MF研究者総覧

研究者データベース

詳細
researchmap個人ページ
Last Updated :2024/11/06

研究者情報

マスター

アカウント（マスター）

  • 氏名

    橋本　武志(ハシモト　タケシ), ハシモト　タケシ

所属（マスター）

  • 理学研究院　附属地震火山研究観測センター

所属（マスター）

  • 理学研究院　附属地震火山研究観測センター

独自項目

syllabus

  • 2021, 自然史科学特別講義Ⅱ, Special Lecture on Natural History Science II, 修士課程, 理学院, 火山学，地球物理学，地質学，岩石学，地球化学
  • 2021, 自然史科学特別講義Ⅰ, Special Lecture on Natural History Science I, 修士課程, 理学院, 火山学，地球物理学，地質学，岩石学，地球化学
  • 2021, 構造探査学特論, Advanced Subsurface Exploration, 修士課程, 理学院, 地下構造，地震波探査，電磁気探査，MT法，海底観測
  • 2021, 地球計測実習, Exercises in Field Geophysics, 学士課程, 理学部, 地震観測データ解析、津波観測データ解析、多項目測定、地下構造探査データ解析
  • 2021, 地球惑星科学のための電磁気学, Electromagnetism for Earth and Planetary Sciences, 学士課程, 理学部, 電磁気学，地球惑星科学，地磁気，電磁波，放電，プラズマ，電磁場計測方法
  • 2021, 地球惑星電磁気学, Earth and Planetary Electromagnetism, 学士課程, 理学部, 地磁気，岩石磁気，電気伝導度，電離圏，磁気圏，プラズマ，オーロラ

PositionHistory

  • 理学研究院附属地震火山研究観測センター長, 2020年4月1日, 2022年3月31日

researchmap

プロフィール情報

学位

  • 博士（理学）（1996年05月 京都大学）

プロフィール情報

  • 姓

    橋本, ハシモト

  • 名

    武志, タケシ

  • ID各種

    200901000069445606

対象リソース

業績リスト

研究キーワード

  • 地下構造   火口湖   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   地磁気   Volcanology   地球電磁気学   火山物理学   

研究分野

  • 社会基盤（土木・建築・防災） / 防災工学
  • 自然科学一般 / 固体地球科学

経歴

  • 2024年04月 - 現在 文部科学省 科学官（非常勤）
  • 2015年04月 - 現在 北海道大学大学院理学研究院附属地震火山研究観測センター 教授
  • 2007年04月 - 2015年03月 北海道大学大学院理学研究院付属地震火山研究観測センター 准教授
  • 2006年04月 - 2007年03月 北海道大学大学院理学研究院付属地震火山研究観測センター 助教授
  • 2003年03月 - 2006年03月 北海道大学大学院理学研究科附属地震火山研究観測センター 助教授
  • 1997年04月 - 2003年03月 京都大学大学院理学研究科附属地球熱学研究施設 助手
  • 1996年04月 - 1997年03月 京都大学理学部附属火山研究所助手 助手

学歴

  • 1993年04月 - 1996年03月   京都大学   大学院理学研究科   博士後期課程
  • 1991年04月 - 1993年03月   京都大学   大学院理学研究科   博士前期課程
  • 1987年04月 - 1991年03月   京都大学   理学部

委員歴

  • 2021年04月 - 現在   地球電磁気・地球惑星圏学会   評議員
  • 2021年04月 - 現在   地震火山噴火予知研究協議会   研究戦略室員
  • 2021年02月 - 現在   文科省科学技術・学術審議会測地学分科会 火山研究推進委員会   専門委員
  • 2019年02月 - 現在   文科省科学技術・学術審議会測地学分科会地震火山観測研究計画部会（旧：地震火山部会）   専門委員
  • 2017年04月 - 2023年03月   京都大学自然災害研究協議会   委員

受賞

  • 2020年 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年11月 地球電磁気・地球惑星圏学会 大林奨励賞第6号
     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

論文

  • K. Aoyama, T. Hashimoto
    Journal of Geophysical Research: Solid Earth 129 11 2024年10月29日 
    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 2024年07月08日 
    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 2022年08月01日 [査読有り][通常論文]
     
