer in the western part of the peninsula, which is in accordance with the path of magma migration derived from seismic and deformation studies. Another high conductance zone was also found near Mayu-Yama in the eastern part of Shimabara Peninsula, indicating magma degassing process due to the possibility of the presence of a magma system beneath it. (C) 2008 Elsevier B.V. All rights reserved.
  • Koki Aizawa, Yasuo Ogawa, Takeshi Hashimoto, Takao Koyama, Wataru Kanda, Yusuke Yamaya, Masaaki Mishina, Tsuneomi Kagiyama
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 173 (3-4) 165 - 177 0377-0273 2008/06 [Refereed][Not invited]
     
    Asama volcano is an active volcano with many historical records of Vulcanian eruptions. Its most recent eruptions occurred in 2004 at the summit crater. In this paper, we argue the resistivity structure shallower than 3 km obtained by a dense magnetotelluric survey. The magnetotelluric data were obtained at 74 measurement sites mainly along the four survey lines across the volcano. The resistivity profiles obtained by two-dimensional inversions are characterized by a resistive surface layer and an underlying conductive layer. The dominant feature of the profiles is the existence of resistive bodies at a depth range of a few hundred meters to a few kilometers surrounded by a highly conductive region. Considering that the location of resistive bodies correspond to the old eruption centers (one corresponds to the 24 ka collapse caldera and the other to the 21 ka lava dome), the resistive bodies imply zones of old and solidified intrusive magma with low porosity. Because geothermal activities exist near the resistive bodies, the enclosing highly conductive regions are interpreted as a hydrothermal system driven by the heat from the old solidified magma. Beneath the resistive body under the collapsed caldera, intrusion of magma is inferred from the studies of volcano-tectonic earthquakes and continuous global positioning system (GPS) observation, implying the structural control of magma activity within the volcano. In this study, we propose that the magma ascent was impeded by the old and solidified remnant magma and partly migrated horizontally to the east and finally ascended to the summit, resulting in the 2004 eruptions. (C) 2008 Elsevier B.V. All rights reserved.
  • 佐波 瑞恵, 茂木 透, 西田 泰典, 橋本 武志, 田村 慎
    Geophysical bulletin of Hokkaido University 北海道大学大学院理学研究院自然史科学部門（地球物理学） (71) 49 - 59 0439-3503 2008/03 
    Cooling of intruded magma, development and decay of hydrothermal systems are investigated by model calculations for various combination of parameters such as hydraulic permeability of the intruded magma and its surroundings. Dependence of the pressure gradient on the hydrothermal systems is also investigated to inspect the effect of the potential flow of the groundwater along the topography. In the case that the horizontal pressure gradient is smaller than buoyancy, the hydrothermal system develops just above the intruded magma, while the greater pressure gradient as well as high permeability of surroundings carries the hydrothermal system to downstream. We applied these examinations to the newly formed Nishiyama geothermal field at the time of the 2000 Usu eruption. Numerical calculations considering the real topography in and around the Nishiyama geothermal field well reproduce the observed temporal variations of geothermal field appeared on the ground surface, assuming the in-situ hydraulic permeability of the intruded magma and the surroundings as l0－12～10－13m2 and 10－l0～10－11m2, respectively.
  • Takeshi Saito, Shinji Ohsawa, Takeshi Hashimoto, Akihiko Terada, Shinyo Shikawa, Takahiro Ohkuea
    Journal of the Geothermal Research Society of Japan 30 (2) 107 - 120 1883-5775 2008 [Refereed][Not invited]
     
    Morphometric observations of the crater lake at Aso Volcano, Japan, was carried out and the change of its water level, surface area and water volume between Aug 2000 and Aug 2003 were estimated. The lake water was sampled three times during this period and the concentrations of chloride in the water were measured. Mass balance was evaluated by solving the water and chloride budgets simultaneously. Results showed that the lake water was mainly supplied by volcanic input (3500-6200 ton/day) which occupied at least 60% of the water influx. Meteoric water flux (420-2500 ton/day) was not dominant, which occupied less than 20% of the water influx between Aug 2000 and Apr 2003. Lake water was mainly dissipated by evaporation from the lake surface (3800-5900 ton/day). Seepage from the lake bottom (880-2200 ton/day) occupied about 13-37% of the water outfiux. Heat balance indicated that thermal energy of volcanic input was about 150-200 MW, which occupied more than 95% of energy influx. Most heat loss occurred at the lake surface through evaporation (100-150 MW). The specific enthalpy of volcanic input was estimated to be about 2500-4200 kJ/kg, which corresponds to the enthalpy of superheated steam at several hundred degrees C. It was suggested that mass and heat are input into the lake by the addition of superheated steam at several hundred degrees C. Water flux and enthalpy of volcanic input between Apr 2003 and Aug 2003 were estimated to be larger than those between Aug 2000 and Apr 2003. This is consistent with the observation that the water temperature became higher, the water level was decreased and small mud eruption was occurred. Our results indicate that the crater lake at Aso ranks among the peak-activity volcanic lakes in the world. © 2008, THE GEOTHERMAL RESEARCH SOCIETY OF JAPAN. All rights reserved.
  • Akihiko Terada, Takeshi Hashimoto, Tsuneomi Kagiyama, Hisashi Sasaki
    EARTH PLANETS AND SPACE 60 (6) 705 - 710 1343-8832 2008 [Refereed][Not invited]
     
    A high-resolution Digital Surface Model and a commercial digital camera have enabled precise and continuous monitoring of the crater lake at Aso volcano. From July 2006 onwards, infrared (IR) thermometry has been used with this system, enabling more accurate measurements of lake volume and temperature based on simple and intensive observations than has been possible in any other previous studies. The heat discharge remained largely constant at approximately 220 MW, with the exception of an abrupt increase to 280 MW that coincided with a rapid decrease in the water level in August 2007. Simultaneously, an increase in temperature at a shallow depth was suggested by other observations. The crater take was found to respond to even slight changes in volcanic fluid supply, which can be well quantified by our method. Thus, a crater lake can be monitored more precisely than subaerial fumaroles whose energy estimation is often accompanied by large uncertainties. Our monitoring technique of a crater lake provides information on the subsurface hydrothermal system beneath it, for which any in-situ measurements are practically impossible.
  • Hideki Murakami, Naoto Oshiman, Satoru Yamaguchi, Takeshi Hashimoto, Ryokei Yoshimura
    TECTONOPHYSICS 443 (3-4) 200 - 208 0040-1951 2007/10 [Refereed][Not invited]
     
    The Nojima Fault Zone Probe was designed to study the properties and healing processes of the Nojima fault, which is the surface fault rupture of the Hyogo-ken Nanbu earthquake (M7.2) of 1995 (1995 Kobe earthquake). In this project, water injection experiments were conducted in a borehole of 1800 m depth at the Nojima fault. We set up electrodes around the borehole and observed self-potential variations to investigate the magnitude of electrokinetic and hydraulic parameters around the Nojima fault zone. In the 1997 experiment, self-potential variations were in the range of a few to about 20 mV across 320-450 m electrode dipoles with hydraulic pressure variations from 3.5 to 4 NlPa. In the 2000 experiment, self-potential variations were in the range of a few to about 85 mV across 160-260 m electrode dipoles with the hydraulic pressure variations from 3 to 4.5 MPa. In the 2003 experiment, self-potential variations were in the range of a few to about 30 mV across 20-80 m electrode dipoles with hydraulic pressure of 4 MPa. These observed self-potential variations were explained well with an electrokinetic effect due to the underground flow of the injected water. From the observed results, we estimated that the ratio of hydraulic parameters (permeability, porosity, and tortuosity) to electrokinetic parameters (zeta potential and dielectric constant) decreased approximately 40% during eight years after the earthquake. This result suggests that the healing process around the fault zone progress. (C) 2007 Elsevier B.V. All rights reserved.
  • 岡崎紀俊, 大津直, 廣瀬亘, 石丸聡, 田村慎, 川上源太郎, 田近淳, 高橋浩晃, 橋本武志, 茂木透, 笠原稔
    北海道立地質研究所調査研究報告(CD-ROM) (35) 150P,SUPPL 1P  2007/03/30 [Not refereed][Not invited]
  • Yoichi Sasai, Malcom J. S. Johnston, Yoshikazu Tanaka, Robert Mueller, Takeshi Hashimoto, Mitsuru Utsugi, Shinya Sakanaka, Makoto Uyeshima, Jacques Zlotnicki, Paul Yvetot
    ANNALS OF GEOPHYSICS 50 (1) 93 - 104 1593-5213 2007/02 [Refereed][Not invited]
     
    We show that using borehole measurements in tectonomagnetic experiments allows enhancement of the observed signals. New magnetic dipoles, which vary with stress changes from mechanical sources, are produced on the walls of the borehole. We evaluate such an effect quantitatively. First we formulate a general expression for the borehole effect due to any arbitrary source models. This is valid everywhere above the ground surface as well as within the cylindrical hole. A first-order approximate solution is given by a line of horizontal dipoles and vertical quadrupoles along the central axis of the borehole, which is valid above the ground surface and a slightly away (several tens of cm) from the top of the borehole. Selecting the Mogi model as an example, we numerically evaluated the borehole effect. It turned out that the vertical quadrupoles produce two orders of magnitude more intense magnetic field than the horizontal dipoles. The borehole effect is very local, i.e. detectable only within a few in from its outlet, since it is of the same order or more than the case without a borehole. However, magnetic lines of force cannot reach the ground surface from a deeper portion (>10 m) of a borehole.
  • Micro-earthquake activity at Usu volcano revealed by temporary dense observation
    Hiroshi Aoyama, Shin'ya Onizawa, Takeshi Tameguri, Atsuo Suzuki, Tokumitsu Maekawa, Hiromitsu Oshima, Hitoshi Mori, Takeshi Hashimoto, Toru Shiga, Hiroshi Koyama, Masaki Nakahashi, Akifumi Yoshikawa, Yoshirou Fukuyama
    Journal of the Hokkaido University, Faculty of Science, Series VII: Geophysics (70) 107 - 121 0441-067X 2007 
    We performed temporary dense observation at Usu volcano in summer 2006, aiming to reveal micro-earthquake activity under the summit crater during dormant period of the volcanic activity. During about 80 days of temporary observation, more than 330 volcanic earthquakes were observed. Of these earthquakes, well-recorded 142 events are selected for relocation analysis assuming the 3D-velocity structure model which is a result of the explosion seismic experiment at Usu volcano in 2001. Following the result of relocation, we estimated focal mechanism of 7 earthquakes whose magnitudes are more than 1.0. The temporal observation and analyses gave us three new insights about seismic activity 1) Continuous activity of volcanic earthquake is seen at the shallow part under the southern crater floor, 2) Hypocentral regions are distributed along the SW end of the U-shaped fault which was built in the 1977-1982 eruption associated with the uplift of Usu-Shinzan crypt dome, 3) Strike direction of the 7 major earthquakes are almost parallel to the U-shaped fault, and dominant mechanism is dip-slip type which suggests subsidence of summit domes relative to the southern crater floor.
  • Geomagnetic changes due to doming - The 2000 eruption of Usu volcano
    Takeshi Hashimoto, Tohru Mogi, Yasunori Nishida, Masamitsu Takada, Atsuo Suzuki, Tokumitsu Maekawa, Hideyuki Satoh
    Journal of the Hokkaido University, Faculty of Science, Series VII: Geophysics (70) 123 - 135 0441-067X 2007 
    We investigated geomagnetic changes due to dome-like deformation by using a truncated circular cone model. In the case of the normal magnetization, magnetic total field decreases in the northern side of the uplift center, while it increases in the southern side. We found that the original topography prior to the mound formation does not affect the pattern of this magnetic change. We then apply this calculation to the mound-forming activity in the 2000 eruption of Usu Volcano to infer the magnetic change on the foot of the mound. The expected range of magnetic total field change at the station U01 is -80 to -800 nT which is in the opposite sense to the observed actual change (+70 nT). We examined some alternative mechanisms to compensate this decrease due to the deformation. None of them, however, can be a promising candidate. The most reasonable explanation so far for this contradiction is the reversed magnetization of the Tertiary lava that may comprise the mound.
  • Observation of water vapor with a portable raman lidar -continuous monitoring and field experiments over the forest and at the volcano-
    Nakamura, T, N. Sugimoto, T. Tsuda, M. Abo, T. Hashimoto, A. Terada
    Proceedings of the 23rd International Laser Radar Conference 897 - 900 2006 [Refereed][Not invited]
  • 神田 径, 田中 良和, 宇津木 充, 高倉 伸一, 橋本武志, 井上 寛之, 岡田靖章
    CA研究会2006年論文集 CA研究グループ 86 - 88 2006 [Not refereed][Not invited]
  • 平成17年度浅間山電磁気構造探査の概要
    橋本武志, 茂木 透, 鈴木敦生, 山谷祐介, 三品正明, 中塚 正, 小山悦郎, 小山崇夫, 相澤広記, 平林順一, 松尾元広, 野上建治, 小川康雄, 氏原直人, 鍵山恒臣, 神田 径, 大久保綾子, 田中良和, 宇都智史, 宇津木 充
    CA研究会2006年論文集 79 - 80 2006 [Not refereed][Not invited]
  • Local zero setting of thermoluminescence in milled quartz grains
    A.Takeuchi, H. Nagahama, T. Hashimoto
    11th International Conference on Luminescence and Electron Spin Resonance Dating (Cologne, Germany, July 24-29, 2005), Book of Abstracts 180  2005/07 [Refereed][Invited]
  • K Aizawa, R Yoshimura, N Oshiman, K Yamazaki, T Uto, Y Ogawa, SB Tank, W Kanda, S Sakanaka, Y Furukawa, T Hashimoto, M Uyeshima, T Ogawa, Shiozaki, I, AW Hurst
    EARTH AND PLANETARY SCIENCE LETTERS 235 (1-2) 343 - 355 0012-821X 2005/06 [Refereed][Not invited]
     
    Wideband magnetotelluric (MT) soundings were carried out on Mt. Fuji volcano along a northeast to southwest axis. It was found by two-dimensional inversion using the highest quality data (in the frequency range 1-300 Hz) that a good conductor (resistivity of approximately a few ohm in) was located beneath the Summit with a lateral extent of approximately 4 km. It begins approximately I kin below the ground surface; however, its depth cannot be resolved. In our previous study, an intense positive self-potential (SP) anomaly (approximately 2000 mV), was found around a summit crater having a diameter of approximately 3 kin. We interpreted the presence of the good conductor and positive SP anomaly as a strong indication of an active hydrothermal system. Subsequently, we searched for conduction current sources to explain the SP distribution on the surface by using the resistivity structure determined by the MT inversion. The results obtained were that a positive conduction current source of the order of 1000 A should be located at the top of the conductor. From these results, we deduced that the conductor represents a hydrothermal system in which single-phase (liquid) convection is taking place. Since the resistivity at a distance from the good conductor can be explained by the effect of cold groundwater, the hydrothermal system does not seem to extend throughout the entire body of the volcano, but seems to be confined to the area beneath the summit crater. Finally, an estimate of the order of magnitude of the subsurface hydrothermal flow was performed using a relation between the fluid volume flux and electric current density in the capillary model. The result suggested that there exists fairly low permeability within the shallow part of Mt. Fuji. We speculate that the low permeability in the volcano has a correlation with the confinement of the hydrothermal system and quiescence of volcanic activities, such as low seismicity, no gas emanations, and no natural hot springs. (c) 2005 Elsevier B.V. All rights reserved.
  • H Hase, T Hashimoto, S Sakanaka, W Kanda, Y Tanaka
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 143 (4) 259 - 277 0377-0273 2005/05 [Refereed][Not invited]
     
    We conducted self-potential (SP) surveys sequentially from part to part over the central cones of Aso volcano since August 1998 by December 2001. The compiled SP map revealed large SP anomalies on the central cones. The main feature of the SP map is a `W-shaped' profile along the NS-transect over the central cones. It is probable that this characteristic SP profile is produced by the combination of hydrothermal upwelling in the middle and topographic effect. A positive anomaly showing a large concentric pattern has appeared after correcting the topographic effect. To evaluate this SP anomaly, we implemented a numerical code that calculates electric potential produced by arbitrarily positioned current sources and sinks in any three-dimensional resistivity structure. A layered structure obtained from a time-domain electromagnetic (TDEM) field experiment was used for the resistivity model. The estimated current source is 300 A, being located in a conductive layer around the sea level. Meanwhile, sinks were estimated to sit on a circular area corresponding to the marginal part of the conductive layer. Water and heat budget study gives a lower limit of water mass transfer from depth to the bottom of the crater lake of Nakadake. This value was used to estimate the equivalent current in either case of electro-kinetic (EK) [Mizutani, H., Ishido, T., 1976. A new interpretation of magnetic field variation associated with the Matsushiro earthquakes, J. Geomag. Geoelectr., 28, 179-188.] or rapid fluid disruption (RFD) process [Johnston, M.J.S., Byerlee, J.D., Lockner, D., 2001. Rapid fluid disruption: A source for self-potential anomalies on volcanoes, J. Geophys. Res. 106(133), 4327-4335.]. This comparison suggests that the former process is preferable to explain the observed SP anomaly. From these results we infer a large-scale hydrothermal system beneath the central cones of Aso volcano, in which the fluid flow initiates from the surrounding area, converging to the central vent to transport the heat and materials up to the crater lake of Nakadake through a vapor-filled conduit. (c) 2005 Elsevier B.V. All rights reserved.
  • Wide-band MT survey on Tarumai volcano, Hokkaido -2-D resistivity analysis
    Yusuke Yamaya, Takeshi Hashimoto, Toru Mogi, Atsuo Suzuki, Yasunori Nishida, Kengo Tanimoto, Hitoshi Mori, Akihiko Terada, Masaaki Mishina, Hideaki Hase
    Journal of the Hokkaido University, Faculty of Science, Series VII: Geophysics (68) 127 - 140 0441-067X 2005/03 
    We performed a wide-band MT(Magnetotelluric) survey in and around Tarumai volcano, Hokkaido, Japan. MT survey is useful in clearly defining the resistivity structure related to volcanic regions. The MT data were acquired over a frequency range 5.5 × 10-4Hz - 320 Hz. Applying the remote reference method and manual editing process, we obtained the data from 14 sites. Groom-Beiley's decomposition analysis was applied to the tensor impedance data to estimate the direction of the electromagnetic strike. Subsequently, apparent resistivity and phase data of TM mode were inverted using a two-dimensional MT inversion. The resulting model coincides with geological layers and reveals a conductor near the sea level below the summit. The position of the conductor is in accord with the hypocenters of low frequency earthquakes and with the electric current source of self-potential. Therefore, the conductor may suggest the existence of the crustal fluid mainly occupied by hot water. In near future, a denser MT survey in the crater area of Tarumai volcano is required.
  • 茂木 透, 橋本 武志
    Geophysical bulletin of Hokkaido University 北海道大学大学院理学研究科地球惑星科学専攻（地球物理学） (68) 233 - 241 0439-3503 2005/03
  • Magma supply & emission system of Unzen Volcano deduced from resistivity structure
    Kagiyama, Tsuneomi, Srigutomo, Wahyu, Kanda, Wataru, Hashimoto, Takeshi, Tanaka, Yoshikazu, Ogawa, Tsutomu, Utsugi, Mitsuru
    Extended Abstract of international workshop on Unzen Scientific Drilling Project 2005 41 - 42 2005 [Not refereed][Not invited]
  • AW Hurst, PC Rickerby, BJ Scott, T Hashimoto
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 136 (1-2) 53 - 70 0377-0273 2004/08 [Refereed][Not invited]
     
    For about 15 years after their commencement in 1968, magnetic measurements in the crater of White Island gave a good indication of the state of activity and the likelihood of an eruption episode commencing. During this period, magnetic, thermal, around level and chemical measurements were all generally consistent with a model in which these surface changes were caused by increasing temperatures under the Donald Mound area, in the central sub-crater. In more recent times, there has not been such a relationship between the changes around the remnants of Donald Mound and the volcanic activity, which has become localised in the west sub-crater. It appears that changes under the crater, especially lowering of the ground surface and the water table at the west end of the crater, have meant that eruptions are no longer preceded by heating under Donald Mound. The west sub-crater is not easily accessible for repeat surface surveys. One way in which we might be able to monitor future volcanic activity at White Island would be by repeated aeromagnetic surveys, as the magnetic changes are so large that changes of hundreds of nano Teslas are likely to be observed at practical flying heights. (C) 2004 Elsevier B.V All rights reserved.
  • 宇津木 充, 田中 良和, 橋本 武志
    火山爆発のダイナミックス 95 - 101 2004
  • 宇津木 充, 田中 良和, 橋本 武志
    火山爆発のダイナミックス(平成15年度成果報告書) 95 - 101 2004
  • H Hase, T Ishido, S Takakura, T Hashimoto, K Sato, Y Tanaka
    GEOPHYSICAL RESEARCH LETTERS 30 (23) 0094-8276 2003/12 [Refereed][Not invited]
     
    We deduced the zeta potential of various rocks in Aso caldera from streaming potential measurements in laboratory. In contrast to the conventional observation that the zeta potential of crustal rocks is mostly negative under typical geologic conditions, almost half of the samples equilibrated with dilute KCl solution show positive values of zeta potential at pH 4.5-5.5. The samples showing positive zeta are characterized by relatively low SiO2 content and abundance of elements having high isoelectric points, and found to be localized around the summit of Mt. Takadake where the positive correlation between self-potential (SP) and altitude is observed. We emphasize that measurements of zeta potential of volcanic rocks are very important to give more appropriate interpretations of SP data from volcanic fields.
  • M Nakaboh, H Ono, M Sako, Y Sudo, T Hashimoto, AW Hurst
    GEOPHYSICAL RESEARCH LETTERS 30 (7) 0094-8276 2003/04 [Refereed][Not invited]
     
    [1] A phreatic eruption occurred at Kuju Volcano in October 1995. We deployed an EDM network around the active craters of the volcano just after the eruption. Slope distances of the survey lines in the northern network have tended to contract, whereas those in the southern one extended. The maximum contraction observed in the northern network was 70 cm over 6 years. A spherical volume decrease just beneath a fumarolic area called Iwoyama 700 m north of the new craters is a plausible model for these changes in slope distances. A noteworthy feature is that over 6 years after the phreatic eruption ended, the deflation rate is still approximately linear. We also estimated the thermal energy discharge by fumaroles in the new craters, which proved to be well correlated with the observed deflation rate. It is strongly suggested that deflation of a geothermal reservoir, not any magmatic effect, causes the ground deformation around Iwoyama.
  • HASE HIDEAKI, ISHIDO TSUNEO, HASHIMOTO TAKESHI, KANDA WATARU, SATO KEIKO
    京都大学防災研究所年報 (46B) 787-795 - 795 0386-412X 2003/04 [Not refereed][Not invited]
  • Resistivity structure of Unzen Volcano, Kyushu, Japan from time domain electromagnetic (TDEM) data and its implication to magma-ground water interaction
    Srigutomo, Wahyu, Kagiyama, Tsuneomi, Kanda, Wataru, Hashimoto, Takeshi, Munekane, Hiroshi, Tanaka, Yoshikazu, Utsugi, Mitsuru, Ohminato, Takao
    Abstracts of XXIII General Assembly of IUGG (Week A) 2003 [Not refereed][Not invited]
  • Y Sasai, M Uyeshima, J Zlotnicki, H Utada, T Kagiyama, T Hashimoto, Y Takahashi
    EARTH AND PLANETARY SCIENCE LETTERS 203 (2) 769 - 777 0012-821X 2002/10 [Refereed][Not invited]
     
    Magnetic and electric field variations associated with the 2000 eruption of Miyake-jima volcano are summarized. For about 1 week prior to the July 8 phreatic explosion, significant changes in the total intensity were observed at a few stations, which indicated uprising of a demagnetized area from a depth of 2 km towards the summit: this nonmagnetic source can be regarded as a vacant space itself. Electric and magnetic field variations were observed simultaneously associated with the tilt-step event, which was the abrupt (similar to50 s) inflation at a few km depth within the volcano followed by gradual recovery (similar toseveral hours). The electric field is ascribed to the electrokinetic effect most probably due to forced injection of fluids from the source, while the magnetic field to the piezomagnetic effect due to increased pressure. Large magnetic variations amounting to a few tens of nT were observed at several stations since July 8, and they turned almost flat after the August 18 largest eruption. Magnetic changes are explained mostly by the vanishing of magnetic mass in the summit and additionally by the thermal demagnetization at a rather shallow depth. A large increase in the self-potential by 130 mV was also observed near the summit caldera associated with the August 18 eruption, which suggests that the hydrothermal circulation system sustained within the volcano for the past more than 10 years was destroyed by this eruption. (C) 2002 Published by Elsevier Science B.V.
  • Nakaboh, M, Ono, H, Sako, M, Sudo, Y, Hashimoto, T, Hurst, A. W
    Geophys. Res. Lett. 30 (7) 2002 [Refereed][Not invited]
  • Yamaguchi, S, S. Sutoh, T. Hashimoto, H. Murakami, N. Takagi
    J. Seismol. Soc. Japan 日本地震学会 55 (2) 143 - 151 0037-1114 2002 [Refereed][Not invited]
  • Measurements of zeta potential in various rock samples of Aso Volcano
    Hideaki Hase, Shin’ichi Takakura, Tsuneo Ishido, Keiko Sato, Takeshi Hashimoto, Yoshikazu Tanaka
    Annual Report - Institute for Geothermal Sciences, Graduate School of Science, Kyoto University 2001 (B) 2 - 3 2002 [Not refereed][Not invited]
  • 電磁気観測から推定される雲仙火山におけるマグマと水の相互作用
    鍵山恒臣, 橋本武志, Srigutomo, Wahyu, 神田 径, 田中良和, 宇津木 充
    月刊地球 858 - 865 2002 [Not refereed][Not invited]
  • H Murakami, T Hashimoto, N Oshiman, S Yamaguchi, Y Honkura, N Sumitomo
    ISLAND ARC 10 (3-4) 244 - 251 1038-4871 2001/09 [Refereed][Not invited]
     
    Self-potential variations were measured to estimate the magnitude of electrokinetic and hydrological parameters (zeta potential and permeability) of the Nojima Fault zone in Awaji, Japan. The study observed self-potential variations that seemed to be associated with water flow from the injection well to the fracture zone, which were induced by turning the injection on and off. Amplitudes of the variations were a few to 0.03 V across 320-450 m dipoles. These variations can be explained well with an electrokinetic model. The quantity k/zeta (permeability/zeta potential) is in the range 1.6 x 10(-13) - 5.4 x 10(-13) m(2)/V. Permeability of the Nojima fault zone can be estimated as approximately 10(-16)-10(-15) m(2) on the assumption that the zeta potential is in the range -0.01 to -0.001 V.
  • T Hashimoto
    ISLAND ARC 10 (3-4) 306 - 317 1038-4871 2001/09 [Refereed][Not invited]
     
    A resistivity survey method using artificial telluric noise was examined and applied to a field of a fault zone. The electric earth current was measured at 50 sites in the Nojima Fault zone, which is in the northwestern part of Awaji Island, southwestern Japan. The dominant component of the observed electric field is supposed to be leakage currents from DC electric railways running outside the island. Amplitude and polarization of the stray current were systematically investigated and were revealed to represent the subsurface electrical structure of the study area. Some features on the fault zone's electrical structure have been pointed out, including: (i) an electrical boundary that corresponds to a geological one between granite (resistive) and sediments (conductive); and (ii) a low resistivity spot on the surface rupture of the earthquake fault. The structure estimated in the present study is both qualitatively and quantitatively consistent with previous resistivity surveys done using other methods pursued in the same area. It shows the validity of the 'stray current method' as one that is easy and uses low-cost resistivity exploration tools in a region where the effect of artificial noise caused mainly by leakage currents from electrical railways cannot be ignored.
  • Sasai, Y, M. Uyeshima, H. Utada, T. Kagiyama, J. Zlotnicki, T. Hashimoto, Y. Takahashi
    Journal of Geography 学術雑誌目次速報データベース由来 110 (2) 226 - 244 0022-135X 2001 [Refereed][Not invited]
     
    Electric and magnetic field observations have been extensively carried out since 1995. A precursory magnetic anomaly was detected in July 1996, which was ascribed to thermal demagnetization at a depth of several hundreds of meters beneath the southern periphery of the summit Hatcho-taira caldera. Magnetic data revealed that the large depression at the summit associated with the steam explosion on July 8, 2000 had been completed within four minutes. Since the beginning of July, anomalous magnetic changes were observed at several magnetometer sites along the central N-S line of Miyake-jima volcano, which indicated the rise of a demagnetized area from depth to the summit. On July 4, a few days before the steam explosion, an area survey of SP in the summit caldera was conducted, discovering an extremely negative zone around the forthcoming depression, which suggested the intense absorption of ground water. Tilt-step events; i.e., abrupt uplifts around the summit area, were accompanied by electric field variations, which were very similar to the velocity waveform of the ground motion, as well as magnetic variations with step-like changes. An electric field can be interpreted as being due to electric currents generated by the forced injection of steam and/or water from the pressure source (electrokinetic phenomena). Magnetic changes are attributed to the piezomagnetic effect of rocks due to increased stresses. The geomagnetic total intensity showed large variations after the July 8 eruption, the typical feature of which was positive at the east and west sides and negative along the central north-south line of the volcano. They are ascribed to 1) the loss of magnetic mass from the summit and 2) the thermal demagnetization at depth. After the August 18 eruption, which was the largest, the steep changes in total intensity became flat, which suggested that the temperature rise at depth had weakened. At the time of the August 18 eruption, a large increase in self-potential was observed around the southwestern foot of the central cone Oyama : This implies that a definite change occurred in the hydrothermal system of the volcano.
  • Srigutomo W., Kagiyama T., Kanda W., Hashimoto T., Munekane H., Tanaka Y., Utsugi M., Ominato T.
    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN 特定非営利活動法人 日本火山学会 2001 110 - 110 2001
  • SASAI Yoichi, UYESHIMA Makoto, UTADA Hisashi, KAGIYAMA Tsuneomi, ZLOTNICKI Jacques
    J. Geogr. Tokyo Geographical Society 110 (2) Plate7 - Plate8 0022-135X 2001 [Not refereed][Not invited]
  • Nishida Y., Mogi T., Sato H., Tanimoto K., Saba M., Takada M., Tanaka Y., Hashimoto T., Utsuki M., Sasai Y.
    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN 特定非営利活動法人 日本火山学会 2000 173 - 173 2000
  • ASOBOI 97: Aso Seismic Observation with Broadband Instruments in 1997
    Yamamoto,M, H.Kawakatsu, S.Kaneshima, T.Iidaka, J.Oikawa, S.Watada, Y.Morita, T.Mori, T.Tsutsui, Y.Sudo, S.Yoshikawa, T.Hashimoto, M.Nakaboh
    Bull. Earthq. Res. Inst., Univ. Tokyo 74 267 - 285 1999 [Not refereed][Not invited]
  • Y Sudo, H Ono, AW Hurst, T Tsutsui, T Mori, M Nakaboh, Y Matsumoto, M Sako, S Yoshikawa, M Tanaka, Y Kobayashi, T Hashimoto, T Hoka, T Yamada, H Masuda, S Kikuchi
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 81 (3-4) 245 - 267 0377-0273 1998/05 [Refereed][Not invited]
     
    Kuju Volcano lies near Aso Caldera in central Kyushu. After a few hundred years of dormancy, a phreatic eruption began with the ejection of about 20,000 m(3) ash on 11 October 1995. A number of new vents have opened on a series of lines striking east-west on the eastern slope of Mt. Hossho, one of the domes of the Kuju complex, a few hundred meters from a pre-existing fumarolic area. After the eruption, there has been continuous steam emission from the new vents. There was the second ash eruption in December 1995. Before these eruptions, seismic events were rarely observed, either near the site of the new vents, or elsewhere under Kuju Volcano. In the nearly 2 years since the first eruption, several thousand earthquakes have been recorded. These events have been very horizontally concentrated just to the north of the new vents vertically between 800 m above sea level and 1000 m below sea level. Very few earthquakes have been located on the southern side of the new vents. There was clearly a strong high-frequency attenuation affecting the seismic waves which passed through the region beneath the new vents to the seismometers south of Mt. Hossho. This evidence possibly indicates a thermal fluid content beneath the new vents, suggesting that there is a seismic attenuating zone in the feeding area of the new vents. Nearly all the earthquake spectra were of dominantly high-frequency, but the percentage of earthquakes with predominantly low-frequency spectra increased at times of enhanced volcanic activity. Volcanic tremors were also observed around the times of peak activity. Slope distance measurements have been made since the eruption. The main results of these measurements are a contraction of more than 200 ppm in distances between Mt. Hossho and points further north. The significant distance changes occurred during seismic swarms. This indicated that the seismic activities influenced ground deformation, even though some of these swarms were 3 or 5 lan from Mt. Hossho. The slope distance changes indicate that an area near the top of Mt. Hossho has been moving to the northeast. (C) 1998 Elsevier Science B.V. All rights reserved.
  • N Sumitomo, N Oshiman, S Sakanaka, T Goto, H Utada, Y Sasai, M Uyeshima, S Koyama, R Ishikawa, Y Honkura, H Tsunakawa, S Yamaguchi, H Inokuchi, H Murakami, Shiozaki, I, Y Tanaka, T Hashimoto, T Mogi, T Uchida, A Jomori, K Suzuki
    JOURNAL OF PHYSICS OF THE EARTH 45 (2) 91 - 104 0022-3743 1997 [Refereed][Not invited]
     
    In association with the 1995 Hyogo-ken Nanbu earthquake, we observed changes in the telluric field by about 10 mV/km about 10 s after the origin time with some long-span electrical dipole network located at about 70 km from the epicenter. After the occurrence of the earthquake, electric and magnetic measurements such as DC resistivity, VLF-MT, self-potential, and the geomagnetic total intensity across the Nojima fault were made at several places in Awaji Island, The low resistive zone beneath the western side of the fault was found in the derived resistivity structure of the shallower portion of the fault in Hirabayashi. On the other hand, however, no significant anomaly associated with the fault structure was found from the measurements of total intensity and self-potential. Prior to the occurrence of the main shock, no geomagnetic or electric continuous stations existed near the focal area. Approximately within 1 week after the occurrence of the main shock, we set up 10 continuous observation sites for the geomagnetic total intensity in the focal area in order to detect geomagnetic changes due to stress change caused by the aftershock activity. No changes in the total intensity in association with the individual aftershock activity have been observed so far. However, systematic temporal trends in the geomagnetic differences have been observed, especially at sites in the northern half of the observation area.
  • T Hashimoto
    JOURNAL OF GEOMAGNETISM AND GEOELECTRICITY 49 (7) 977 - 993 0022-1392 1997 [Refereed][Not invited]
     
    The evolution of a hydrothermal system beneath the Unzen Volcano, one of the dacitic volcanoes in Shimabara peninsula, southwest Japan, was investigated by self-potential (SP) observations during the 1990-1995 eruption events. SP changes accompanying the eruption can be divided into three stages. In the first stage, March through June of 1991, the rapid growth of a distinct positive SP anomaly was detected by continuous observation in the vicinity of a lava dome which began extrusion in May 1991. The positive anomaly is thought to be caused by hydrothermal upflows induced around the intruded magma through electrokinetic coupling. In the second stage, July 1991 through December 1993, the lava dome erupted in an exogenous manner. The growth of a dipolar SP anomaly was detected by repeated surveys during this stage. The cause of this SP change is thought to be electrokinetic potentials associated with shallow hydrothermal circulation which grew at the west of the lava dome for over two years. In the third stage, from the beginning of 1994, the dome growth became endogenous. SP showed concentric increase around the dome. This SP change probably suggests the expansion of upflow zone at high temperature in shallow levels.
  • 1994年地殻比抵抗研究グループ合同観測における宮崎―水俣測線のMT比抵抗モデル
    市來雅啓, 大志万直人, 住友則彦, 橋本武志, 槇野豊, 歌田久司, 鍵山恒臣, 宗包浩志, 岩切一宏
    Conductivity Anomaly研究会論文集 1997 [Not refereed][Not invited]
  • T Iyemori, M Takeda, A Saito, T Araki, T Hashimoto, Y Tanaka
    JOURNAL OF GEOMAGNETISM AND GEOELECTRICITY 48 (10) 1219 - 1232 0022-1392 1996 [Refereed][Not invited]
     
    The solar and IMF effects were statistically detected in mid-latitude (L = 1.25) ionospheric electric field data obtained by the MU radar. It was found that the IMF-B-x component (sector polarity) and the solar radio flux (SRF) correlates with the north-south component of the electric field on the night-side. For more positive (sunward) B-x, or for greater SRF, the electric field is more southward/downward. However, strong mutual correlation between the IMF-B-x and the SRF is found in the period analyzed (1987-1993), suggesting that the night-side correlation between electric fields and IMF-B-x comes from the effect of the solar activity rather than the direct influence of the IMF-B-x. In fact it was also found from the data for almost two solar cycles that the IMF-B-x (or B-y) dependence of the ionospheric foF2 is very similar with the solar activity (sunspot number) dependence of it. This suggests that the mutual correlation between the solar activity and the IMF-B-x (or B-y) causes the apparent correlation of the foF2 with the IMF-B-x which has been reported as a sector polarity effect. On the other hand, the direct effects of the IMF-B-x (or B-y) on the electric fields were also detected by taking the correlations between the time differentials of them and the results are consistent with the known IMF effects on the S-q focus location. The differentials of the IMF-B-z have significant correlation with the electric fields in limited local time zones and the sense of electric field is consistent with the penetration of the dawn-to-dusk electric field in the magnetosphere indicating the imperfect shielding by the plasmasphere.
  • T Iyemori, T Kamei, Y Tanaka, M Takeda, T Hashimoto, T Araki, T Okamoto, K Watanabe, N Sumitomo, N Oshiman
    JOURNAL OF GEOMAGNETISM AND GEOELECTRICITY 48 (8) 1059 - 1070 0022-1392 1996 [Refereed][Not invited]
     
    Impulsive co-seismic geomagnetic variations were observed at two stations nearly 100 km apart from the source region of the 1995 Hyogoken-Nanbu earthquake (M = 7.2). The maximum amplitude at the main shock was 0.6 similar to 1.0 nT and the duration was 20 similar to 30 seconds. These variations seem to have commenced at the origin time and before the arrival of the seismic waves to the observation site of 17 seconds later. A superposed epoch analysis for the aftershocks also reveals similar geomagnetic variations though the amplitude of them is one order of magnitude smaller than that of the main shock. A crustal dynamo mechanism is discussed as a possible cause of such co-seismic geomagnetic variations.
  • T HASHIMOTO, Y TANAKA
    GEOPHYSICAL RESEARCH LETTERS 22 (3) 191 - 194 0094-8276 1995/02 [Refereed][Not invited]
     
    Self-potential (SP) observation was carried out in the summit area of Unzen, one of the active volcanoes in Kyushu island, Japan, We found a positive SP anomaly in the vicinity of the newly extruded lava dome. The potential difference across the anomaly exceeds 1000mV per 500m. Streaming potentials associated with subsurface hydrothermal convection seem to be the most reasonable mechanism for the positive anomaly. In association with the first emergence of the lava dome a sharp increase of SP was detected, which is considered to be a result of the growth of the hydro-thermal system.
  • T. Hashimoto, Y. Tanaka
    Geophysical Research Letters 22 (3) 191 - 194 1944-8007 1995 [Refereed][Not invited]
     
    Self‐potential (SP) observation was carried out in the summit area of Unzen, one of the active volcanoes in Kyushu island, Japan. We found a positive SP anomaly in the vicinity of the newly extruded lava dome. The potential difference across the anomaly exceeds 1000mV per 500m. Streaming potentials associated with subsurface hydrothermal convection seem to be the most reasonable mechanism for the positive anomaly. In association with the first emergence of the lava dome a sharp increase of SP was detected, which is considered to be a result of the growth of the hydro‐thermal system. Copyright 1995 by the American Geophysical Union.
  • Hashimoto, T, T. Kagiyama, F. Masutani
    Bull. Earthq. Res. Inst., Univ. Tokyo 69 257 - 266 1994 [Refereed][Not invited]