    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年07月 [査読有り][通常論文]
  • Tamura, M, Oka, D, Okazaki, N, Suzuki, K, Hashimoto, T, Mogi, T
    Geothermics 105 102496 - 102496 2022年06月 [査読有り][通常論文]
  • 橋本武志
    火山 67 4 489 - 500 2022年 [査読有り]
  • 橋本武志
    地学雑誌 130 6 771 - 781 2021年12月 [査読有り][通常論文]
  • Tanaka R, Yamaya Y, Tamura M, Hashimoto T, Okazaki N, Takahashi R, Mogi T
    Earth, Planets and Space 73 1 172  2021年08月 [査読有り][通常論文]
     
    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  2020年05月07日 [査読有り][通常論文]
     
    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 2019年06月 [査読有り][通常論文]
     
    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.
  • 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
    火山 64 2 103 - 119 2019年04月 [査読有り][通常論文]
  • 井上智裕, 橋本武志
    北海道大学地球物理学研究報告 82 82 25 - 38 2019年03月 [査読無し][通常論文]
  • Ryo Tanaka, Takeshi Hashimoto, Nobuo Matsushima, Tsuneo Ishido
    Earth, Planets and Space 70 1 72  2018年12月01日 [査読有り][通常論文]
     
    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 2018年07月 [査読有り][通常論文]
     
    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 2018年07月 [査読有り][通常論文]
     
    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年07月 [査読有り][招待有り]
  • Terada A, Morita Y, Hashimoto T, Mori T, Ohba T, Yaguchi M, Kanda W
    Earth Planets Space 70 64  2018年04月 [査読有り][通常論文]
     
    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.
  • 橋本武志, 青山 裕, 小山 寛, 森井敦司, 三嶋 涉, 荻野 激, 高橋 良, 岡崎紀俊
    月刊地球 40 3 163 - 169 2018年 [査読無し][通常論文]
  • Akihiko Terada, Takeshi Hashimoto
    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 122 8 6108 - 6130 2017年08月 [査読有り][通常論文]
     
    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."
  • 十勝岳における電磁気探査 —山体横断MT探査および火口近傍AMT探査—
    田村 慎, 岡崎紀俊, 高橋 良, 橋本武志, 奥田真央, 菅野倖大朗, 早川美土里, 髙田将仁, 橋本政樹, 三嶋 渉
    2017年CA研究会論文集 16 - 23 2017年03月 [査読無し][通常論文]
  • Yoshiya Usui, Yasuo Ogawa, Koki Aizawa, Wataru Kanda, Takeshi Hashimoto, Takao Koyama, Yusuke Yamaya, Tsuneomi Kagiyama
    GEOPHYSICAL JOURNAL INTERNATIONAL 208 3 1359 - 1372 2017年03月 [査読有り][通常論文]
     
    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 2017年03月 [査読有り][通常論文]
     
    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.
  • Yamaya Y, Mogi T, Honda R, Hase H, Hashimoto T, Uyeshima M
    Geochem. Geophys. Geosys. 18 2 735 - 754 2017年02月 [査読有り][通常論文]
     
    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.
  • 畑 真紀, 松島 喜雄, 高倉 伸一, 宇津木 充, 橋本 武志, 上嶋 誠
    日本火山学会講演予稿集 2017 47 - 47 特定非営利活動法人 日本火山学会 2017年
  • 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 2017年01月 [査読有り][通常論文]
     
    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 2017年01月 [査読有り][通常論文]
     
    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 2016年11月 [査読有り][通常論文]
  • Maki Hata, Shinichi Takakura, Nobuo Matsushima, Takeshi Hashimoto, Mitsuru Utsugi
    GEOPHYSICAL RESEARCH LETTERS 43 20 10720 - 10727 2016年10月 [査読有り][通常論文]
     
    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 2016年04月 [査読有り][通常論文]
     
    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.
  • 北海道有珠山，十勝岳におけるMT探査（序報）
    田村 慎, 岡崎紀俊, 高橋 良, 岡 大輔, 秋田藤夫, 奥田真央, 橋本武志, 菅野倖大朗, 茂木 透, 山谷祐介, 藤松 淳, 長山泰淳, 道下剛史
    2016年CA研究会論文集 84 - 89 2016年03月 [査読無し][通常論文]
  • 田中 良, 橋本武志, 鈴木敦生
    北海道大学地球物理学研究報告 79 15 - 23 北海道大学大学院理学研究院 2016年03月 [査読無し][通常論文]
     