MISC

  • アトサヌプリ
    北海道大学大学院理学研究院  令和３年度北海道受託研究「北海道における火山に関する研究」報告書  1  -82  2022/03  [Not refereed][Not invited]
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  • 有珠山
    北海道大学大学院理学研究院  令和２年度北海道受託研究「北海道における火山に関する研究」報告書  1  -90  2021/03  [Not refereed][Not invited]
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  • 渋谷桂一, 橋本武志, 早川智也, 吉川契太郎  北海道大学地球物理学研究報告(Web)  (84)  2021
  • 奥野充, 井口正人, 三好雅也, 三浦大助, 小林淳, 橋本武志, 大場武, 佐藤鋭一, 宝田晋治  火山  66-  (2)  2021
  • 十勝岳
    北海道大学大学院理学研究院  平成30年度北海道受託研究「北海道における火山に関する研究」報告書  1  -96  2020/03  [Not refereed][Not invited]
    Download
  • 青山裕, 田中良, 橋本武志, 村上亮, 成田翔平  北海道大学地球物理学研究報告(Web)  (83)  2020
  • 井上智裕, 橋本武志, 田中良  日本地球惑星科学連合大会予稿集(Web)  2020-  2020
  • 佐藤彰紀, 橋本武志, 早川智也, 吉川契太郎, 小山崇夫  日本地球惑星科学連合大会予稿集(Web)  2020-  2020
  • 宇津木充, 橋本武志, 佐藤彰紀, 多田訓子, 太田豊宣, 吉川慎, 井上寛之  日本地球惑星科学連合大会予稿集(Web)  2020-  2020
  • 早川智也, 吉川契太郎, 橋本武志  日本地球惑星科学連合大会予稿集(Web)  2020-  2020
  • 井上智裕, 橋本武志, 田中良, 山谷祐介  地球電磁気・地球惑星圏学会総会及び講演会(Web)  148th-  2020
  • 橋本武志, 青山裕, 田中良, 大倉敬宏, 森俊哉  日本火山学会講演予稿集  2020-  2020
  • 田中良, 橋本武志, 成田翔平  日本火山学会講演予稿集  2020-  2020
  • 井上智裕, 橋本武志, 田中良, 山谷祐介  日本火山学会講演予稿集  2020-  2020
  • 松島喜雄, 宇津木充, 高倉伸一, 山崎雅, 畑真紀, 橋本武志, 上嶋誠  日本火山学会講演予稿集  2020-  2020
  • 高橋 浩晃, 勝俣 啓, 大園 真子, 橋本 武志, 青山 裕, 酒井 慎一, 松本 聡, 岡田 知己, 小菅 正裕, 寺川 寿子, 飯尾 能久, 中尾 茂, 上嶋 誠, 柴田 智郎, 大津 直, 高井 伸雄, 飯場 正紀, 渡部 要一, 菊地 優, 岡崎 太一郎, 白井 和貴, 西村 裕一, 石川 達也, 高瀬 裕也, 永井 宏, 宮森 保紀, 三宅 弘恵, 松島 信一, 浅野 公之, 重藤 迪子, 卜部 厚志, 前田 宜浩, 石澤 友浩, 廣瀬 亘, 小山内 信智, 山田 孝, 笠井 美青, 檜垣 大助, 風間 基樹, 千木良 雅弘, 渦岡 良介, 竹林 洋史, 木村 誇, 石丸 聡, 岡田 成幸, 内田 賢悦, 有村 幹治, 植松 武是, 多々納 裕一, 梶谷 義雄, 能島 暢呂, 田村 圭子, 中村 洋光, 戸松 誠  自然災害科学総合シンポジウム講演論文集  56-  (56)  21  -26  2019/09/11  [Not refereed][Not invited]
     
    2019年9月11日(水), 於 : キャンパスプラザ京都 第1講義室「平成30年北海道胆振東部地震」とその災害に関する総合調査を実施した。震度７を記録した揺れにより, 同時多発斜面災害と, 北海道全域同時停電(ブラックアウト)が発生し, 複合的な災害となった。震源の深さは約37kmで, 大すべり域はそれより浅い20-25km付近であった。木造家屋の倒壊が多発したむかわ町市街では, 地盤構造による地震波の増幅が見られた。同時多発斜面崩壊は, 近隣の活火山の噴火による降下火砕堆積物が素因となった。札幌市内の地盤液状化地帯では, 極めて軟弱な谷埋盛土層が確認された。地震発生が未明であったことが, 建物倒壊による直接死が出なかったことに関係している可能性がある。ブラックアウトは, 社会経済活動に大きな影響を与えた。
  • 雌阿寒岳
    北海道大学大学院理学研究院  平成30年度北海道受託研究「北海道における火山に関する研究」報告書  1  -77  2019/03  [Not refereed][Not invited]
    Download
  • 井上智裕, 橋本武志  日本火山学会講演予稿集  2019-  2019
  • 橋本武志  日本火山学会講演予稿集  2019-  2019
  • 松島喜雄, 宇津木充, 高倉伸一, 山崎雅, 畑真紀, 橋本武志, 上嶋誠  日本地球惑星科学連合大会予稿集(Web)  2019-  2019
  • 橋本武志, 寺田暁彦, 森俊哉, 田中良  日本地球惑星科学連合大会予稿集(Web)  2019-  2019
  • 青山裕, 橋本武志, 田中良, 大島弘光, 齋藤公一滝, 道下剛史, 奥山哲  日本地球惑星科学連合大会予稿集(Web)  2019-  2019
  • ニセコ
    北海道大学大学院理学研究院  平成29年度北海道受託研究「北海道における火山に関する研究」報告書  1  -44  2018/03  [Not refereed][Not invited]
    Download
  • ドローンによる火山観測
    橋本武志, 寺田暁彦, 森 俊哉  地理  63-  29  -35  2018/02  [Not refereed][Not invited]
  • 田中良, 山谷祐介, 田村慎, 橋本武志, 岡崎紀俊, 高橋良, 茂木透  日本地球惑星科学連合大会予稿集(Web)  2018-  2018
  • 早川智也, 松井博幸, 押野見純司, 橋本武志  日本地球惑星科学連合大会予稿集(Web)  2018-  2018
  • 相澤広記, 上嶋誠, 小山崇夫, 長谷英彰, 山谷祐介, 宇津木充, 神田径, 橋本武志, 塚本果織, 村松弾  日本地球惑星科学連合大会予稿集(Web)  2018-  ROMBUNNO.SEM16‐03 (WEB ONLY)  2018  [Not refereed][Not invited]
  • 橋本武志, 宇津木充, 大倉敬宏, 神田径, 寺田暁彦, 三浦哲, 井口正人  日本地球惑星科学連合大会予稿集(Web)  2018-  ROMBUNNO.SVC41‐04 (WEB ONLY)  2018  [Not refereed][Not invited]
  • 早川智也, 石田時代, 橋本武志, 吉本充宏  建設機械  53-  (6)  1  -8  2017/06  [Not refereed][Not invited]
  • 樽前山
    北海道大学大学院理学研究院  平成28年度北海道受託研究「北海道における火山に関する研究」報告書  1  -51  2017/03  [Not refereed][Not invited]
    Download
  • 電磁気探査（MT/AMT法探査）：火山体内部構造・熱水流動系のモデル化と火山活動度評価手法の高度化（十勝岳）
    田村 慎, 橋本武志, 茂木 透, 山谷祐介, 奥田真央  北海道地質研究所調査研究報告  44-  69  -103  2017/03  [Not refereed][Not invited]
  • 全磁力観測：火山体内部構造・熱水流動系のモデル化と火山活動度評価手法の高度化（十勝岳）
    橋本武志, 青山 裕, 田中 良  北海道地質研究所調査研究報告  44-  105  -111  2017/03  [Not refereed][Not invited]
  • MATSUSHIMA Nobuo, TAKAKURA Shinichi, HATA Maki, UTSUGI Mitsuru, HASHIMOTO Takeshi, UYESHIMA Makoto  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2017-  46  -46  2017
  • 宇津木充, 橋本武志, 城森敦善  日本地球惑星科学連合大会予稿集(Web)  2017-  2017
  • 吉村令慧, 橋本武志, 宮崎真大, 中川潤, 加茂正人, 菅野倖大朗, 高田将仁, 三浦勉, 中本幹大, 荒上夏奈, 山崎健一, 大見士朗, 井口正人  日本地球惑星科学連合大会予稿集(Web)  2017-  2017
  • 田中良, 橋本武志, 松島喜雄, 石戸経士  日本地球惑星科学連合大会予稿集(Web)  2017-  2017
  • HASHIMOTO Takeshi, TANAKA Ryo, UESAWA Shimpei, YAMADA Taishi, HASEGAWA Takeshi, KOZONO Tomofumi, MANNEN Kazutaka, NAKAMICHI Haruhisa, SUMITA Mari, SUZUKI Yuki, TAJIMA Yasuhisa, TAKAGI Akimichi  BULLETIN OF THE VOLCANOLOGICAL SOCIETY OF JAPAN  62-  (4)  189  -196  2017  [Refereed][Not invited]
  • HATA Maki, TAKAKURA Shinichi, MATSUSHIMA Nobuo, HASHIMOTO Takeshi, UTSUGI Mitsuru  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2016-  96  -96  2016
  • 田中良, 橋本武志, 石戸経士, 松島喜雄  日本地球惑星科学連合大会予稿集(Web)  2016-  2016
  • 岡本理沙, 橋本武志  日本地球惑星科学連合大会予稿集(Web)  2016-  2016
  • 相澤広記, 麻植久史, 小池克明, 高倉伸一, 松島喜雄, 畑真紀, 吉永徹, 橋本武志, 宇津木充, 井上寛之, 塩谷太郎, 上嶋誠, 小山崇夫, 神田径, 内田和也, 塚島祐子, 志藤あずさ, 藤田詩織, 若林翌馬, 塚本果織, 松島健, 吉村令慧, 山崎健一, 小松信太郎, 田村慎  日本地球惑星科学連合大会予稿集(Web)  2016-  ROMBUNNO.MIS34‐P26 (WEB ONLY)  2016  [Not refereed][Not invited]
  • 森俊哉, 橋本武志, 寺田暁彦, 篠原宏志, 風早竜之介, 吉本充宏, 田中良  日本地球惑星科学連合大会予稿集(Web)  2015-  2015
  • 三嶋渉, 橋本武志, 茂木透  日本地球惑星科学連合大会予稿集(Web)  2015-  2015
  • 岡本理沙, 橋本武志, 田中良  日本地球惑星科学連合大会予稿集(Web)  2015-  2015
  • HASHIMOTO Takeshi, KANDA Wataru, UTSUGI Mitsuru, ICHIKI Masahiro, KOYAMA Takao  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2015-  (0)  186  -186  2015  [Not refereed][Not invited]
  • Hashimoto Takeshi, Mishima Wataru  Programme and abstracts the Volcanological Society of Japan  2014-  55  -55  2014/11/02
  • Yamaya Yusuke, Takahashi Ryo, Okazaki Noritoshi, Tamura Makoto, Oka Daisuke, Akita Fujio, Mogi Toru, Hashimoto Takeshi, Michishita Takeshi, Tanaka Ryo, Sugano Kotaro, Okuda Mao  Programme and abstracts the Volcanological Society of Japan  2014-  56  -56  2014/11/02
  • Tanaka Ryo, Hashimoto Takeshi, Terada Akihiko  Programme and abstracts the Volcanological Society of Japan  2014-  125  -125  2014/11/02
  • MISHIMA WATARU, HASHIMOTO TAKESHI, MIKI DAISUKE, OSHIMA HIROMITSU  日本火山学会講演予稿集  2014-  148  -148  2014  [Not refereed][Not invited]
  • AOYAMA HIROSHI, MORI HITOSHI, HASHIMOTO TAKESHI, OSHIMA HIROMITSU, MURAKAMI MAKOTO  日本火山学会講演予稿集  2014-  52  -52  2014  [Not refereed][Not invited]
  • AOYAMA HIROSHI, HASHIMOTO TAKESHI, MORI HITOSHI, OSHIMA HIROMITSU, MURAKAMI MAKOTO, USUI YUJI, MIYAMOTO MASASHI  日本火山学会講演予稿集  2013-  33  -33  2013  [Not refereed][Not invited]
  • 中田節也, 森田裕一, 清水洋, 宮町宏樹, 中道治久, 大久保修平, 石原和弘, 中尾茂, 大倉敬宏, 植木貞人, 大島弘光, 上嶋誠, 橋本武志, 野上健治, 森俊哉, 小林哲夫, 宮縁育夫, 下川悦郎, 地頭薗隆, 清水収  自然災害科学総合シンポジウム要旨集  49th-  1  -6  2012/09/11  [Not refereed][Not invited]
  • アトサヌプリ
    北海道大学大学院理学研究院  平成23年度北海道受託研究「北海道における火山に関する研究」報告書  1  -147  2012/03  [Not refereed][Not invited]
    Download
  • 山谷祐介, 本多亮, 茂木透, 長谷英彰, 市原寛, 橋本武志, 上嶋誠  日本火山学会講演予稿集  2012-  2012
  • 相澤広記, 小山崇夫, 上嶋誠, 長谷英彰, 山谷祐介, 橋本武志, 神田径, 小川康雄, 宇津木充, 吉村令慧, 山崎健一  地球電磁気・地球惑星圏学会総会及び講演会予稿集(CD-ROM)  132nd-  ROMBUNNO.A003-10  2012  [Not refereed][Not invited]
  • Aizawa Koki, Yoshimura Ryokei, Yamazaki Ken'ichi, Koyama Takao, Uyeshima Makoto, Hase Hideaki, Yamaya Yusuke, Hashimoto Takeshi, Kanda Wataru, Ogawa Yasuo, Utsugi Mitsuru  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2012-  (0)  2012  [Not refereed][Not invited]
  • Kanda W, Utsugi M, Ogawa Y, Takakura S, Koyama T, Hashimoto T, Komori S, Sonoda T, Sato I, Inoue N  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2012-  (0)  2012  [Not refereed][Not invited]
  • Utsugi M, Kanda W, Hashimoto T, Inoue N, Komori S, Inoue H, Iguchi M  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2012-  (0)  2012  [Not refereed][Not invited]
  • 相澤広記, 小山崇夫, 長谷英彰, 上嶋誠, 橋本武志, 神田径, 小川康雄, 宇津木充, 吉村令慧  物理探査ニュース  (12)  1  -2  2011/10  [Not refereed][Not invited]
  • MOGI Toru, YAMAYA Yusuke, HASHIMOTO Takeshi, AKITA Fujio, SHIBATA Tomoo, TAKAHASHI Tetsuya, TAMURA Shin  物理探査学会学術講演会講演論文集 = Proceeding of the SEGJ Conference  125-  147  -150  2011/09/13
  • 中田節也, 森田裕一, 清水洋, 宮町宏樹, 中道治久, 大久保修平, 石原和弘, 中尾茂, 大倉敬宏, 植木貞人, 大島弘光, 上嶋誠, 橋本武志, 鍵山恒臣, 神田径, 野上健治, 森俊哉, 小林哲夫, 宮縁育夫, 下川悦郎, 地頭薗隆, 清水収  自然災害科学総合シンポジウム要旨集  48th-  1  -6  2011/09/13  [Not refereed][Not invited]
  • OKAZAKI Kenji, MOGI Toru, UTSUGI Mitsuru, YAMAZAKI Takashi, ITO Yoshihiko, HASHIMOTO Takeshi, YAMAYA Yusuke, ITO Hisatoshi, KAIEDA Hideshi, TSUKUDA Kazuhiro, YUKI Yoichi, JOMORI Akira, KUNISHIMA Hideki, TAKAHASHI Yukitsugu  物理探査学会学術講演会講演論文集 = Proceeding of the SEGJ Conference  124-  306  -309  2011/05/10
  • 樽前山
    北海道大学大学院理学研究院  平成22年度北海道受託研究「北海道における火山に関する研究」報告書  1  -35  2011/03  [Not refereed][Not invited]
    Download
  • 橋本武志, 八神樹, 寺田暁彦, 江尻省, 中村卓司, 阿保真, 吉川慎  日本火山学会講演予稿集  2011-  2011
  • Aizawa Koki, Koyama Takao, Hase Hideaki, Uyeshima Makoto, Hashimoto Takeshi, Utsugi Mitsuru, Yoshimura Ryokei, Kanda Wataru, Ogawa Yasuo  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2011-  (0)  23  -23  2011  [Not refereed][Not invited]
  • Hashimoto T, Nakatsuka T, Okuma S, Utsugi M, Koyama T, Kanda W  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2011-  (0)  89  -89  2011  [Not refereed][Not invited]
  • Koyama Takao, Hashimoto Takeshi, Yagami Itsuki, Kanda Wataru, Ogawa Yasuo, Kagiyama Tsuneomi, Utsugi Mitsuru, Yoshimura Ryokei, Yamazaki Ken'ichi, Komatsu Shintaro, Uyeshima Makoto, Hase Hideaki, Aizawa Koki, Yamaya Yusuke, Sugano Takayuki, Watanabe Atsushi, Miyakawa Koji, Maehara Yuki  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2011-  (0)  121  -121  2011  [Not refereed][Not invited]
  • Ejiri Mitsumu K, Nakamura Takuji, Suzuki Hidehiko, Abo Makoto, Hashimoto Takeshi, Terada Akihiko  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2011-  (0)  2011  [Not refereed][Not invited]
  • Ikeba K, Abo M, Hashimoto T, Terada A, Ejiri M, Nakamura T  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2011-  (0)  2011  [Not refereed][Not invited]
  • Magnetic changes on Usu Volcano detected by repeat airborne surveys
    Hashimoto, T, M. Utsugi, T. Nakatsuka, S. Okuma, T. Koyama, W. Kanda, A. Suzuki  Conductivity Anomaly Research  29  -36  2011  [Not refereed][Not invited]
  • Hashimoto, T, T. Mogi, J. Shimizu, T. I  Conductivity Anomaly Research  21  -28  2011  [Not refereed][Not invited]
  • Miyamura, J, N. Okazaki, Y. Fushiya, N. Shigeno, T. Hashimoto  Geophysical Bulletin of Hokkaido University  74-  (74)  1  -19  2011  [Not refereed][Not invited]
     
    We have performed repeat surveys of self-potential (SP) in Tokachidake Volcano since1995, in which some elevated volcanic activity followed the appearance of fumaroles at 62-0Crater. Since thermal anomalies had always preceded to the eruptions at Tokachidake in the last100 years, we expected some temporal and spatial variations of SP anomalies accompanying thethermal activity beneath active craters.Topography-related SP distribution was seen on the northwestern flank in the surveys of1995, 2008 and 2010. This characteristic feature with a gradient of -0.3 mV/m was independentof the survey year and thus thought to be generated from stable flow of ground water. Weassumed that the gradient is uniform over the survey area and corrected the topographic effectprior to the following analyzes in order to emphasize the SP of volcanic origins.We found positive SP anomalies on 62-Craters and Taisho Crater where thermal anomalieshave been seen throughout our SP surveys. These SP anomalies are probably related to thehydrothermal activity beneath the craters but the corresponding electrokinetic current sources shouldnot be very deep since spatial size of these SP anomalies are smaller than a few hundred meters.We also detected temporal variations of SP anomalies corresponding to the thermal activity at62-Craters. The positive SP anomaly on 62-Craters gradually developed toward 1998 up to +100mV, being accompanied by an increase of thermal activity. The anomaly showed a subsequentattenuation down to -50 mV by 2001 in accordance with a decrease of thermal activity. Inaddition, another large positive SP anomaly with an amplitude of approximately +200mV appearednear the active fumaroles on Taisho Crater where fuming was enhanced in 2010. The result ofour SP surveys implies that main thermal activity in the near future may develop at Taisho Craterrather than at 62-Craters. We point that attention should be paid not only to 62-Craters but alsoto Taisho Crater in monitoring the volcanic activity until the next eruption at Tokachidake.
  • 一岡 祐生, 梅原 宏之, 大島 弘光, 橋本 武志, 青山 裕  日本火山学会講演予稿集  2010-  2010/10/09  [Not refereed][Not invited]
  • 阿保 真, 橋本 武志, 中村 卓司  センシングフォ-ラム資料  27-  348  -351  2010/09/27  [Not refereed][Not invited]
  • 宮村淳一, 岡崎紀俊, 伏谷祐二, 重野伸昭, 橋本武志  日本火山学会講演予稿集  2010-  2010
  • 橋本武志, 鈴木敦生, 松本征海  日本火山学会講演予稿集  2010-  2010
  • Kanda W, Tank S. B, Kaya T, Ogawa Y, Kasaya T, Yakiwara H, Ichihara H, Hashimoto T, Koyama T, Utsugi M, Inoue H, Sonoda T  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2010-  (0)  2010  [Not refereed][Not invited]
  • Hashimoto, T, T. Mogi, M. Nishimura, S. Arita  Conductivity Anomaly Research  56  -63  2010  [Not refereed][Not invited]
  • Yamaya, Y, T. Hashimoto, T. Mogi, M. Murakami, N. Okazaki, M. Yoshimoto, Y. Fushiya, M. Hashimoto, T. Yamamoto, M. Nishimura, S. Arita, A. Matoba, R. Tsuchiya  Geophysical Bulletin of Hokkaido University  73-  (73)  281  -294  2010  [Not refereed][Not invited]
     
    Tokachidake Volcano is an active volcano, situated at the SW end of the Daisetsu-Tokachi volcanic chain in the central Hokkaido, Japan. We performed the AMT resistivity survey around the 62 -II crater at the volcano in order to realize the hydrothermal zone, focusing on the recent activity of the crustal inflation and demagnetization beneath the crater. The measured AMT data suggested the three-dimensional structure beneath the study area. Prior to the resistivity modeling, we estimated an effect due to a steep topography in the study area. This estimation clearly showed a strong effect to the apparent resistivity, impedance phase and induction vector. Therefore, the simplified topography was included to the three-dimensional model. The resistivity model supposed by a forward modeling was characterized by a conductor （0.5Ωm） beneath the 62-II crater. We investigated a physical condition which could bring the resistivity of 0.5Ωm, and then estimated that high porosity （0.3）rocks were saturated with hot（～200℃）pore water including dissolved components. Although the origin of hydrothermal water has been unresolved, this result suggests that a hydrothermal zone is developed beneath the 62-II crater.
  • Hashimoto, T, M. Nishimura, S. Arita, T. Yamamoto, M. Ogiso, N. Shigeno, N. Okazaki, T. Mogi  Geophysical Bulletin of Hokkaido University  73-  (73)  269  -280  2010  [Not refereed][Not invited]
     
    We report the recent results of geomagnetic repeat surveys aiming for the detection of subsurface thermal changes at Tokachidake volcano, central Hokkaido, northern Japan. We conducted the first survey in October, 2008. The same pegs and marks were reoccupied in July and September, 2009. During this period a clear dipolar pattern of magnetic changes was detected around the 62-II crater, the present main vent of Tokachidake. This change is quite consistent with the pattern due to a demagnetized sphere placed at a depth of 150 m（1,600 m a.s.l.）beneath the 62-II crater. The change of magnetic moment amounts to 1 - 2×106 Am2. The maximum magnetic change is about 35 nT, overwhelming the errors due to extra-terrestrial changes, secular changes, or seasonal variations. The most likely explanation of this demagnetization is the thermomagnetic effect due to heating beneath the crater. Considering the moderate fumarolic temperature in the 62-II crater, the thermal demagnetization is not caused directly by magma intrusion. We here propose a model that water vapor supplied from depths is releasing latent heat through condensation at the source depth. The heating rate corresponding to the observed magnetic changes is an order of 10 MW. A more speculative suggestion is that water vapor of 107～108 kg/yr is required to realize this heating rate. Considering the fact that fumarolic activity of 62-II crater has somewhat declined since 2006, the ongoing demagnetization may be attributed to the decrease of heat discharge rate from the crater. If this is the case, elevation of heat supply from depths is not necessarily required.
  • Tsuchiya Ryohei, Aoyama Hiroshi, Hashimoto Takeshi, Mori Hitoshi, Oshima Hiromitsu, Suzuki Atsuo, Matoba Atsushi, Ozaki Takeshi  Programme and abstracts the Volcanological Society of Japan  2009-  2009/10/10  [Not refereed][Not invited]
  • 橋本武志, 西村三治, 山本輝明, 有田真, 重野伸昭, 小木曽仁, 岡崎紀俊, 茂木透  日本火山学会講演予稿集  2009-  2009
  • 阿保真, 橋本武志, 中村卓司, 江尻省, 寺田暁彦  リモートセンシングシンポジウム講演論文集  35th-  2009
  • 中村卓司, 太田修史, 橋本武志, 寺田暁彦, 阿保真, 江尻省  リモートセンシングシンポジウム講演論文集  35th-  2009
  • 太田修史, 中村卓司, 寺田暁彦, 橋本武志, 阿保真  大気圏シンポジウム・講演集(Web)  23rd-  2009
  • 広帯域MT観測から推定される阿蘇カルデラの比抵抗構造
    宇津木充, 鍵山恒臣, 小森省吾, 井上寛之, 橋本武志, 小山崇夫, 小川康雄, 神田径, 山崎友也, 長町信吾, 石田 憲久  第4回阿蘇火山の集中総合観測報告書  2009  [Refereed][Not invited]
  • Nakatsuka, T, M. Utsugi, S. Okuma, Y. Tanaka, T. Hashimoto  Conductivity Anomaly Research  108  -114  2009  [Not refereed][Not invited]
  • Yamaya, Y, T. Mogi, H. Hase, H. Yamashita, A. Suzuki, T. Hashimoto  Conductivity Anomaly Research  23  -30  2009  [Not refereed][Not invited]
  • Inner structure of Komezuka scoria cone
    Hashimoto, T, M. Utsugi, S. Komori  Aso volcano, in Report of Joint research program for Aso volcano  43  -55  2009  [Not refereed][Not invited]
  • Takakura, S, T. Hashimoto, Y. Ogawa, H. Inoue, Y. Yamaya, H. Ichihara, T. Mogi, M. Utsugi, N. Matsushima, H. Satoh  Geophysical Bulletin of Hokkaido University  72-  (72)  117  -124  2009  [Not refereed][Not invited]
     
    We conducted magnetotelluric surveys on the eastern flank of Usu Volcano. Analyses of the induction vector and 2-D resistivity inversion along the NNE-SSW direction have been performed. The overall structure of this area is characterized by horizontally stratified resistivity of H-L-H-L from surface to depths. A distinct low-resistivity body lies beneath the Showa-Shinzan lava dome at 2-3 km deep, below which an isolated high-resistivity body has been estimated.
  • Koike, T, H. Hasegawa, I. Fujii, T. Hashimoto  Geophysical Bulletin of Hokkaido University  70-  (72)  107  -115  2009  [Not refereed][Not invited]
     
    We conducted a total field magnetic survey in the 2000 eruption area of Mt Usu. A distinct negative magnetic anomaly was found in the geothermal field in the NW part of the survey area. Meanwhile, no clear magnetic anomaly was found around N-B crater, where active fumaroles were seen. Regarding the negative anomaly in the geothermal field, we performed a 3-D inversion of demagnetized prism model. As a result it has been suggested that the magnetic anomaly is due to the demagnetization at a small depth less than 70 m from the ground surface.
  • Hashimoto, T, Y. Ogawa, S. Takakura, Y. Yamaya, H. Ichihara, M. Utsugi, H. Inoue, T. Koike, H. Hasegawa, T. Mogi  Geophysical Bulletin of Hokkaido University  72-  (72)  79  -105  2009  [Not refereed][Not invited]
     
    In the 2000 eruption of Usu volcano, it is widely believed that magmatic intrusion has reached the shallow subsurface to produce significant ground deformation. We performed a magnetotelluric survey over this area aiming for prospecting the intruded magma. The resistivity section exhibits a High-Low-High three-layered structure. The surface layer with a resistivity around 100 Ωm is likely to correspond with the lower Pleistocene andesite. The second layer is very conductive (0.1 to 1 Ωm), thinning and shallowing in the middle. It is difficult to explain such a low resistivity by anything but the Neogene units containing conductive clay minerals with high salinity ground water. Below it the resistivity gradually increases. The top middle part of the third layer shows the resistivities around 10 Ωm. It looks that this part is pushing the second layer upwards. We investigated whether this block is explainable by intruded magma or not from a viewpoint of the resistivity values. We at first calculated the resistivities of rhyolitic melt by using Gaillard (2004) 's model. The melt resistivities are in a range from 1 to 10 Ωm for 800 to 600 ℃. Secondly, we examined the partial melt by using the MBL model of Schilling et al. (1997). Given that the resistivities of melt and solid are 1 and 10,000 Ωm, respectively, the melt fraction corresponding to the bulk resistivity of 10 Ωm should be 15 vol%. Higher melt resistivity requires a larger melt fraction. The discussion above predicts that the bulk resistivity of the intruded magma will increase by some orders of magnitude in the course of cooling and solidification and that this process can be monitored by MT repeat measurements.
  • Terada Akihiko, Yoshikawa Shin, Hashimoto Takeshi, Kagiyama Tsuneomi, Sasaki Hisashi  Programme and abstracts the Volcanological Society of Japan  2008-  2008/10/10  [Not refereed][Not invited]
  • 樽前山
    北海道大学大学院理学研究院  平成19年度北海道受託研究「北海道における火山に関する研究」報告書  1  -56  2008/03  [Not refereed][Not invited]
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  • 青木陽介, 武尾実, 辻浩, 小山悦郎, 青山裕, 藤松淳, 松本聡, 宮町宏樹, 中道治久, 大倉敬宏, 大湊隆雄, 及川純, 棚田理絵, 筒井智樹, 山本圭吾, 山本希, 山里平, 山脇輝夫, 市原美恵, 井本良子, 風間卓仁, 小山崇夫, 前田裕太, 前野深, 森田裕一, 中田節也, 中村祥, 長田昇, 渡辺秀文, ALANIS P.K.B., ANGGONO T., 藤原善明, 福山由朗, 萩原慎太郎, 橋本武志, 平野舟一郎, 堀口桂香, 飯島聖, 石原吉明, 石川渓太  東京大学地震研究所彙報  83-  (1)  2008
  • 田村慎, 高橋徹哉, 秋田藤夫, 岡崎紀俊, 柴田智郎, 鈴木隆広, 荻野激, 橋本武志, 茂木透  日本火山学会講演予稿集  2008-  2008
  • 神田径, 山崎友也, 橋本武志, 坂中伸也, 山田健太, 小川康雄, 相澤広記, 高倉伸二, 小山崇夫, 小林宰, 小森省吾  第10回桜島火山の集中総合観測 平成19年6月-平成20年3月  89  -104  2008  [Not refereed][Not invited]
  • Kanda, W, T. Hashimoto, T. Hurst, S. Sakanaka, K. Yamada, Y. Ogawa, K. Aizawa, S. Takakura, A. Okubo, T. Koyama, T. Kobayashi, Y. Tanaka, M. Utsugi, H. Inoue, S. Komori, K. Ishihara, Y. Yamazaki, T. Takayama, T. Tameguri  Conductivity Anomaly Research  131  -134  2008  [Not refereed][Not invited]
  • Terada, A, T. Hashimoto  Chikyu Monthly  S60-  (60)  121  -132  2008  [Not refereed][Not invited]
  • YAMAYA Yusuke, HASHIMOTO Takeshi, MOGI Toru  物理探査学会学術講演会講演論文集 = Proceeding of the SEGJ Conference  117-  243  -245  2007/10/01
  • Self-potential survey on usu volcano, 2006 campaign
    Hideaki Hase, Takeshi Hashimoto, Yasunori Nishida, Mitsuru Utsugi, Hiroyuki Inoue, Mizue Saba  Journal of the Hokkaido University, Faculty of Science, Series VII: Geophysics  (70)  43  -52  2007  
    We conducted self-potential (SP) surveys on Usu volcano since July to December 2006. The compiled SP map reveals positive anomalies around Ko-Usu lava dome and at the foot of the volcano, and a negative anomaly on the top of O-Usu lava dome. The SP profile on the summit caldera shows the same pattern of 1985's. However, the peak-to-peak variation of the SP value is different: the 1985's of that shows 1000 mV while the 2006's shows 1400 mV. Topographic effect is clearly shown along the southwestern foot of the volcano, in which coefficient is about -2.5 mV/m. The SP profile corrected of the topographic effect reveals a large and extensive positive anomaly over +600mV and several local positive anomalies over +1000 mV on the summit caldera. The corrected SP also reveals that a positive anomaly at the south part of Ko-Usu lava dome and a negative anomaly at the O-Usu lava dome do not exist. The revealed positive SP anomalies are likely to be affected by an extensive altered layer, located beneath the summit caldera. The largest positive anomaly is shown on the ridge of Usu-Shinzan cryptodome after topographic correction. This anomaly is not regarded to be formed by hydrothermal upwelling, because any indications of fumarolic and geothermal activities have not been observed on the ridge of the volcano. The SP anomaly may be affected by intruded material into the volcano. The SP amplitude in the northwestern part of Nishiyama is very small in spite of rugged topography. An extensive low resistivity layer (< 10 ohm-m) located in the shallow part in the northwestern of Nishiyama probably shields the SP variation.
  • 中村卓司, 橋本武志, 寺田暁彦, 勝部祐一, 佐藤陽介, 津田敏隆, 阿保真  日本気象学会大会講演予稿集  (92)  2007
  • 勝部祐一, 中村卓司, 津田敏隆, 橋本武志, 寺田暁彦  大気圏シンポジウム  21st-  2007
  • 中村卓司, 橋本武志, 寺田暁彦, 杉本尚悠, 勝部祐一, 佐藤陽介, 津田敏隆, 阿保真  地球電磁気・地球惑星圏学会総会及び講演会予稿集(CD-ROM)  122nd-  2007
  • Aeromagnetic anomaly change detected from the Asama Volcano 2005 and 1992 data
    Nakatsuka, T, M. Utsugi, S. Okuma, Y. Tanaka, Joint, group, for, Asama volcano EM experiment, T. Hashimoto  Conductivity Anomaly Research  120  -125  2007  [Not refereed][Not invited]
  • Total magnetic field survey in the Nishiyama crater area of Usu volcano
    Koike, T, H. Hasegawa, I. Fujii, T. Ohwada, T. Tokumoto, T. Ohkawa, T. Hashimoto  Conductivity Anomaly Research  130  -135  2007  [Not refereed][Not invited]
  • Aoyama, H, S. Onizawa, T. Tameguri, A. Suzuki, T. Maekawa, H. Oshima, H. Mori, T. Hashimoto, T. Shiga, H. Koyama, M. Nakahashi, A. Yoshikawa, Y. Fukuyama  Geophysical Bulletin of Hokkaido Universit  70-  (70)  107  -121  2007  [Not refereed][Not invited]
     
    We performed temporary dense observation at Usu volcano in summer 2006, aiming toreveal micro-earthquake activity under the summit crater during dormant period of thevolcanic activity. During about 80 days of temporary observation, more than 330 volcanicearthquakes were observed. Of these earthquakes, well-recorded 142 events are selected forrelocation analysis assuming the 3D-velocity structure model which is a result of theexplosion seismic experiment at Usu volcano in 2001. Following the result of relocation, weestimated focal mechanism of 7 earthquakes whose magnitudes are more than 1.0. Thetemporal observation and analyses gave us three new insights about seismic activity; 1)Continuous activity of volcanic earthquake is seen at the shallow part under the southerncrater floor, 2) Hypocentral regions are distributed along the SW end of the U-shaped faultwhich was built in the 1977-1982 eruption associated with the uplift of Usu-Shinzan cryptdome, 3) Strike direction of the 7 major earthquakes are almost parallel to the U-shaped fault,and dominant mechanism is dip-slip type which suggests subsidence of summit domesrelative to the southern crater floor.
  • Hase, H, T. Hashimoto, Y. Nishida, M. Utsugi, H. Inoue, M. Saba  Geophysical Bulletin of Hokkaido University  70-  (70)  43  -52  2007  [Not refereed][Not invited]
     
    We conducted self-potential (SP) surveys on Usu volcano since July to December 2006.The compiled SP map reveals positive anomalies around Ko-Usu lava dome and at the foot ofthe volcano, and a negative anomaly on the top of O-Usu lava dome. The SP profile on thesummit caldera shows the same pattern of 1985's. However, the peak-to-peak variation ofthe SP value is different: the 1985's of that shows 1000 mV while the 2006's shows 1400 mV.Topographic effect is clearly shown along the southwestern foot of the volcano, in whichcoefficient is about -2.5 mV/m. The SP profile corrected of the topographic effect reveals alarge and extensive positive anomaly over +600mV and several local positive anomalies over+1000 mV on the summit caldera. The corrected SP also reveals that a positive anomaly atthe south part of Ko-Usu lava dome and a negative anomaly at the O-Usu lava dome do notexist. The revealed positive SP anomalies are likely to be affected by an extensive alteredlayer, located beneath the summit caldera. The largest positive anomaly is shown on theridge of Usu-Shinzan cryptodome after topographic correction. This anomaly is notregarded to be formed by hydrothermal upwelling, because any indications of fumarolic andgeothermal activities have not been observed on the ridge of the volcano. The SP anomalymay be affected by intruded material into the volcano. The SP amplitude in the northwestern part of Nishiyama is very small in spite of rugged topography. An extensive lowresistivity layer (< 10 ohm-m) located in the shallow part in the northwestern of Nishiyamaprobably shields the SP variation.
  • Nishida, Y, T. Hashimoto  Geophysical Bulletin of Hokkaido University  70-  (70)  1  -12  2007  [Not refereed][Not invited]
     
    Many researchers have studied the thermal state of the crust and the upper mantle andits tectonic implications in Hokkaido, Japan. Terrestrial heat flow data have revealed thefollowing characteristic features: (1) High heat flow (84〜125 mW/m2) is observed in thebackarc side of the volcanic front, while low heat flow (< 42 mW/m2) is observed in the forearcside, showing the typical thermal aspects of the island arc. (2) The central axis zone ofHokkaido (the Kamuikotan and Hidaka metamorphic belts) shows relatively low heat flow(42〜80 mW/m2). The low heat flow zone extends for Sakhalin. (3) Extremely low (25〜34mW/m2) and high (125 〜210 mW/m2) heat flow is distributed locally on theIshikari-Tomakomai low land and its neighbor on the west, respectively.Based on the heat flow data and other geophysical data, such as the seismic velocitystructure, aeromagnetic data, and so on, the Curie point depth, the solidus temperaturedepth, temperature at the Moho, and the mantle heat flow have been estimated. Theestimated thermal structure implies the temperature of the lower crust comes to the solidustemperature beneath the backarc side of Hokkaido. The result is well supported by theelectrical resistivity soundings: the low resistive layer (10~40 ohm-m) develops in the lowercrust and is ascribed to the effect of partial melting of the crustal rocks.
  • Hashimoto, T, T. Mogi, Y. Nishida, M. Takada, A. Suzuki, T. Maekawa, H. Satoh  Geophysical Bulletin of Hokkaido University  70-  (70)  123  -135  2007  [Not refereed][Not invited]
     