    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 2016年03月 [査読有り][通常論文]
     
    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年01月01日 [査読有り][通常論文]
     
    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.
  • 火山地磁気効果と水蒸気噴火
    橋本武志
    2015年CA研究会論文集 75 - 81 2015年 [査読無し][通常論文]
  • 磁場変換関数データによる九州地方の広域比抵抗構造の推定
    畑 真紀, 上嶋 誠, 半田 駿, 下泉政志, 田中良和, 橋本武志, 鍵山恒臣, 歌田久司, 宗包浩志, 市來雅啓, 藤田清士
    2015年CA研究会論文集 18 - 20 2015年 [査読無し][通常論文]
  • 三嶋 渉, 橋本武志, 茂木 透, 森山多加志, 仰木淳平, 森永健司
    北海道大学地球物理学研究報告 78 78 69 - 82 北海道大学大学院理学研究院 2015年 [査読無し][通常論文]
     
    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 2014年03月 [査読有り][通常論文]
     
    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.
  • 橋本武志, 小山崇夫, 大湊隆雄, 金子隆之, 柳澤孝寿, 吉本充宏, 鈴木英一
    2014年CA研究会論文集 92 - 99 CA研究グループ 2014年 [査読無し][通常論文]
  • 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 2014年01月 [査読有り][通常論文]
     
    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 2013年07月 [査読有り][通常論文]
     
    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.
  • 神田 径, 小川康雄, 高倉伸一, 小山崇夫, 橋本武志, 小森省吾, 園田忠臣, 佐藤 泉, 井上直人, 宇津木充
    2013年CA研究会論文集 139 - 144 CA研究グループ 2013年 [査読無し][通常論文]
  • 橋本武志, 小山崇夫, 金子隆之, 大湊隆雄, 柳澤孝寿, 吉本充宏, 鈴木英一
    2013年CA研究会論文集 81 - 87 CA研究グループ 2013年 [査読無し][通常論文]
  • 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 2013年 [査読有り][通常論文]
     
    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 2013年 [査読有り][通常論文]
     
    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
    火山 58 1 251 - 267 特定非営利活動法人 日本火山学会 2013年 [査読有り][通常論文]
     
    2007年11月,第7次火山噴火予知計画の一環として,桜島火山の山麓でAMT法比抵抗構造調査を実施した.南岳山頂火口および昭和火口では,ブルカノ式噴火が繰り返し発生するため,山頂付近へ近づくことができない.そこで我々は,山体の北,西,南東山麓にそれぞれ測線を設定し,合計27観測点で周波数1〜10400Hzの電磁場データを取得した.データは,2Hz以上の周波数帯で概ね良好であった.まず,各測線で得られたデータに対して2次元解析を行った.しかしながら,インピーダンスから推定される構造走向は,全ての測線においてほぼ南北方向を示し,2次元解析は不適当であることが判明したことから,全てのデータを矛盾なく説明するために,3次元解析を行った.3次元モデリングの結果明らかとなった桜島の浅部比抵抗構造は,以下のような特徴を持つ.表層は溶岩層に対応する高比抵抗層で数百から数千Ωmの比抵抗値を示す.その下には,海水や地下水を含む層であると解釈される数Ωm以下の低比抵抗層が続く.基盤構造は,桜島の北部の一部を除いて明瞭ではなく,2層目の低比抵抗層が厚く分布している.表層の高比抵抗層と2層目の低比抵抗層との境界は,概ね海水準付近にあるが,ハルタ山溶岩ドームや鍋山軽石丘などの一部地域の下では,海水準より下に位置する.それらの地域では,過去の噴火に関係した破砕帯が形成されていると考えられる.また引ノ平溶岩ドームから大正火口にかけての地下では,逆に低比抵抗層が地表近くまで盛り上がっており,熱水系の存在が示唆された.一方で,同じ大正噴火の際に溶岩流を流出させた鍋山の縁に位置する火口付近では,そのような低比抵抗層の盛り上がりは見られず,既に熱源が存在しないことを暗示している.
  • Akihiko Terada, Takeshi Hashimoto, Tsuneomi Kagiyama
    BULLETIN OF VOLCANOLOGY 74 3 641 - 655 2012年04月 [査読有り][通常論文]
     