    We investigated geomagnetic changes due to dome-like deformation by using a truncatedcircular cone model. In the case of the normal magnetization, magnetic total field decreasesin the northern side of the uplift center, while it increases in the southern side. We foundthat the original topography prior to the mound formation does not affect the pattern of thismagnetic change. We then apply this calculation to the mound-forming activity in the 2000eruption of Usu Volcano to infer the magnetic change on the foot of the mound. The expectedrange of magnetic total field change at the station U01 is -80 to -800 nT which is in theopposite sense to the observed actual change (+70 nT). We examined some alternativemechanisms to compensate this decrease due to the deformation. None of them, however,can be a promising candidate. The most reasonable explanation so far for this contradictionis the reversed magnetization of the Tertiary lava that may comprise the mound.
  • Terada Akihiko, Sasaki Satoshi, Hashimoto Takeshi, Kagiyama Tsuneomi, Saito Takeshi, Yoshikawa Shin  Programme and abstracts the Volcanological Society of Japan  2006-  2006/10/23  [Not refereed][Not invited]
  • 橋本武志, 池辺伸一郎  日本火山学会講演予稿集  2006-  2006
  • 山谷祐介, 橋本武志, 鈴木敦生, 市原寛, 長谷英彰, 渡辺朋典, 茂木透  日本火山学会講演予稿集  2006-  2006
  • 中村卓司, 杉本尚悠, 津田敏隆, 古本淳一, 阿保真, 橋本武志, 寺田暁彦  日本気象学会大会講演予稿集  (89)  2006
  • Oikawa Jun, Kagiyama Tsuneomi, Tanaka Satoru, Miyamachi Hiroki, Tsutsui Tomoki, Ikeda Yasushi, Katayama Hiroaki, Matsuo Norimichi, Oshima Hiromitsu, Nishimura Yuichi, Yamamoto Keigo, Watanabe Toshiki, Yamazaki Fumihito, Watanabe Hidefumi, Fujii Toshitsugu, Nakada Setsuya, Takeo Minoru, Ohminato Takao, Kaneko Takayuki, Yoshimoto Mitsuhiro, Takeda Toyotarou, Koyama Etsurou, Osada Noboru, Saka Mamoru, Haneda Toshio, Hashimoto Shinichi, Tsuji Hiroshi, Imoto Yoshiko, Matsutani Fumio, Shimano Taketo, Furukawa Akiko, Sagiya Takeshi, Fujii Iwao, Hayashi Yoshinari, Miyajima Rikio, Yamada Mamoru, Okuda Takashi, Itoh Takeo, Hashimoto Takeshi, Maekawa Tokumitsu, Suzuki Atsuo, Itoh Taku, Miura Yasushi, Ueki Sadato, Nishimura Takeshi, Nita Kouichi, Satoh Mineji, Simomura Youichi, Nogami Kenji, Onizawa Sin'ya, Oyamada Hiroko, Funasaki Jun, Chikazawa Shin, Fujiwara Kenji, Hamada Nobuo, Aoki Gen, Takagi Akimichi, Yamamoto Tetsuya, Hayashi Yutaka, Kanao Masaki, Yamashita Mikiya, Shimizu Hiroshi, Watanabe Atsushi, Korenaga Masahiro, Ohkura Takahiro, Yoshikawa Shin, Ikeda Sayaka, Iguchi Masato, Tameguri Takeshi, Yakiwara Hiroshi, Hirano Shuichiro  Bulletin of the Earthquake Research Institute,University of Tokyo  81-  (1)  71  -94  2006  [Not refereed][Not invited]
     
    Fuji volcano (altitude 3,776m) is the largest basaltic stratovolcano in Japan. In late August and early September 2003, seismic exploration was conducted around Fuji volcano by the detonation of 500 kg charges of dynamite to investigate the seismic structure of that area. Seismographs with an eigenfrequency of 2 Hz were used for observation, positioned along a WSW-ENE line passing through the summit of the mountain. A total of 469 seismic stations were installed at intervals of 250-500 m. The data were stored in memory on-site using data loggers. The sampling interval was 4 ms. Charges were detonated at 5 points, one at each end of the observation line and 3 along its length. The first arrival times and the later-phase arrival times at each station for each detonation were recorded as data. P-wave velocities in the surface layer were estimated from the travel time curves near the explosion points, with results of 2.5 km/s obtained for the vicinity of Fuji volcano and 4.0 km5/s elsewhere.
  • NZ・ホワイトアイランド火山における高密度空中磁気観測
    宇津木充, 田中 良和, 橋本武志, Hurst Anthony White, 神田 径, 松島 健, 吉村令慧  空中磁気測量による火山性磁場変動の検出(科学研究費補助金・基盤研究(B)研究成果報告書)  150  -162  2006  [Not refereed][Not invited]
  • 雲仙火山の比抵抗構造から推定されるマグマからの脱ガス
    鍵山恒臣, スリグトモ ワヒュー, 橋本武志, 神田 径, 宗包浩志, 田中良和, 歌田久司, 清水久芳, 宇津木充, 小河 勉, 大湊隆雄  第2回雲仙火山の集中総合観測報告書  32  -44  2006  [Not refereed][Not invited]
  • ホワイトアイランドにおける全磁力連続観測
    神田 径, 橋本武志, 田中良和, 宇津木充, 吉村令慧, ホワイト島火山空中磁気測量チーム  空中磁気測量による火山性磁場変動の検出(科学研究費補助金・基盤研究(B)研究成果報告書)  49  -56  2006  [Not refereed][Not invited]
  • Hase Hideaki, Hashimoto Takeshi, Nishida Yasunori, Utsugi Mitsuru, Inoue Hiroyuki  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2006-  (0)  2006  [Not refereed][Not invited]
  • Hashimoto T, Koike T, Hasegawa H, fujii I, Yamaya Y, Ichihara H, Mogi T, Ogawa Y, Utsugi M, Inoue H, Takakura S, Satoh H  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  2006-  (0)  2006  [Not refereed][Not invited]
  • SAITO TAKESHI, OSAWA SHINJI, HASHIMOTO TAKESHI, TERADA AKIHIKO, YOSHIKAWA SHIN, OKURA TAKAHIRO  日本火山学会講演予稿集  2006-  54  2006  [Not refereed][Not invited]
  • Asama Volcano EM field experiments in 2005
    Hashimoto, T, T. Mogi, A. Suzuki, Y. Yamaya, M. Mishina, T. Nakatsuka, E. Koyama, T. Koyama, K. Aizawa, J. Hirabayashi, M. Matsuo, K. Nogami, Y. Ogawa, N. Ujihara, T. Kagiyama, W. Kanda, A. Okubo, Y. Tanaka, T. Uto, M. Utsugi  Conductivity Anomaly Research  78  -79  2006  [Not refereed][Not invited]
  • Apparent total field change due to secular variation -evaluation of volcanomagnetic effect-
    Hashimoto, T  Conductivity Anomaly Research  51  -58  2006  [Not refereed][Not invited]
  • Zeta-potential measurements of volcanic rocks
    Hashimoto, T, H. Hase, K. Satoh  report of grant-in-aid for scientific research (C) in Japan  8  -16  2006  [Not refereed][Not invited]
  • Repeated ground magnetic survey on White Island Volcano
    Hashimoto, T, W. Kanda, A.W. Hurst, M. Utsugi, R. Yoshimura, Aeromagnetic survey, team on White Island Volcano  report of grant-in-aid for scientific research (B) in Japan  107  -140  2006  [Not refereed][Not invited]
  • Long Valley Caldera -crustal activity in the recent decades-
    Hashimoto, T  Monthly Chikyu  28-  (2)  132  -139  2006  [Not refereed][Not invited]
  • Electrical resistivity survey at the western part of Usu summit caldera - Subsurface structure of faults developed at the 2000 Usu volcano eruption
    Toru Mogi, Takeshi Hashimoto  Journal of the Hokkaido University, Faculty of Science, Series VII: Geophysics  (68)  233  -241  2005/03  
    We carried out electrical resistivity surveys at the western part of Usu summit caldera where many faults developed associating with the 2000 eruption. The faults were found at 30th March, one day before the eruption, and formed resulting in magma ascending just beneath the western part of caldera. A small graben was appeared between a pair of two parallel normal faults in this area. Two survey lines were set across these faults. We measured apparent resistivity of both the Wenner type electrode array and the Eltran array along the survey line at a number of electrode spacing, and made smoothness constrained inversion using both data to obtain the resistivity structure. The resistivity structure revealed the distribution of the resistive Somma Lava layer and the conductive its weathered layer, which is underlain by the resistive recent volcanic ash and secondary sediments layer distributing at the surface. A conductive zone is appeared at the deeper part of fault zone. This may be an alteration zone formed by a thermal water circulation developed around a magma chamber. The resistive surface sediments layer is relatively thicker at the graben, and this means that the faults appeared in the weak zone formed at older time.
  • 田村慎, 岡崎紀俊, 大津直, 橋本武志, 茂木透  日本火山学会講演予稿集  2005-  2005
  • 山谷祐介, 橋本武志, 鈴木敦生, 西田泰典, 市原寛, 茂木透, 渡辺朋典, 渡辺法夫  日本火山学会講演予稿集  2005-  2005
  • 小野構大, 荻原弘尭, 梅原宏之, 橋本武志  日本火山学会講演予稿集  2005-  2005
  • 寺田暁彦, 日野正幸, 竹入啓司, 鈴木敦生, 橋本武志  日本火山学会講演予稿集  2005-  2005
  • 長谷英彰, 石戸経士, 橋本武志, 神田径  日本地熱学会学術講演会講演要旨集  2005-  A14  2005  [Not refereed][Not invited]
  • 口永良部島火山における人工地震探査 —探査の概要と初動の走時について—(共著)
    井口正人, 山本圭吾, 橋本武志, 筒井智樹, 田中 聡, 鬼澤真也, 青木陽介, 渡辺俊樹, 大倉敬宏, 清水 洋, 八木原寛, 宮町宏樹, 平松秀行, 為栗 健, 高山鉄朗, 福嶋麻沙代, Hetty TRIASTUTY, 石原和弘, 大島弘光, 鈴木敦生, 前川徳光, 梶井達矢, 渡辺義明, 萩原庸平, 野上健治, 及川光弘, 平林順一, 辻 浩, 平田安廣, 奥田 隆, 伊藤 拓, 吉川 慎, 井上寛之, 池田さや香, 堀 美緒, 齊藤政城, 平野舟一郎, 上釜友大, 井口元治, 竹下孝弘, 森 健彦  京都大学防災研究所年報  48-  (B)  297  -322  2005  [Not refereed][Not invited]
  • Yamaya, Y, T. Hashimoto, T. Mogi, A. Suzuki, Y. Nishida, N, K. Tanimoto, H. Mori, A. Terada, M. Mishina, H. Hase  Geophysical bulletin of Hokkaido University  68-  (68)  127  -140  2005  [Not refereed][Not invited]
  • Iguchi Masato, Yamamoto Keigo, Hashimoto Takeshi, Tsutsui Tomoki, Tanaka Satoru, Onizawa Shin'ya, Aoki Yosuke, Watanabe Toshiki, Ohkura Takahiro, Shimizu Hiroshi, Yakiwara Hiroshi, Miyamachi Hiroki, Hiramatsu Hideyuki, Tameguri Takeshi, Takayama Tetsuro, Fukushima Masayo, Triastuty Hetty, Ishihara Kazuhiro, Oshima Hiromitsu, Suzuki Atsuo, Maekawa Tokumitsu, Kajii Tatsuya, Watanabe Yoshiaki, Ogiwara Yohei, Nogami Kenji, Oikawa Mitsuhiro, Hirabayashi Junichi, Tsuji Hiroshi, Hiratao Yasuhiro, Okuda Takashi, Itoh Taku, Yoshikawa Shin, Inoue Hiroyuki, Ikeda Sayaka, Hori Mio, Saito Masaki, Hirano Shuichiro, Uekama Yudai, Iguchi Motoharu, Takeshita Takahiro, Mori Takehiko  Bulletin of the Earthquake Research Institute,University of Tokyo  80-  (1)  11  -40  2005  [Not refereed][Not invited]
     
    Seismic exploration using artificial sources was conducted at Kuchierabujima volcano, southwest Japan in November 2004 by 40 participants from 9 national universities andJapan Meteorological Agency to investigate the subsurface seismic structure. The exploration was the 11th joint experiment under the National Project for Prediction of Volcanic Eruptions. A total of 183 temporal stations equippedwith a 2 Hz vertical component seismometer (including 75 3component seismometers) and a portable data logger were deployed on Kuchierabu Island. Dynamite shots with charges of 10-115 kg were detonated at 19 locations, and seismic signals were successfully recorded. To reveal the P-wave velocity structure, 2955 arrival times of the first motion were picked from the seismograms, and 2187 were classified into ranks A and B. From the record sections and the arrival time data, characteristics reflecting the geological structure were identified. Refracted waves of 5 km/s were observed at stations＞5km from the shot points. Apparent velocities near the shot points depend on the surface geology around the shots. P-wave arrived earlier at stations near the summits. Strongly scattered waves were observed similarly near the summits.
  • Hashimoto, T  Bull. Volcanol. Soc. Japan  50-  S115  -S138  2005  [Not refereed][Not invited]
     
    The present paper summarizes the history of applied electromagnetism for field volcanology in Japan and abroad. Achievements are presented especially on volcanomagnetic effect, resistivity structure and its time change, and volcanoelectric effect, with a special attention to the social requirements for eruption prediction. Japan has been one of the leading countries in this research field in the past half century. In particular, geomagnetic filed measurement is recently attracting a growing interest as a regular and standard item for volcano monitoring in this country. Other electric or electromagnetic methods, such as resistivity sounding or selfpotential, have also contributed to reveal shallow processes involving volcanic fluids beneath active volcanoes preceding, during, and after their eruptions. The author also proposes some future directions in developing measurement techniques to improve the spatial coverage, resolution, depth penetration as well as to seek for safer data acquisition.
  • Zeta potential measurements of rock samples (Takano-obane lava) from a boring core
    Hase, H, T. Ishido, T. Hashimoto, K. Furukawa  Conductivity Anomaly Research  48  -53  2005  [Not refereed][Not invited]
  • 長谷 英彰, 石戸 経士, 橋本 武志  Conductivity anomaly研究会論文集  25  -32  2004
  • 橋本 武志, 茂木 透, 西田 泰典  Conductivity anomaly研究会論文集  46  -54  2004
  • 山谷祐介, 茂木透, 橋本武志  日本火山学会講演予稿集  2004-  2004
  • 佐波瑞恵, 茂木透, 橋本武志, 西田泰典, 鈴木敦夫, 高倉伸一, 松島喜雄  日本火山学会講演予稿集  2004-  2004
  • 長谷英彰, 石戸径士, 橋本武志, 長谷中利昭, 三好雅也  日本火山学会講演予稿集  2004-  2004
  • 橋本武志, 赤間秀俊, 前川徳光, 鈴木敦生, 茂木透, 山谷祐介, 西田泰典  日本火山学会講演予稿集  2004-  2004
  • 神田 径, 田中良和, 宇津木 充, 橋本武志, 北田直人, 後藤秀作, 大野正夫  火山爆発のダイナミックス平成15年度研究成果報告書  67  -74  2004  [Not refereed][Not invited]
  • Yamaya, Y, K. Tanimoto, Y. Nishida, M. Saba, M. Miyahara, K. Yoshida, T. Mogi, T. Hashimoto  Geophysical bulletin of Hokkaido University  67-  39  -51  2004  [Not refereed][Not invited]
  • Hashimoto, T, T. Mogi, Y. Nishida, Y. Ogawa, J. Hirabayashi, M, Oikawa, M. Saito, M. Mizuhashi, N. Ujihara, Nurhasan, T. Wakabayashi  Report of the 4th Joint Observation of Kusatsu-Shirane Volcano  133  -142  2004  [Not refereed][Not invited]
  • Hashimoto, T, T. Mogi, Y. Nishida, Y. Ogawa, N. Ujihara, M. Oikawa, M. Saito, Nurhasan, S. Mizuhashi, T. Wakabayashi, R. Yoshimura, A. W. Hurst, M. Utsugi, Y. Tanaka  J. Fac. Sci. Hokkaido Univ., Ser. VII  12-  (2)  97  -113  2004  [Not refereed][Not invited]
  • HURST Tony, TANK S.Bulent  京都大学防災研究所年報. B = Disaster Prevention Research Institute Annuals. B  46-  (0)  729  -737  2003/04/01  [Not refereed][Not invited]
     
    2002年9月, 富士山周辺で広帯域 MT観測を行なった。その結果, 富士山直下深部に低抵抗体が存在することが強く示唆された。現在のところ, データの量, 質とも不十分なため, その低抵抗体の深さや広がりは不明である。しかし予備的な解析によると, 低抵抗体の深さの上面は, 深さ 15キロの深部低周波地震の発生領域と一致するために, マグマ溜りを表している可能性がある。また得られたデータには顕著な異方性が見られる。Wide-band MT soundings in Fuji volcano were carried out September, 2002. Collected data suggestsexistence of low resistivity anomaly deeper part beneath Fuji volcano. A two dimensional inversioncode was applied to data. Preliminary result show that low resitivity body locates at a depth about15-20km which consists with hypo central region of deep low frequency earthquake. This lowresistivity body may be a magma chamber.
  • 地磁気からみた口永良部島火山の蓄熱場
    神田 径, 田中良和, 宇津木 充, 藤井郁子, 橋本武志  地球惑星科学関連学会2003年合同大会予稿集  2003  [Not refereed][Not invited]
  • Hashimoto, T, K. Amita, H. Hase, Y. Tanaka  Hotspring Research Report, Ohita Prefecture  54-  (54)  91  -96  2003  [Not refereed][Not invited]
  • Hashimoto, T, Y. Tanaka, M. J, S. Johnston, M. Utsugi, Y. Sasai, S. Sakanaka  Annuals. Disast. Prev. Res. Inst., Kyoto Univ.  46-  (B)  765  -777  2003  [Not refereed][Not invited]
  • SASAI Y, UYESHIMA M, UTADA H, KAGIYAMA T, ZLOTNICKI J, HASHIMOTO T, TAKAHASHI Y  Programme and abstracts the Volcanological Society of Japan  2002-  (2)  2002/10/22  [Not refereed][Not invited]
  • Sugioka Manabu, Kagiyama Tsuneomi, Sasai Youichi, Uyeshima Makoto, Hashimoto Takeshi  Programme and abstracts the Volcanological Society of Japan  2002-  (2)  2002/10/22  [Not refereed][Not invited]
  • OGAWA Tsutomu, KAGIYAMA Tsuneomi, TANAKA Yoshikazu, HASHIMOTO Takeshi, HASE Hideaki  Programme and abstracts the Volcanological Society of Japan  2002-  (2)  2002/10/22  [Not refereed][Not invited]
  • 中坊真, 小野博尉, 橋本武志, 大倉敬宏, 須藤靖明, 吉川慎, 宇津木充, 坂中伸也, HURST A W  日本火山学会講演予稿集  2002-  107  -107  2002/10/22  [Not refereed][Not invited]
  • 田中 良和, 宇津木 充, 橋本 武志  大分県温泉調査研究会報告  (53)  57  -63  2002/07
  • Sudo Yasuaki, Tsutsui Tomoki, Ono Hiroyasu  Bulletin of the Earthquake Research Institute, University of Tokyo  77-  (4)  303  -336  2002  [Not refereed][Not invited]
     