    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.
  • 橋本武志, 茂木 透, 西村三治, 有田 真, 清水淳平, 井 智史, 源 泰拓, 長町信吾
    北海道大学地球物理学研究報告 75 75 117 - 132 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） 2012年03月 [査読無し][通常論文]
     
    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.
  • 橋本武志, 小山崇夫, 金子隆之, 大湊隆雄, 吉本充宏, 鈴木英一, 柳澤孝寿
    北海道大学地球物理学研究報告 75 145 - 159 2012年03月 [査読無し][通常論文]
  • 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 2012年 [査読有り]
     
    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.
  • 橋本武志, 寺田暁彦, 江尻 省, 中村卓司, 阿保 真
    火山 57 4 219 - 225 2012年 [査読有り][通常論文]
  • 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 2011年 [査読有り][通常論文]
     
    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年 [査読有り][通常論文]
  • 山谷 祐介, 笹井 洋一, 竹内 昭洋, 茂木 透, Alanis Paul, Cordon Jr Juan, 橋本 武志, 長尾 年恭
    日本火山学会講演予稿集 2011 90 - 90 特定非営利活動法人 日本火山学会 2011年
  • 小山 崇夫, 金子 隆之, 大湊 隆雄, 渡邉 篤志, 武尾 実, 柳澤 孝寿, 橋本 武志, 本多 嘉明
    日本火山学会講演予稿集 2011 22 - 22 特定非営利活動法人 日本火山学会 2011年
  • 電磁気的手法によるタール火山の監視（SATREPS-Project 2010-2014）
    長尾年恭, 竹内昭洋, 笹井洋一, 山谷祐介, 橋本武志, 茂木 透, 田中良和, P.K. Alanis, J.M. Cordon Jr, J. Sabit, J.S. Sincioco
    ＣＡ研究会論文集 2011 20 - 20 2011年 [査読無し][通常論文]
  • 中塚 正, 大熊茂夫, 有珠山空中磁気探査グループ
    CA研究会論文集 2011 37 - 43 CA研究グループ 2011年 [査読無し][通常論文]
  • 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 2010年01月 [査読有り][通常論文]
     
    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 2009年11月 [査読有り][通常論文]
     
    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 2009年11月 [査読有り][通常論文]
     
    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 2009年11月 [査読有り][通常論文]
     
    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.
  • 長谷英彰, 橋本武志, 西田泰典, 宇津木充, 井上寛之, 佐波瑞恵
    日本地熱学会誌 31 1 27 - 37 2009年 [査読有り][通常論文]
     
    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 2008年11月 [査読有り][通常論文]
     
    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 2008年10月 [査読有り][通常論文]
     
    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 2008年07月 [査読有り][通常論文]
     
    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 2008年06月 [査読有り][通常論文]
     
    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
    北海道大学地球物理学研究報告 71 49 - 59 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） 2008年03月 
    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.
  • 斎藤武士, 大沢信二, 橋本武志, 寺田暁彦, 吉川 慎, 大倉敬宏
    日本地熱学会誌 30 2 107 - 120 2008年 [査読有り][通常論文]
     
    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 2008年 [査読有り][通常論文]
     
    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 2007年10月 [査読有り][通常論文]
     
    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年03月30日 [査読無し][通常論文]
  • 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 2007年02月 [査読有り][通常論文]
     
    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 2007年 
    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 2007年 
    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年 [査読有り][通常論文]
  • 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 86 - 88 CA研究グループ 2006年 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • 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年07月 [査読有り][招待有り]
  • 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 2005年06月 [査読有り][通常論文]
     
    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 2005年05月 [査読有り][通常論文]
     
    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 2005年03月 
    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
    北海道大学地球物理学研究報告 68 233 - 241 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） 2005年03月
  • 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年 [査読無し][通常論文]
  • AW Hurst, PC Rickerby, BJ Scott, T Hashimoto
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 136 1-2 53 - 70 2004年08月 [査読有り][通常論文]
     
    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年
  • 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年
  • H Hase, T Ishido, S Takakura, T Hashimoto, K Sato, Y Tanaka
    GEOPHYSICAL RESEARCH LETTERS 30 23 2003年12月 [査読有り][通常論文]
     
    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 2003年04月 [査読有り][通常論文]
     
    [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.
  • 長谷英彰, 石戸経士, 橋本武志, 神田径, 佐藤佳子
    京都大学防災研究所年報 46B 787-795 - 795 2003年04月 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • Y Sasai, M Uyeshima, J Zlotnicki, H Utada, T Kagiyama, T Hashimoto, Y Takahashi
    EARTH AND PLANETARY SCIENCE LETTERS 203 2 769 - 777 2002年10月 [査読有り][通常論文]
     
    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年 [査読有り][通常論文]
  • 山口 覚, 首藤史朗, 橋本武志, 村上英記, 高木典子
    地震 55 2 143 - 151 日本地震学会 2002年 [査読有り][通常論文]
  • 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年 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • H Murakami, T Hashimoto, N Oshiman, S Yamaguchi, Y Honkura, N Sumitomo
    ISLAND ARC 10 3-4 244 - 251 2001年09月 [査読有り][通常論文]
     
    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 2001年09月 [査読有り][通常論文]
     
    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.
  • 笹井洋一, 上嶋 誠, 歌田久司, 鍵山恒臣, Zlotniki,Jacques, 橋本武志, 高橋優志
    地学雑誌 110 2 226 - 244 学術雑誌目次速報データベース由来 2001年 [査読有り][通常論文]
     
    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.
    日本火山学会講演予稿集 2001 110 - 110 特定非営利活動法人 日本火山学会 2001年
  • 笹井 洋一, 上嶋 誠, 歌田 久司, 鍵山 恒臣, 橋本 武志, 高橋 優志
    地学雑誌 110 2 Plate7 - Plate8 Tokyo Geographical Society 2001年 [査読無し][通常論文]
  • 西田 泰典, 茂木 透, 佐藤 秀幸, 谷元 健剛, 佐波 瑞恵, 高田 真秀, 田中 良和, 橋本 武志, 宇津木 充, 笹井 洋一
    日本火山学会講演予稿集 2000 173 - 173 特定非営利活動法人 日本火山学会 2000年
  • 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
    東京大学地震研究所彙報 74 267 - 285 1999年 [査読無し][通常論文]
  • Sudo, Y, H. Ono, A. W, Hurst, T. Tsutsui, T. Mori, M. Nakaboh, Y. Matsumoto, M. Sako, S. Yoshikawa, M. Tanaka, Y. Kobayashi, T. Hashimoto, T. Hoka, Y. Yamada, M. Masuda, K. Kikuchi
    J. Volcanol. Geotherm. Res. 81 3-4 245 - 267 1998年05月 [査読有り][通常論文]
     
    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 1997年 [査読有り][通常論文]
     
    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 1997年 [査読有り][通常論文]
     
    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年 [査読無し][通常論文]
  • T Iyemori, M Takeda, A Saito, T Araki, T Hashimoto, Y Tanaka
    JOURNAL OF GEOMAGNETISM AND GEOELECTRICITY 48 10 1219 - 1232 1996年 [査読有り][通常論文]
     
    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 1996年 [査読有り][通常論文]
     
    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 1995年02月 [査読有り][通常論文]
     
    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 1995年 [査読有り][通常論文]
     
    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年 [査読有り][通常論文]

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年03月 [査読無し][通常論文]
    ダウンロード
  • 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年03月 [査読無し][通常論文]
    ダウンロード
  • 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年
  • 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年
  • 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年03月 [査読無し][通常論文]
    ダウンロード
  • 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年
  • 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年
  • 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年
  • 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年
  • 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年
  • 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年
  • 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年
  • 田中良, 橋本武志, 成田翔平 日本火山学会講演予稿集 2020 2020年
  • 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年
  • 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年
  • 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年09月11日 [査読無し][通常論文]
     