    A seismic exploration, ASO98, was conducted in Aso Volcano in central Kyushu, Japan. The purpose of this exploration was both to obtain the detailed seismic structures beneath the central cones and to detect the kinematic character of volcanic tremors of Aso Volcano. Six shot points with chemical explosions and a temporary network with 296 seismic stations were deployed over the central cones in a range of 10 km east-west by 9 km north-south. All explosions were completed on 26 November, 1998, and seismic records were successfully acquired at each of 290 stations. This paper reports on the details of ASO98, such as examples of acquired seismic traces for shots, locations of stations and shots, Final first arrival times, amplitude distributions, and examples of records acquired of volcanic tremors. These data are expected to provide much knowledge about volcanic seismology and about Aso Volcano. Further analyses will be described in forthcoming papers.
  • Shallow Structure of the Central Cones of Aso Volcano Inferred from Electromagnetic Explorations
    Hashimoto, T, Y. Tanaka, K. Amita, S. Takakura, W. Kanda, S. Sakanaka, T. Kagiyama  report of grant-in-aid for scientific research in Japan  2002  [Not refereed][Not invited]
  • Nakaboh, M, H. Ono, M. Sako, T. Hashimoto, Y. Sudo, T. Ohkura, S. Yoshikawa, M. Utsugi, S. Sakanaka, A. W. Hurst  Annuals. Disast. Prev. Res. Inst., Kyoto Univ.  45-  (B)  633  -644  2002  [Not refereed][Not invited]
  • Hase, H, S Takakura, T. Ishido, K. Sato, T. Hashimoto, Y. Tanaka, T. Ohkura  Annuals. Disast. Prev. Res. Inst., Kyoto Univ.  45-  (B)  645  -656  2002  [Not refereed][Not invited]
  • Heat Discharging Process and Geomagnetic Changes of Iwoyama, Kuju, Volcano
    Hashimoto, T, M. Utsugi, S. Sakanaka, Y. Tanaka  Annuals. Disast. Prev. Res. Inst., Kyoto Univ.  45-  (B)  617  -625  2002  [Not refereed][Not invited]
  • Preliminary Report on the 2001 Wide-band Magnetotelluric Sounding of Deep Crustal Resistivity Structure in and around the Focal area of the 2000 Tottori-ken Seibu Earthquake, Japan
    The, Research Group for Crustal Resistivity Structure  Annuals. Disast. Prev. Res. Inst., Kyoto Univ.  45-  (B)  489  -497  2002  [Not refereed][Not invited]
  • 田中良和, 宇津木充, 橋本武志, 笹井洋一, 上嶋誠, 後藤忠徳, 坂中伸也, JONSTON M, ZLOTONICKI J  日本火山学会講演予稿集  2001-  70  2001/10/01  [Not refereed][Not invited]
  • 橋本武志, 池辺伸一郎, 田中良和, 小野博尉, 中坊真  日本火山学会講演予稿集  2001-  2001
  • 鈴木隆, 吉川美由紀, 森健彦, 平林順一, 大場武, 須藤靖明, 橋本武志, 迫幹男, LONDONO J  日本火山学会講演予稿集  2001-  2001
  • 橋本武志, 田中良和, 宇津木充, 池辺伸一郎  地球電磁気・地球惑星圏学会総会及び講演会予稿集(CD-ROM)  110th (Web)-  2001
  • Hashimoto, T, Y. Tanaka, M. Utsugi  Annuals. Disast. Prev. Res. Inst., Kyoto Univ.  44-  (B-1)  333  -343  2001  [Not refereed][Not invited]
  • Sakanaka, S, Y. Tanaka, M. Utsugi, T. Hashimoto  Scientific and Technical Reports of Faculty of Engineering and Resource Science., Akita Univ.  22-  25  -38  2001  [Not refereed][Not invited]
     
    Geothermal changes in the subsurface volcanic and geothermal areas can be inferred from monitoring thegeomagnetic changes. We installed several proton precession magnetometers for continuous observation andset up tens of observation sites for repeated survey in the geothermal area at Kuju-Iwoyama, Kyushu Island,Southwest of Japan, after the vapor eruption (phreatic explosion) event in October of 1995. So far, we carriedout repeated surveys three times - in March to April of 1999, August to September of 1999, and Decemberof 1999 to January of 2000 for more than 30 sites. Geomagnetic changes in the total force close to 40nTjyearwere observed at some observation sites during less than one year. The amounts of changes obtained by therepeated surveys were consistent with those obtained by the continuous observations.In this study we indicate that installing a number of sites for repeated survey made it possible to revealthe shape of cooling or heating bodies to some extent. An inclined and cone-shaped cooling body beneathmajor fumaroles is inferred at Kuju-Iwoyama.
  • Heat discharging process and shallow structure of Aso Nakadake crater as inferred from geomagnetic changes
    Hashimoto, T  Proceedings of the research meeting "Volcanic Structure in the Shallow Part and Volcanic Fluid"  149  -159  2001  [Not refereed][Not invited]
  • 笹井洋一, 上嶋誠, 歌田久司, 高橋優志, ZLOTNICKI J, 橋本武志, 宇津木充, 田中良和, 谷元健剛  日本火山学会講演予稿集  2000-  2000
  • Self-potential measurements on the central cones of Aso Volcano
    Hase, H, Y. Tanaka, T. Hashimoto, S. Sakanaka  Annauls. Disast. Prev. Res. Inst., Kyoto Univ.  43-  (B-1)  47  -53  2000  [Not refereed][Not invited]
  • Resistivity sections of the Aso caldera, central Kyushu, Japan, inferred from magnetotelluric soundings
    Takakura, S, T. Hashimoto, K. Koike, Y. Ogawa  Conductivity Anomaly Research  23  -30  2000  [Not refereed][Not invited]
  • Electromagnetic observation during water injection experiment (2)
    Murakami, H, T. Hashimoto, N. Oshiman, S. Yamaguchi  Chikyu Monthly  23-  250  -255  2000  [Not refereed][Not invited]
  • NAKABOH M., ONO H., SAKO M., HASHIMOTO T., SUDO Y.  日本地熱学会学術講演会講演要旨集  1999-  1999/12/01
  • TAKAKURA T., HASHIMOTO T., KOIKE K., OGAWA Y.  日本地熱学会学術講演会講演要旨集  1999-  1999/12/01
  • 茂木透, 橋本武志, 神田径, 田中良和, 山本圭吾, 大羽成征, 大島弘光, 佐波瑞恵, 平林順一  日本火山学会講演予稿集  1999-  53  1999/10/09  [Not refereed][Not invited]
  • AMITA K., HASHIMOTO T., MASUDA H., MORI T., NAKABOU M., YAMAMOTO M., KAWAKATSU H., IDE S., KANESHIMA S., OHMINATO T.  日本地熱学会誌  21-  (1)  76  -76  1999/01/25
  • 長谷英彰, 田中良和, 橋本武志, 坂中伸也  日本火山学会講演予稿集  1999-  1999
  • Kanda W, Mogi T, Munekane H, Ogawa T, Ono H, Sakanaka S, Shimoizumi M, Tanaka Y, Widarto D. S, Amita K, Handa S, Hase H, Hashimoto T, Ikoma Y, Kagiyama T, Koyama T, Masuda H  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  1999-  (0)  134  -134  1999  [Not refereed][Not invited]
  • Hashimoto T, Mogi T, Munekane H, Ogawa T, Ono H, Sakanaka S, Shimoizumi M, Tanaka Y, Djedi S. W, Amita K, Handa S, Hase H, Ikoma Y, Kagiyama T, Kanda W, Koyama T, Masuda H  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  1999-  (0)  1999  [Not refereed][Not invited]
  • Electroseismic changes observed at an explosion experiment in Aso Volcano
    Hase, H, Y. Tanaka, T. Hashimoto, S. Sakanaka, T. Mori, H. Masuda, S. Yoshikawa  Conductivity Anomaly Research  193  -200  1999  [Not refereed][Not invited]
  • Kanda, W, T. Hashimoto, H. Oshima  Annuals. Disast. Prev. Res. Inst., Kyoto Univ.  42-  (B-1)  11  -18  1999  [Not refereed][Not invited]
  • Self-potential on the central cones of Aso Volcano (1)
    Tanaka, Y, T. Hashimoto, H. Hase, S. Sakanaka, H. Masuda  Conductivity Anomaly Research  187  -192  1999  [Not refereed][Not invited]
  • Hashimoto, T, K. Amita, H. Mawatari, Y. Tanaka  Conductivity Anomaly Research  (1999)  29  -37  1999  [Not refereed][Not invited]
  • Hashimoto, T, Y. Tanaka, Y. Nishida, T. Mogi, K. Yamamoto, W. Kanda, J. Hirabayashi, K. Ishihara  Annuals. Disast. Prev. Res. Inst., Kyoto Univ.  42-  (B-1)  19  -25  1999  [Not refereed][Not invited]
  • High-density DC electrical resistivity survey on Sakurajima Volcano
    Mogi, T, T. Hashimoto, W. Kanda, Y. Tanaka, K. Yamamoto, S. Ohba, H. Oshima, M. Saba, J. Hirabayashi  report of cooperative research in Disaster Prevention Research Institute, Kyoto University, 9P-5  103  -108  1999  [Not refereed][Not invited]
  • Selfpotential and magnetic total field surveys on Suwanose-jima volcano
    Kanda, W, S. Mori, T. Hashimoto, H. Oshima  report of the 3rd Joint Observation of Suwanose-jima Volcano  41  -53  1999  [Not refereed][Not invited]
  • Self-poteitial on Sakurajima Volcano
    Hashimoto, T, Y. Tanaka, Y. Nishida, T. Mogi, K. Yamamoto, J. Hirabayashi, K. Ishihara  report of cooperative research in Disaster Prevention Research Institute, Kyoto University  65  -101  1999  [Not refereed][Not invited]
  • Nakaboh M., Sudo Y., Tsutsui T., Yoshikawa M., Garces M., Tanaka Y., Nishijima J., Yoneshige K., Kawaguchi M., Kudou T., Fujimitsu Y., Sako M., Yoshikawa S., Masuda H., Hoka T., Hashimoto T., Diago J. C., Hase H., Ono H.  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  1998-  (0)  64  -64  1998  [Refereed][Not invited]
  • Yoshikawa Shin, Mori Takehiko, Masuda Hideharu, Sako Mikio, Hoka Teruaki, Hashimoto Takeshi, Tsutsui Tomoki, Sudo Yasuaki  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  1998-  (0)  117  -117  1998  [Refereed][Not invited]
  • 伊東市周辺における比抵抗構造調査
    神田 径, 笹井洋一, 歌田久司, 鍵山恒臣, 小山 茂, 小山崇夫, 宗包浩志, 上嶋 誠, 田中良和, 橋本武志, 長谷英彰, 清水久芳, 小河 勉, 網田和宏, 馬渡秀夫  第104回地球電磁気・地球惑星圏学会講演会講演予稿集  (B41-06)  1998  [Not refereed][Not invited]
  • Electromagnetic observations during the water injection experiment at Nojima fault
    Murakami, H, T. Hashimoto, N. Oshiman, N. Sumitomo, S. Yamaguchi, Y. Honkura  Conductivity Anomaly Research  209  -216  1998  [Not refereed][Not invited]
  • Electromagnetic observations during the water injection experiment at Nojima fault
    Murakami, H, T. Hashimoto, N. Oshiman, N. Sumitomo, S. Yamaguchi, Y. Honkura  Monthly Chikyu  S21-  54  -58  1998  [Not refereed][Not invited]
  • Network-MT measurements in Kyushu island
    Tanaka, Y, K. Amita, S. Oba, H. Mawatari, T. Hashimoto, M. Shimoizumi, Y. Sasai  Conductivity Anomaly Research  243  -253  1998  [Not refereed][Not invited]
  • Resistivity structure of Aso caldera inferred from Magnetotelluric measurements (preliminary)
    Takakura, S, T. Hashimoto, Y. Ogawa, T. Nishigaki  Conductivity Anomaly Research  225  -232  1998  [Not refereed][Not invited]
  • Resistivity survey around Nojima fault using earth current
    Hashimoto, T  Monthly Chikyu  S21-  82  -86  1998  [Not refereed][Not invited]
  • Hashimoto, T, Y. Tanaka, T. Mogi, Y. Nishida, S. Oba, K. Yamamoto, K. Ishihara  Annuals. Disast. Prev. Res. Inst., Kyoto Univ.  41-  (B-1)  145  -151  1998  [Not refereed][Not invited]
  • Self-potential measurements on Sakurajima Volcano
    Hashimoto, T, Y. Tanaka, S. Oba, Y. Nishida, K. Tanimoto, M. Utsugi, T. Mogi, K. Yamamoto, K. Ishihara, A. Yamazaki, N. Ito, T. Ikegame  report of the 9th observation project of Sakurajima Volcano  71  -78  1998  [Not refereed][Not invited]
  • HASHIMOTO T., OSHIMAN N., SUMITOMO N., MURAKAMI H., YAMAGUCHI S., HONKURA Y.  日本地震学会講演予稿集 = Programme and abstracts, the Seismological Society of Japan  1997-  (2)  1997/09/15
  • 須藤靖明, 小野博尉, 筒井智樹, 橋本武志, 森健彦, 松本良浩, 中坊真, 増田秀晴, 吉川慎  地球惑星科学関連学会合同大会予稿集  1997-  1997
  • 橋本武志, 田中良和, 大羽成征, 西田泰典, 茂木透, 谷元健剛, 山本圭吾, 石原和弘  日本火山学会講演予稿集  1997-  1997
  • Self-potential variations associated with volcanic eruptions
    Hashimoto, T  Conductivity Anomaly Research  16  -20  1997  [Not refereed][Not invited]
  • 橋本武志, 田中良和, 大羽成征, 茂木透  日本火山学会講演予稿集  1996-  (2)  1996/11/05  [Not refereed][Not invited]
  • 大羽成征, 田中良和, 由佐悠紀, 橋本武志  日本火山学会講演予稿集  1996-  (2)  1996/11/05  [Not refereed][Not invited]
  • 田中良和, 橋本武志, 増田秀晴, 大羽成征, 茂木透  日本火山学会講演予稿集  1996-  (2)  1996/11/05  [Not refereed][Not invited]
  • 中坊真, 西潔, 小野博尉, 迫幹雄, 須藤靖明, 橋本武志  日本火山学会講演予稿集  1996-  1996
  • Nakaboh M., Yusa Y., Kitaoka K., Ohsawa S., Mawatari H., Oue K., Mori T., Kobayashi Y., Sudo Y., Tsutsui T., Hashimoto T., Yoshikawa S., Matsumoto Y., Tanaka M.  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  1996-  (0)  112  -112  1996  [Refereed][Not invited]
  • nakaboh M., Oba S., Tanaka M., Sako M., Hoka T., Masuda H., Yamada T., yoshikawa S., Kobayashi Y., Mogi T., Hashimoto T., Sudo Y., Tutui T., Ono H., Tanaka Y., Kikuchi S., Mori T., Matumoto Y.  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  1996-  (0)  173  -173  1996  [Refereed][Not invited]
  • 日光地域におけるMT観測
    大谷冬彦, 本蔵義守, 松島政貴, 黒木英州, 小川康雄, 光畑裕司, 大志万直人, 坂中伸也, 橋本武志  Conductivity Anomaly研究会1996年論文集  121  -127  1996  [Not refereed][Not invited]
  • Self-potential as an indicator of hydrothermal activity - A case study in 1990-1995 eruption of Unzen Volcano -
    Hashimoto, T  Conductivity Anomaly Research  222  -229  1996  [Not refereed][Not invited]
  • Research on subsurface hydrothermal system using self-potential method
    Tanaka, Y, T. Hashimoto, T. Kagiyama, H. Utada  Research Report of Earthq. Res. Inst., University of Tokyo  12-  7  -9  1996  [Not refereed][Not invited]
  • Electromagnetic Stdies in Kuju-Iwoyama Volcano
    Tanaka, Y, T. Mogi, T. Hashimoto, H. Masuda, T. Yukutake, S. Oba  report of grant-in-aid for scientific research in Japan  125  -140  1996  [Not refereed][Not invited]
  • 森健彦, 須藤靖明, 筒井智樹, 吉川慎, 迫幹雄, 外輝明, 松本良浩, 中坊真, 橋本武志  日本地震学会秋季大会講演予稿集  1995-  1995
  • 橋本武志, 田中良和  日本火山学会講演予稿集  1995-  1995
  • Mori T., Sudo Y., Tsutsui T., Yoshikawa S., Sako M., Hoka T., Matsumoto Y., Nakaboh M., Hashimoto T.  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  1995-  (0)  96  -96  1995  [Refereed][Not invited]
  • 上嶋誠, 歌田久司, 鍵山恒臣, 田中良和, 橋本武志, 増田秀晴, 松島健  雲仙岳における火山体構造探査の事前調査研究 平成6年度 No.06306011  69  -73  1995  [Not refereed][Not invited]
  • Self-potential measurement on the crater lake of Kirishima-Shinmoedake Volcano
    Hashimoto, T, Y. Honkura, F. Ohtani  Conductivity Anomaly Research  23  -30  1995  [Not refereed][Not invited]
  • Hashimoto, T, Joint Research Group of, Universities for, Unzen Volcano  report of grant-in-aid for scientific research in Japan  80  -86  1995  [Not refereed][Not invited]
  • 田中 良和, 橋本 武志, 増田 秀晴, 吉川 慎, 大学合同観測班  京都大学防災研究所年報  (37)  p193  -206  1994/04
  • 田中良和, 橋本武志, 増田秀晴  日本火山学会講演予稿集  1994-  1994
  • 石戸経士, 松島喜雄, 矢野雄策, 中尾信典, 菊地恒夫, 光畑裕司, 内田利弘, 橋本武志  日本火山学会講演予稿集  1994-  1994
  • 橋本武志, 田中良和  日本火山学会講演予稿集  1994-  1994
  • On electrode as a sensor
    Hashimoto, T  Conductivity Anomaly Research  86  -97  1994  [Not refereed][Not invited]
  • Hashimoto, T, Y. Tanaka, Y. Sudo  Annuals Disast. Prev. Res. Inst., Kyoto Univ.  37-  (B1)  183  -191  1994  [Not refereed][Not invited]
  • Volcanic activity and self-potential field of Unzen Volcano
    Hashimoto, T, Joint Research Group of, Universities for, Unzen Volcano  report of grant-in-aid for scientific, research in Japan  90  -102  1994  [Not refereed][Not invited]
  • INOUE Tomohiro, MOTOKI Tomohiro, UTADA Hisashi, KAGIYAMA Tsuneomi, MASUTANI Fumio, YAMAGUCHI Masaru, HASHIMOTO Takeshi  Programme and abstracts the Volcanological Society of Japan  1993-  (2)  1993/10/04  [Not refereed][Not invited]
  • HASHIMOTO Takeshi, TANAKA Yoshikazu, KAGIYAMA Tsuneomi, MASUTANI Fumio  Programme and abstracts the Volcanological Society of Japan  1993-  (2)  1993/10/04  [Not refereed][Not invited]
  • Uyeshima M, Utada H, Kagiyama T, Hashimoto T, Tanaka Y, Magnetotelluric Research, Group of, Unzen Volcano  Programme and abstracts the Volcanological Society of Japan  1993-  (2)  1993/10/04  [Not refereed][Not invited]
  • Hydrothermal convection inferred from self-potential measurements
    Hashimoto, T, Y. Tanaka, H. Masuda, H. Utada, T. Kagiyama, F. Masutani  Conductivity Anomaly Research  249  -255  1993  [Not refereed][Not invited]
  • Hashimoto Takeshi, Tanaka Yoshikazu, Masuda Hideharu, Utada Hisashi, Kagiyama Tsuneomi, Masutani Fumio  Programme and abstracts the Volcanological Society of Japan  1992-  (2)  33  -33  1992/11/09  [Not refereed][Not invited]
  • TANAKA Yoshikazu, HASHIMOTO Takeshi, MASUDA Hideharu  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  1992-  85  -85  1992
  • Miura T., Koyaguchi T., Tanaka Y., Hashimoto T.  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  1992-  82  -82  1992
  • Self-potential measurements on Unzen volcano in 1991
    Hashimoto, T, Y. Tanaka, H. Masuda, H. Utada, T. Kagiyama, F. Masutani  Conductivity Anomaly Research  1992-  249  -256  1992  [Not refereed][Not invited]
  • KAGIYAMA Tsuneomi, UTADA Hisashi, MASUTANI Fumio, YAMAMOTO Tetsuya, MURAKAMI Hideki, MASUDA Hideharu, HASHIMOTO Takeshi, TANAKA Yoshikazu  Programme and abstracts the Volcanological Society of Japan  1991-  (2)  152  -152  1991/10/14  [Not refereed][Not invited]
  • Tanaka Y., Hashimoto T., Masuda H., Handa S., Utada H.  PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN  1991-  24  -24  1991

Books etc

  • Volcanic Lakes
    Hurst T, Hashimoto T, Terada A (ContributorCrater Lake Energy and Mass Balance)
    Springer 2015
  • 日本地方地質誌1 北海道地方
    西田泰典, 橋本武志 (Contributor10.5 北海道における地殻，上部マントルの熱的構造)
    朝倉書店 2010/11
  • The Sun-Earth system science
    HASHIMOTO Takeshi (Joint workChapter 10: Magnetic field of the Earth)
    京都大学学術出版会 2010/05

Presentations

  • Repeated aeromagnetic survey aiming for monitoring the volcanomagnetic effects and 3D imaging of the magnetization changes  [Not invited]
    Hashimoto T, K Shibuya
    IAVCEI  2023/01
  • Persistent cooling remagnetization beneath the summit crater of Usu Volcano  [Not invited]
    Hashimoto, T
    The Volcanological Society of Japan  2022/10
  • A t rial application of the Volcanic Unrest Index (VUI) to Mt. Tokachidake  [Not invited]
    Hashimoto, T, H Aoyama, R Tanaka, T Ohkura, T Mori
    日本火山学会  2020/10
  • From monitoring to forecasting -Toward statistical evaluation of non-magmatic unrest-  [Invited]
    HASHIMOTO Takeshi
    International Workshop on the mechanism of Phreatic Eruption  2020/01
  • 噴気画像の自動処理  [Not invited]
    日本火山学会秋季大会  2019/09
  • Source characteristics of demagnetization and ground deformation during inter-eruptive periods  [Not invited]
    Hashimoto T, Utsugi M, Ohkura T, Kanda W, Terada A, Miura S, Iguchi M
    International Union of Geodesy and Geophysics  2019/07
  • Simple and Fast Method to Remove Volcanic Smoke in Visible and TIR Imagery  [Not invited]
    Hashimoto T, Terada A, Tanaka R
    International Union of Geodesy and Geophysics  2019/07
  • Volcanic gas measurements using UAVs  [Not invited]
    Hashimoto T, Terada A, Mori T, Tanaka R
    Japan Geoscience Union  2019/05
  • On the characterisics of ground deformation and demagnetization in inter-eruptive periods  [Not invited]
    Hashimoto T, Utsugi M, Ohkura T, Kanda W, Terada A, Miura S, Iguchi M
    Japan Geoscience Union  2018/05
  • Importance of multi-parameter monitoring during non-eruptive stage (an example from Mt. Tarume)  [Not invited]
    Hashimoto T, Matsumoto M, Aoyama H, Koyama H, Morii A, Mishima W, Ogino T, Takahashi R, Okazaki N
    The Volcanological Society of Japan  2017/09
  • Long-term Correlation between Geomagnetic Filed Changes, Ground Deformation and Gas Composition at Mt. Tarumae Volcano, Northern Japan  [Not invited]
    Hashimoto, T, Matsumoto, M, Okamoto, R, Koyama, H, Morii, A, Mishima, W, Ogino, T, Takahashi, R, Okazaki, N
    International Association of Volcanology and Chemistry of Earth's Interior  2017/08
  • Volcano-magnetic field changes coincident with ground deformation  [Not invited]
    Hashimoto T, Tanaka R
    The Volcanological Society of Japan  2016/10
  • Detection of Aeromagnetic Field Changes Using an Unmanned Autonomous Helicopter: Repeated Experiments at Tarumae Volcano (Japan)  [Not invited]
    Hashimoto T, Koyama T, Yanagisawa T, Yoshimoto M, Ohminato T, Kaneko T
    American Geophysical Union  2015/12
  • Image processing for plume reduction  [Not invited]
    Hashimoto T, Terada A, Tanaka R
    The Volcanological Society of Japan  2015/09
  • Geomagnetic variations during inter-eruptive at volcanoes with an epithermal system  [Not invited]
    Hashimoto T, Kanda W, Utsugi M, Ichiki M, Koyama T
    The Volcanological Society of Japan  2015/09
  • Long-term volcano-magnetic effects associated with phreatic eruptions  [Not invited]
    Hashimoto, T, Kanda, W, Utsugi, M, Ichiki, M
    International Union of Geodesy and Geophysics, General Assembly  2015/06
  • Re-examination of the geomagnetic changes in the early stage of the Usu 2000 eruption  [Not invited]
    Hashimoto T, Mishima W
    The Volcanological Society of Japan  2014/11
  • Geomagnetic Changes over Tarumae Volcano (Japan) Through Repeated Surveys Using an Unmanned Helicopter  [Not invited]
    Hashimoto T, Koyama T, Yanagisawa T, Yoshimoto M, Kaneko T, Ohminato T, Suzuki E
    Asia Oceania Geosciences Society  2014/07
  • A low-cost SO2 imager with the use of digital cameras of consumer use  [Not invited]
    Hashimoto T, Terada A, Ejiri M, Nakamura T, Makoto Abo M
    International Association of Volcanology and Chemistry of Earth's Interior  2013/07
  • Airborne surveillance using an unmanned autonomous helicopter at Tarumae volcano  [Not invited]
    Hashimoto T, Ohminato T, Kaneko T, Yoshimoto M, Yanagisawa T, Suzuki E, Koyama T, Matsumoto M
    Japan Geoscience Union  2013/05
  • Geomagnetic secular changes in eastern Hokkaido  [Not invited]
    Hashimoto T, Mogi T, Nishimura M, Arita S, Shimizu J, I T, Minamoto Y, Nagamachi S
    Japan Geoscience Union  2012/05
  • Aeromagnetic survey using an unmanned autonomous helicopter over Tarumae volcano  [Not invited]
    Hashimoto T, Koyama T, Kaneko T, Ohminato T, Yoshimoto M, Suzuki E, Yanagisawa T
    Japan Geoscience Union  2012/05
  • Secular changes in total magnetic field in the eastern Hokkaido;evaluation of large-scale variation by using IGRF-  [Not invited]
    Hashimoto T, Mogi T
    Society of Geomagnetism and Earth, Planetary and Space Sciences  2011/11
  • 民生デジタルカメラを利用した簡易SO2カメラの製作  [Not invited]
    橋本武志, 八神 樹, 寺田暁彦, 江尻 省, 中村卓司, 阿保 真, 吉川 慎
    日本火山学会  2011/10
  • Cooling processes following eruptions at Usu volcano, as infrred from aeromagnetic repeat surveys  [Not invited]
    Hashimoto T, Nakatsuka T, Okuma S, Utsugi M, Koyama T, Kanda W
    The Volcanological Society of Japan  2011/10
  • Geomagnetic changes over Usu Volcano detected from aeromagnetic repeat surveys  [Not invited]
    Hashimoto T, Utsugi M, Nakatsuka T, Okuma S, Koyama T, Kanda W, Suzuki A, Joint Group for, Usu Volcano Airborne Magnetic Survey
    Japan Geoscience Union  2011/05
  • Heat accumulation beneath Tokachidake volcano as inferred from total magnetic field change (2)  [Not invited]
    Hashimoto, T, Takahashi Y, Morii A, Shimizu J, I T, Okazaki N, Miyamura J, Joint EM Observation Team for, Tokachidake Volcano
    Society of Geomagnetism and Earth, Planetary and Space Sciences  2010/10
  • Magnetic changes in the summit area of Usu volcano  [Not invited]
    Hashimoto T, Suzuki A, Matsumoto M
    The Volcanological Society of Japan  2010/10
  • Aeromagnetic survey over Usu volcano -plannning and feasibility-  [Not invited]
    Hashimoto T, Utsugi M, Okuma S, Nakatsuka T
    Japan Geoscience Union  2010/05
  • Heat accumulation beneath Tokachidake volcano as inferred from total magnetic field change (2008-2009)  [Not invited]
    Hashimoto T, Nishimura M, Yamamoto T, Arita S, Shigeno N, Ogiso M, Okazaki N, Mogi T
    The Volcanological Society of Japan  2009/10
  • Heat accumulation beneath Tokachidake volcano as inferred from total magnetic field change (2008-2009)  [Not invited]
    Hashimoto T, Nishimura M, Yamamoto T, Arita S, Shigeno N, Ogiso M, Okazaki N, Mogi T
    Society of Geomagnetism and Earth, Planetary and Space Sciences  2009/09
  • On the inner structure and formation process of Komezuka scoria cone, Aso volcano  [Not invited]
    Hashimoto T, Utsugi M, Komori S
    Japan Geoscience Union  2009/05
  • Electric and magnetic changes associated with volcanic processes  [Not invited]
    Hashimoto T
    ASIAN INTERNATIONAL SYMPOSIUM ON MODELING OF VOLCANIC ERUPTION FOR VOLCANIC HAZARD ASSESSMENT  2008/12
  • Resistivity structure across the intrusive zone of the 2000 eruption at Usu volcano  [Not invited]
    Hashimoto, T, Y. Ogawa, S. Takakura, Y. Yamaya, H. Ichihara, T. Mogi
    The 19th International Workshop on EM Induction of the Earth  2008/10
  • Resistivity structure around the intrusion of the 2000 eruption at Usu volcano  [Not invited]
    Hashimoto T, Ogawa Y, Takakura S, Yamaya Y, Ichihara H, Mogi T
    Japan Geoscience Union  2008/05
  • Year-to-year Change in Self-potential on Unzen Volcano  [Not invited]
    Hashimoto, T, Year-to-year Change in Self-potential on, Unzen Volcano
    Cities on Volcano 5  2007/11
  • Continuous Geomagnetic Changes in Usu Volcano  [Not invited]
    Hashimoto T, Suzuki A, Mogi T, Yamaya Y
    Society of Geomagnetism and Earth, Planetary and Space Sciences  2007/09
  • Imaging of the electrical and thermal structure of a shallow magmatic intrusion associated with the 2000 eruption of Usu Volcano  [Not invited]
    Hashimoto, T, Y. Ogawa, S. Takakura, H. Inoue, Y. Yamaya, M. Utsugi, T. Koike, H. Hasegawa, H. Ichihara, H. Satoh, T. Mogi
    International Union of Geodesy and Geophysics  2007/07
  • Geomagnetic changes in the active area of the 2000 eruption of Usu Volcano  [Not invited]
    Hashimoto T, Suzuki A, Maekawa T, Mogi T, Yamaya Y
    Japan Geoscience Union  2007/05
  • Water and heat budget of Yudamari crater lake, Nakadake, Aso (revisited)  [Not invited]
    Hashimoto, T, S. Ikebe
    The Volcanological Society of Japan  2006/10  Aso, Kumamoto
    Download
  • Resistivity survey of Asama Volcano by magnetotellurics, an analysis for the NS line, western summit area  [Not invited]
    Takeshi Hashimoto, Research group for, Asama Volcano, EM field experiment
    Japan Geoscience Union  2006/05  Makuhari, Chiba
    Download
  • 平成17年度浅間山電磁気構造探査の概要  [Not invited]
    橋本武志, 浅間山電磁気構造探査グループ
    浅間山構造探査報告会  2006/03  東京
  • Helicopter-borne magnetic survey over White Island -Is volcanomagnetic effect detectable by repeated survey?-  [Not invited]
    Hashimoto, T, Y. Tanaka, M. Utsugi, A. W. Hurst, R. Yoshimura, W. Kanda, T. Matsushima, B. J. Scott, D. J. Woodward, T. Ohkura, T. Kagiyama, T. Ogawa
    International Symposium on Airborne Geophysics 2006  2006/01  Tsukuba, Ibaraki  Tsukuba, Ibaraki
  • 永年変動によるみかけの全磁力変化－火山地磁気効果の評価－  [Not invited]
    橋本武志
    Conductivity Anomaly研究会  2005/12  東京
  • Ｈ１７年度浅間山電磁気構造探査序報  [Not invited]
    橋本武志, 鈴木敦生, 茂木 透, 山谷祐介, 三品正明, 中塚 正, 小山崇夫, 小山悦郎, 小川康雄, 相沢広記, 氏原直人, 松尾元広, 平林順一, 野上健治, 田中良和, 鍵山恒臣, 宇津木充, 神田 径, 宇都智史, 大久保綾子
    Conductivity Anomaly 研究会  2005/12  東京
  • 橋本武志, 鈴木敦生, 茂木 透, 山谷祐介, 三品正明, 中塚 正, 小山崇夫, 小山悦郎, 小川康雄, 相沢広記, 氏原直人, 松尾元広, 平林順一, 野上健治, 田中良和, 鍵山恒臣, 宇津木充, 神田 径, 宇都智史, 大久保綾子
    東京大学地震研究所第８３３回談話会  2005/11  東京
  • Geomagnetic change due to doming -Re-examination of total field change in the Usu 2000 eruption revisited-  [Not invited]
    Hashimoto, T
    Seciety of Geomagnetism and Earth, Planetary and Space Sciences  2005/09  Kyoto
  • ロングバレー・カルデラ －最近数十年の活動と地磁気観測の目標－  [Not invited]
    橋本武志
    シンポジウム「カルデラの構造と活動そして現在－Out of rangeへの挑戦」  2005/07  熊本
  • A helicopter-borne geomagnetic survey on White Island, New Zealand (FY2004)  [Not invited]
    Hashimoto, T, Y. Tanaka, M. Utsugi, A. W. Hurst, R. Yoshimura, W. Kanda, T. Matsushima, B. J. Scott, D. J. Woodward, T. Ohkura, T. Kagiyama, T. Ogawa
    地球惑星科学関連学会合同大会  2005/05  Makuhari, Chiba, Japan
    Download
  • 自然電位の定量的評価に向けた流動電位実験  [Not invited]
    橋本武志, Annamaria Vicari
    特定領域研究「火山爆発のダイナミクス」シンポジウム  2004/03  東京
  • On the annual variations in geomagnetic differences observed in Long Valley Caldera, California  [Not invited]
    Hashimoto, T, M. J, S. Johnston, Y. Tanaka, Y. Sasai, M. Utsugi, S. Sakanaka
    Inernational Union of Geodesy and Geophysics  2003/06  Sapporo, Japan
  • Heat discharge, water level and geomagnetic changes of the crater lake, Aso Volcano, Japan  [Not invited]
    Hashimoto, T, S. Ikebe, H. Ono, Y. Tanaka
    Western Pacific Geophysics Meeting  2002/07  Wellington, New Zealand
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  • Developing Hydrothermal System and Self-potential Changes Associated with Magma Intrusion  [Not invited]
    Hashimoto, T, Y. Tanaka, T. Kagiyama
    Japan Earth and Planetary Science joint meeting  2002/05  Tokyo
    Download
  • Heat Discharging Process and Geomagnetic changes of Iwoyama, Kuju Volcano  [Not invited]
    Hashimoto, T, M. Utsugi, S. Sakanaka, Y. Tanaka
    Annual meeting of Disaster Prevention Research Institute, Kyoto University  2002/02  Kyoto
    Download
  • Self-potential changes on Unzen Volcano 1991-2001  [Not invited]
    Hashimoto, T, Y. Tanaka, T. Kagiyama
    Unzen Workshop 2002  2002/01  Shimabara
    Download
  • Heat discharge, water level geomagnetic variation observed at Aso Nakadake Volcano  [Not invited]
    Hashimoto, T, Y. Tanaka, M. Utsugi, S. Ikebe
    Seciety of Geomagnetism and Earth, Planetary and Space Sciences  2001/11  Fukuoka
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  • Changes of water level and heat discharge observed at the crater lake of Aso Nakadake  [Not invited]
    Hashimoto, T, S. Ikebe, Y. Tanaka, H. Ono, M. Nakaboh
    Volcanological Society of Japan  2001/10  Kagoshima
    Download

Association Memberships

  • International Association of Volcanology and Chemistry of the Earth's Interior   JAPAN GEOSCIENCE UNION   The Volcanological Scociety of Japan   Society of Geomagnetism and Earth, Planetary and Space Sciences   

Research Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2018/10 -2019/03 
    Author : Takahashi Hiroaki
     
    Comprehensive investigation on the 2018 Hokkaido Eastern Iburi earthquake and its disaster was conducted. Mainshock rupture initiated at deepest part and major slip was occurred in 20-30km deep. Multiple simultaneous landslides in Atsuma town was induced by combination of strong ground shaking and weak sliding layer between pyroclastic fall deposit layers. Halloysite cray minerals was discovered in all sliding layers. Simulation suggested landslides might attack residential houses within 6 seconds. Observed peak ground motions in nearby area were larger than common distance attenuation model. Severe wooden house damage in Mukawa town was due to amplified seismic waves due to site effects. Sounding and boring investigation revealed filled low-density volcanic ash and higher groundwater level in liquefaction area. Electricity blackout caused severe damage in social and economic activities of Hokkaido. These scientific outcomes were explained to residents at public briefing session.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2014/10 -2016/03 
    Author : Yamaoka Koshun, NAKADA Setsuya, MIYAKE Yasuyuki, SUZUKI Takehiko, YAMANAKA Yoshiko, OHKURA Takahiro, MATSUSHIMA Takeshi, NAKAMICHI Haruhisa, OZAWA Taku, TAKEO Minoru, HASHIMOTO Takeshi, MORI Toshiya, TERADA Akihiko, NOGAMI Kenji, SANO Yuji, TADOKORO Keiichi, TAKAGI Akimitsu
     
    In the study of the 2014 eruption of Ontake Volcano we obtained the following results. 1) Regarding the studies on surface change and eruption material, we obtained the aerial and satellite image and laser profile data to compare the topography before and after the eruption. We also clarified the detailed eruption process by the geological survey of the summit area. 2) We clarify the process leading to the phreatic eruption and afterwards by analyzing the existing data set on earthquake and crustal deformation together with the newly obtained data by deploying seismometers. 3) We confirmed that the post-process of the 2014 eruption follows that of the 1979 one by analyzing the volcanic gas that sampled using an unmanned aerial vehicle. 4) In the study of disaster information dissemination, we clarify the preparedness for the volcano disasters in the community around Ontake Volcano.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2012/04 -2015/03 
    Author : HASHIMOTO Takeshi, TERADA Akihiko, MORI Toshiya, NAKAMURA Takuji, EJIRI Mitsumu, ABO Makoto
     
    It has generally been believed that remote-sensing of water (vapor and mist) in volcanic plume is practically very difficult. This research aimed to visualize water content in volcanic plumes as an infrared image via absorption of background solar radiation through the water. Unfortunately this method was proven to be unsuccessful at least in the humid atmospheric conditions in our nation. We, however, improved our low-cost imager of sulfur dioxide gas in volcanic plumes using ultraviolet wavebands. In addition, we made it possible to remotely detect water vapor and water mist separately by using our portable Raman LIDAR system.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2009 -2012 
    Author : KANDA Wataru, HASHIMOTO Takeshi, YAKIWARA Hiroshi, KASAYA Takafumi, OGAWA Yasuo, KOYAMA Takao, UTSUGI Mitsuru, ICHIHARA Hiroshi
     
    In order to clarify the corresponding electrical resistivity structure to the assumed magma reservoir and to the supply paths to Sakurajima volcano and to the submarine volcano, we have conducted the magnetotelluric (MT) measurement mainly along two traverse lines in the direction of WNW-ESE crossing the Aira caldera since 2009. The MT data at 44 sites in total, including 16 seafloor sites, were obtained for the last four years. As a result of 2-D and3-D inversions, a high conductive region extending from the lower crust along the Kagoshima graben was found from the central part of the caldera to the eastern part. This conductor is possibly the structure relevant to the magma supply system.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2010 -2011 
    Author : NAKADA Setsuya
     
    A magmatic eruption event took place at Shinmoedake (Kirishima) Volcano in January 2011, leaving about 300 years of hiatus. Three subplinian explosions occurred on 26 and 27 January, which were followed by 4-day accumulation of lava at the summit crater. Vulcanican explosions were repeated from February to April, and a series of eruptions ended with phreatic explosions which occurred in June and September 2011. This eruption event was preceded by both phreatic explosions in 2008 and 2010 and elevated seismic activity in the regions surrounding Kirishima. GPS observation indicated that significant swelling of the magma chamber which located about 6 km NW of the Shinmoedake crater had continued since the end of 2009. Deflation of the magma chamber accompanied clearly subplinian explosions and the lava accumulation in the crater. The strain-meter observation showed small increases in pressure several tens of minutes prior to the subplinian explosions. Seismic array-observation during a series of vulcanian explosions showed that volcanic tremors occurred beneath the summit crater and between it and the magma chamber, supporting magma's migration from the magma chamber to the crater. The latter was confirmed by the absolute gravity measurement at the place just above the magma chamber. Inflation of the summit area, ncrease in the shallow earthquakes and decrease in the volcanic gas emitted from the crater were observed prior to the vulcanian explosions, strongly implying sealing of the conduit top preceding the explosions. It is considered that magma mixing occurred just before the eruption event because the products of the earliest stage consisted of two magmas with different compositions. The total volume of magma erupted in this event is estimated about 25 million m3, which is about 1/3 volume of the eruption 300 years ago. During this study, we tried two times to make the eruption scenario in which sequences of eruptions are indicated, based on records of eruptions of this volcano 300 years ago and of analogous volcanoes in and outside Japan. No significant mudflows occurred in this eruption event. It is considered that the reason is that the eruption products were mainly of pumice which has high permeability of rain water. Inflation of magma chamber resumed soon after the eruptions in January 2011 and continued by the end of 2011, reaching the same level before the eruption event. It almost stopped in the beginning of 2012, suggesting a halt of the magma supply from depth.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2009 -2011 
    Author : HASHIMOTO Takeshi, NAKAMURA Takuji, TERADA Akihiko, ABO MAKOTO
     
    This study aimed an innovative progress in the remote sensing of volcanic gases by introducing some spectroscopic techniques which have been widely used in the research field of atmospheric science. Followings are the major achievements of this study. (1) Sophistication of the Raman LIDAR system for the water-vapor measurement. This study appended a liquid water channel to the previous instrument, which made separate detection of water vapor and mist in a volcanic plume possible. (2) Development of the high spectrum-resolution LIDAR for the measurement of a temperature profile in a volcanic plume. (3) Fabrication of a low-cost version of the SO2 camera which visualizes the concentration of sulfur dioxide in a volcanic plume.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2006 -2008 
    Author : 橋本 武志, 寺田 暁彦, 中村 卓司, 高橋 幸弘
     
    20年度は, 本研究課題の最終段階として, 2008年10月に再び阿蘇中岳火口でラマンライダーとスペクトルカメラによる噴煙水蒸気観測を行った. 今回は, 前回までの阿蘇での観測と登別大湯沼での観測をふまえ, 火口湖から蒸発する水蒸気と, 噴気口からまとまって放出されている水蒸気とを区別できるように工夫した. 具体的には, ライダーのビームを水平方向にスキャンして, 水平面内での水蒸気分布を求めた, 別途暗視カメラで上昇速度を測定し, 水蒸気フラックスを算出することができた. これにより, 湖面からの蒸発と噴気水蒸気とを区別することができ, 本課題の当初の目標のひとつであった湖面蒸発率の正確な推定を達成することができた. スペクトルカメラについては, 新規の試みであったこともあり, 測定手法の模索に終始したが, 本研究課題によって一定の見通しが得られた. 800nm近辺の赤外吸収帯を用いることにより, 大気水蒸気による吸収の影響を抑えながら, 火山起源の水蒸気による赤外吸収を捉え得ることを実証できた, ただし, 背景光(太陽光)と火山噴煙との位置関係や気象条件による制約が大きいことが問題点として残っている. また, 野外での即時データ処理方法や機器の操作性などの面で, さらに改良すべき点もある. 2008年9月には, 代表者と連携研究者が集まり, 3年間の到達点と今後のステップに向けた改良点について議論した. その結果, 来年度以降もライダーおよびスペクトルカメラを用いた火山ガス研究を発展的に継続することを確認し, さらなる研究目標に必要な装置のスペックに関する青写真を作った.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2005 -2008 
    Author : NAKAGAWA Mitsuhiro, KASAHARA Minoru, HASGIMOTO Takeshi, TAKAHASHI Hiroaki, NISHIMURA Yuichi, YOSHIMOTO Mitsuhiro, KAZAHAYA Kohei, ISHIZUKA Yoshihiro, KANEKO Takayuki
     
    日露米の3ケ国により南千島ウルップ島から北千島パラムシル島で、ビザ無し専門家交流により日露で色丹・国後・択捉島で、火山学的および古津波調査を実施した。その結果、千島列島の過去1万年間の火山噴火履歴と、主要な噴火の噴火様式および特に南千島での津波の発生間隔を検討した。特に火山活動では、9500～6500 年前および4000～1000年前にカムチャッカ～北海道まで大規模な噴火が頻発したこと、またマグマ組成の広域変化が基盤構造の差異と調和的であることを始めて指摘できた。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2003 -2006 
    Author : KAWAKATSU Hitoshi, SUDO Yasuaki, OKURA Takahiro, KANESHIMA Satoshi, YAMAMOTO Mare, HASHIMOTO Takeshi
     
    In order to monitor the volcanic fluid system and to elucidate the mechanism of magma ascent before eruptions, we deployed broadband seismometer and GPS networks in Aso volcano. We also conducted a series of dense array observations to monitor shallow fluid flow activities. As the result, (l) we were successful to observe extremely fast fluid movements in the shallow part of the volcano that appear to indicate a well developed shallow conduit system, (2) we have presented a model that explains the activities of long-period (15s) and short-period (1s) tremors as a result of the activities of a single conduit system of hydrothermal fluid flows. We have also developed an efficient method to compute the dynamic response of a fluid-filled crack that is flexible to many applications which may be encountered in volcano seismology.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2004 -2005 
    Author : HASHIMOTO Takeshi
     
    ζ-potential of several rock samples from various volcanoes was measured by using streaming potential method. Effects of surface conductivity was also taken into accounted for calculating ζ-potential. This procedure is necessary because surface current on the sample cell is not negligible when compared to the current through pore. Pressure gauge has been implemented to the instrumentation system in the second year. In general, ζ-potential of rock samples show strong dependency on pH of the circulating fluid. Four of the seven samples showed positive ζ-potential under the natural condition without pH control. Such rock samples with positive ζ-potential have already been reported by Hase et al. (2004) which measured the ζ-potential of samples from Aso Volcano. The present study has revealed that such 'anomalous' rocks are not very rare. The author investigated the relationship between major elements and ζ-potential of the rock samples in order to elucidate the contributing factors affecting the polarity of the ζ-potential. However, the correlation between each element and ζ-potential does not seem to be very clear. It was suggested that there should be some hidden factor other than the composition of rock sample itself. Further investigation including mineral composition and dissolved component in the fluid is necessary. Another contribution of the present research is the field measurement of electrical resistivity of Tarumae Volcano, Hokkaido. Our magnetotelluric measurement has revealed that there is a very conductive body just beneath the summit crater of the volcano. This result supports the hydrothermal circulation model that is inferred from self-potential anomaly on the volcano.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2003 -2005 
    Author : TANAKA Yoshikazu, HASHIMOTO Takeshi, UTSUGI Mitsuru, KANDA Wataru, KAGIYAMA Tsuneomi, OKURA Takahiro
     
    Four persons made a voyage to White Island of the New Zealand, the proton magnetometer was installed in two points, and ground continuation magnetic field observation was started and also SP measurement was performed in 2003 fiscal year. While five persons made a voyage in the 2004 fiscal year and performing recovery of continuation magnetic field data and ground repetition magnetic field observation, the aero-magnetic survey of the airraid altitudes 50m and 100m was carried out with helicopter. Seven persons made a voyage in the Heisei 17 fiscal year, and the repetition magnetic survey in the ground and the air was carried out. Unfortunately, volcanic activity of the White Island was calm and remarkable magnetic change was not detected. However, the observation technical problem about an air magnetism survey was mostly solved through this research. Namely, the positioning of the flight sensor was achieved with installation of highly precise GPS receiver in the ground and a bird. It asks with an error 1m or less by carrying out differential analysis. It is necessary to detach 40m to avoid the influence of magnetization of a helicopter to the body, and a bird hanging system is excellent in it. The form and cylinder wings of a bird for obtaining a stable flight have been determined. The highly precise cesium magnetometer has owned at the university. The system which displays a GPS position on a PC screen in realtime, and is used for route guidance has been developed. It is also one of the results that it was able to be shown that a flight experiment can be repeated in the volcano in Aso, Kuju, Sakurajima, Bandai, and Asama ignited by this research, and an air magnetic survey can carry out comparatively easily also by the researcher of a university. The subject which especially catches a volcanic magnetic field change by the air magnetic survey which was the big target of this research has been attained by having obtained the result which detects ground observation and a conformable volcanic magnetic field change of 50nT from the analysis of the air magnetism survey data in 1996 in the Kuju volcano, and 2004. These research results presented in the study group of the ISAG2006 air physics inquiry international symposium held in Tsukuba in January, 2006.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2003 -2004 
    Author : 橋本 武志
     
    昨年度採取した火山岩の試料を用いて,流動電位法によるゼータ電位測定を行った.これまでに測定の終わったものは,十勝岳・利尻島・テネリフェ島から採取した7サンプルである.岩石サンプルは0.5mm直径に粉砕し,測定セルに装填した.セルに流動水を通過させたときに両端に生じる電位差を測定することにより,ゼータ電位が測定される. 一般に,岩石のゼータ電位は流動水のpHに対して依存性を示す.今回の測定では,これまでHase(2004)等が示した実験結果と同じく,pH値が大きくなるにつれてゼータ電位が小さくなる傾向が示された.7サンプルのうち,4サンプルが,pH未調整状態の測定で正のゼータ電位を示した.正のゼータ電位を示すサンプルは,Hase(2004)により阿蘇火山でも見つかっているが,今回の測定は,その他の火山でも正のゼータ電位を示す岩石は希ではないことを示唆している.これまで,岩石-水の系では,ゼータ電位は負の値をとるという認識が一般的であったが,それは必ずしも正しくないことが本研究で示された. ゼータ電位の正負を決定している要因について調べるため,岩石の元素組成とゼータ電位の関係を吟味した.その結果は必ずしも明瞭ではなく,主要構成元素の組成だけでゼータ電位が決定されている訳ではないことが示唆された.今後,造岩鉱物組成まで考慮した検討が必要である. 本研究課題でこれまでに得られた成果は,2005年1月に神戸で開かれた本特定領域研究主催の国際シンポジウム「火山爆発研究の基本戦略」で発表したほか,2005年3月に東京で開かれた本特定領域研究の成果報告シンポジウムで発表した.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2001 -2002 
    Author : 橋本 武志
     
    本研究課題では,阿蘇火山をテストフィールドとして,土壌ガス(二酸化炭素)フラックスの分布と自然電位分布の関係を明らかにすることが主たる目的であった. 1.このため,面的測定が容易なチャンバー方式のガスフラックス計を備品として購入した. 2.阿蘇カルデラの周縁部および中央火口丘の一部で,これまで不足していた自然電位分布の測定を補充した.中央火口丘では中岳火口を中心とする高電位異常の他に,湯ノ谷温泉・地獄温泉の両地域では局所的な高電位異常が存在することが明らかになった. 3.カルデラ内で二酸化炭素フラックス計による測定を行ったところ,上記温泉地域では,顕著に二酸化炭素フラックスが高いことが明らかになった.最もフラックスの高かったのは湯ノ谷温泉の噴気口近傍で,800g/m2/day程度の値が計測された.これらのことから,自然電位異常(高電位部分)は熱水の上昇に伴う流動電位である可能性が高い.ただし,高フラックスの領域はそれほど広くなく,むしろ噴気口の周辺に限られていた.阿蘇火山は,近年いくつかの火山で報告されているように山体の広い範囲からじわじわと二酸化炭素が放出されるタイプではないようである. 4.3次元の電場計算コードを開発した.これにより,観測された自然電位マップから等価電流源の強さと位置を推定したところ,中岳火口直下の深さ約1〜2km程度の位置に10A程度の電流源が推定された. 5.中央火口丘のいくつかの地点から岩石をサンプリングし,ζ電位の測定を行った.その結果,高岳・杵島岳周辺の岩石はζ電位が通常とは逆符号の正の値をとることがわかった.この結果は,今後自然電位モデリングを進める上で極めて重要な情報となる.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1999 -2001 
    Author : TANAKA Yoshikazu, SHIMOIZUMI Masaaki, HASHIMOTO Takeshi
     
    Summary of research results The induction vector observed on land in Kyusyu pointed to the southwest. Induction effect of Pacific Ocean could not explain this effect, and existence of high conductive layer in the west part sea area of Kyusyu was pointed out. However little electrical data existed in the west sea area. We notice retired metallic submarine cable laid by NTT, and the electric potential were measured following 5 areas. The data stored in personal computer in each second through 6.5 digits electrometer (Yokogawa 7561 or HP34970A+HP34902A) with the resolution 100uV or 10uV. The computer clock was corrected by GPS. The electrical resistivity beneath the cable was obtained by MT analysis using magnetic data observed at Kanoya. 1) Okimawa area : The coherency to magnetic changes of NS component is very high. R is several 100 to 1000 ohm-m, and uniform in laterally. The results of 1000 ohm-m until 30km support Shimakawa's model, but not show low resistive in deeper part. 2) Kagishima area : The coherency is high to magnetic NS and EW component. R is obtained several 100 to 1000 ohm-m, and not support existence of low resistive zone in deeper part. 3) Koshiki area : R of Kushikino - Naka Koshiki is 10 ohm-m and Naka Koshiki - Satomichi is several 10 ohm-m. They are very low compared with Okinawa and Southern Kagoshima, and not uniform to NS and EW direction. 4) Nagasaki area : High conductive layer is detected in lower crust to upper mantle. The R are 0.3 ohm-m (<100m), 30 ohm-m(<30km), 300 ohm-m (<80km), 3 ohm-m (<80km). 5) Iki area : The results show existence of high conductive layer in lower crust to upper mantle as same as West Nagasaki. The resistivity are 0.3 ohm-m (<1000m), 30 ohm-m (>1km).
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1999 -2000 
    Author : 橋本 武志
     
    雲仙岳山頂部では,1991年より本科研費代表者らを中心として自然電位のモニタリングが行われており,これまでに,溶岩ドーム出現に先立つ急激な電位の上昇や,その後の周辺部での電位低下が捉えられた.これらの現象は熱水対流系の発達過程を電位変化として捉えたものと解釈される.自然電位の長期にわたる変動を観察することは,1991年の噴火で地表付近にセットされた熱源(マグマ)によって熱水対流系がどのような発達過程を遂げるか(その規模や寿命)を推察する有力な手法である.本年度は昨年度に引き続き,山頂部での自然電位繰り返し測定を行った.その結果,以下のことが明らかになった. (1)噴火直後から見られた溶岩ドームを中心とする高電位異常は平成12年度現在も存在する. このことは,一旦発達した対流系(上昇流)が噴火後も基本的には存続していることを意味する. (2)ドームのごく近傍では,緩やかながら依然として電位の上昇が継続している. (3)一方,ドームの南西部(薊谷の北東部)では,昨年度に引き続き,1997頃から電位が低下傾向を示している.この領域は,噴火初期に急激な電位上昇が観察された場所であり,ドーム貫入によって形成された地下の熱水対流系が,周辺部から衰退を始めていることを示唆するものである. 本研究で得られた成果は,2000年6月に東京で開かれたWestern Pacific Geophysics Meeting(合衆国地球物理学会主催)で発表した. また,観測された電位変化を定量的に考察するため,熱水対流と電位計算を結合させた計算機によるシミュレータを開発した.今後,このシミュレータを使って熱水系の発達過程を考察していく予定である.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1997 -2000 
    Author : KAWAKATSU Hitoshi, TSUTSUI Tomoki, KANESHIMA Satoshi, SUDO Yasuaki, OHMINATO Takao, HASHIMOTO Takeshi
     
    Seismic wavefields observed near active volcanoes contain plenty of information about volcanic activities in the frequency range between 0.01 Hz and 1.0 Hz, where, until recently, conventional geophysical monitoring of volcanoes had riot paid much attention except for a few rare cases. The physics operating in a volcano is extremely complex; in different frequency bands, different physical processes dominate the wavefield, which makes broadband seismic observations essential to unravel the physical processes of volcanic activity using seismic data. Deployment of a dense network of broadband seismometers in Aso revealed a hydrothermal reservoir 1 to 1.5 kilometers beneath the crater that is continually resonating with periods as long as 15s, even when there is no apparent surface activity at the crater. When phreatic eruptions are observed, broadband seismograms elucidate vividly the whole eruption process: gradual pressurization and long-period (about 20s) pulsations of the reservoir during the 100-200s before the initiation of the discharge, followed by gradual deflation of the reservoir concurrent with the discharging flow. The observed spatial variation of the signal amplitudes reveals that the source of 15s long period tremors (LPTs) consists of an isotropic expansion (contraction) and an inflation (deflation) of an inclined tensile crack with a strike almost parallel to the chain of craters. The extension of the buried crack plane meets the crater chain, including the active fumarole at the surface, suggesting that the crack has played an important role in transporting steam (gasses) and/or lava to the craters from below. This work also demonstrates a powerful usage of broadband seismometers as geodetic instruments to constrain subsurface structures at active volcanoes.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1997 -1999 
    Author : NISHIDA Yasunori, KAGIYAMA Tsuneomi, TANAKA Yoshikazu, SASAI Yoichi, OGAWA Yasuo, HASHIMOTO Takeshi
     
    Present study has aimed to elucidate the volcano-hydrological environment including the hydrothermal circulation system and to detect the intruded magma by using the geoelectrical methods. For these purposes, we made magnetotelluric observations and self-potential measurements on Usu (dacite magmatism). Miyake-jima (basaltic magmatism) and Hokkaido Komagatake (andesitic magmatism) volcanoes. 1) The common feature of the resistivity structure is seen beneath the three volcanic edifices: The first layer (100m or so) is resistive (about 1000 ohm-m) due to the volcanic rocks and sediments. The second layer is composed of the conductive rocks (several to several tens of ohm-m), suggesting the existence of the ionized water. This layer covers the relatively resistive third layer (several hundreds of ohm-m). The third layer is assumed to be the pre-Tertiary rocks. 2) Positive self-potential anomalies are commonly observed on summit craters (Usu, 400 mV; Miyake-jima, 800 mV; Hokkaido Komagatake, 600 mV). These anomalies can originate from the upwelling of hot groundwater warmed by the heat supplied from deep-seated magma. These findings of hydrothermal circulation are important to consider the magma cooling process. 3) Magnetotelluric soundings on Usu revealed the relatively highly resistive body (400 ohm-m or so) beneath the summit crater. Considering the relation between the resistivity of dacite rock and temperature, and the fumarolic temperature of Usu (500〜600℃, this body is identified as the intruded magma at the time of the 1977-1978 eruptions.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1997 -1998 
    Author : 橋本 武志
     
    本研究では,阿蘇火山における地下浅部熱放出過程を,熱エネルギー収支の観点から理解することを念頭に複合的観測を実施した.以下にその経過と得られた知見をまとめる. まず,活動火口近傍の地磁気連続観測によって火口直下数百m程度の温度状態の監視を行った.これによれば1997年以来継続していた温度低下の傾向が1998年3月を境に温度上昇へと転じている.以下に述べるように自然電位や噴気活動に大きな変動が観測されていないことから,この時期に深部から何らかのエネルギー供給が行われた可能性がある. 地磁気観測と並行して,火口の東南側に電極を配置して自然電位の連続観測を行った.観測当初は雷害により安定したデータが取得できなかったため,電源を太陽電池方式にするなどの処置を施した.この連続観測では研究期間中有意な変動は見られなかった.しかしながら,中央火口丘規模(5km×5km程度)のスケールで自然電位の空間分布を調査したところ,山頂部付近で明瞭な高電位を示すことが明らかになった.従って,阿蘇火山が比較的大規模な熱水対流系を擁していることは確かである. 本研究では,阿蘇火山の噴気にプリュームライズ法を適用して放出熱エネルギー量を見積もる予定であったが,研究期間中の噴気活動は一貫して低調で,この方法の適用に不向きな条件であった.そのため,デジタルビデオカメラを用いた実験の代替地として九重火山を選定した.ビデオ画像をパソコンに取り込んで噴気を追跡し,プリュームライズ法を適用した.カメラを固定して撮影を行えば自動処理による放出工ネルギーのモニタリングも可能であることがわかった.また,この方法によるエネルギー量算出の妥当性を検証するために,別府温泉の噴気を利用してビトー管による直接測定との比較測定を行った.この結果,プリュームライズ法はファクター2程度の誤差で放出エネルギーを見積っていることが明らかとなった.
  • 火山・地熱地域における電磁気現象に関する研究
    Date (from‐to) : 1995
  • Self-potential and hydrothermal circulation in volcanic and geothermal areas Studies on subsurface structure of volcanoes using electromagnetic methods

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