    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年03月 [査読無し][通常論文]
    ダウンロード
  • 井上智裕, 橋本武志 日本火山学会講演予稿集 2019 2019年
  • 橋本武志 日本火山学会講演予稿集 2019 2019年
  • 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年
  • 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年
  • 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年
  • 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年03月 [査読無し][通常論文]
    ダウンロード
  • 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年02月 [査読無し][通常論文]
  • 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年
  • 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年
  • 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年 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • 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年06月 [査読無し][通常論文]
  • 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年03月 [査読無し][通常論文]
    ダウンロード
  • 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年03月 [査読無し][通常論文]
  • 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年03月 [査読無し][通常論文]
  • 松島 喜雄, 高倉 伸一, 畑 真紀, 宇津木 充, 橋本 武志, 上嶋 誠 日本火山学会講演予稿集 2017 46 -46 2017年
  • 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年
  • 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年
  • 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年
  • 橋本 武志, 田中 良, 上澤 真平, 山田 大志, 長谷川 健, 小園 誠史, 萬年 一剛, 中道 治久, 隅田 まり, 鈴木 由希, 田島 靖久, 高木 朗充 火山 62 (4) 189 -196 2017年 [査読有り][通常論文]
  • 畑 真紀, 高倉 伸一, 松島 喜雄, 橋本 武志, 宇津木 充 日本火山学会講演予稿集 2016 96 -96 2016年
  • 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年
  • 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年
  • 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年 [査読無し][通常論文]
  • 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年
  • 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年
  • 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年
  • 橋本 武志, 神田 径, 宇津木 充, 市來 雅啓, 小山 崇夫 日本火山学会講演予稿集 2015 (0) 186 -186 2015年 [査読無し][通常論文]
  • 橋本 武志, 三嶋 渉 日本火山学会講演予稿集 2014 55 -55 2014年11月02日
  • 山谷 祐介, 高橋 良, 岡崎 紀俊, 田村 慎, 岡 大輔, 秋田 藤夫, 茂木 透, 橋本 武志, 道下 剛史, 田中 良, 菅野 倖太朗, 奥田 真央 日本火山学会講演予稿集 2014 56 -56 2014年11月02日
  • 田中 良, 橋本 武志, 寺田 暁彦 日本火山学会講演予稿集 2014 125 -125 2014年11月02日
  • 三嶋渉, 橋本武志, 味喜大介, 大島弘光 日本火山学会講演予稿集 2014 148 -148 2014年 [査読無し][通常論文]
  • 青山裕, 森済, 橋本武志, 大島弘光, 村上亮 日本火山学会講演予稿集 2014 52 -52 2014年 [査読無し][通常論文]
  • 青山裕, 橋本武志, 森済, 大島弘光, 村上亮, 碓井勇二, 宮本聖史 日本火山学会講演予稿集 2013 33 -33 2013年 [査読無し][通常論文]
  • 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年09月11日 [査読無し][通常論文]
  • 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年03月 [査読無し][通常論文]
    ダウンロード
  • 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年
  • 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年 [査読無し][通常論文]
  • 相澤 広記, 吉村 令慧, 山崎 健一, 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 日本火山学会講演予稿集 2012 (0) 2012年 [査読無し][通常論文]
  • 神田 径, 宇津木 充, 小川 康雄, 高倉 伸一, 小山 崇夫, 橋本 武志, 小森 省吾, 園田 忠臣, 佐藤 泉, 井上 直人 日本火山学会講演予稿集 2012 (0) 2012年 [査読無し][通常論文]
  • 宇津木 充, 神田 径, 橋本 武志, 井上 直人, 小森 省吾, 井上 寛之, 井口 正人 日本火山学会講演予稿集 2012 (0) 2012年 [査読無し][通常論文]
  • 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年10月 [査読無し][通常論文]
  • 茂木 透, 山谷 祐介, 橋本 武志, 秋田 藤夫, 柴田 智郎, 高橋 徹哉, 田村 慎 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年09月13日
  • 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年09月13日 [査読無し][通常論文]
  • 岡崎 健治, 茂木 透, 宇津木 充, 山崎 貴志, 伊東 佳彦, 橋本 武志, 山谷 祐介, 伊藤 久敏, 海江田 秀志, 佃 十宏, 結城 洋一, 城森 明, 国島 英樹, 高橋 幸継 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年05月10日
  • 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年03月 [査読無し][通常論文]
    ダウンロード
  • 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年
  • 相澤 広記, 小山 崇夫, 長谷 英彰, 上嶋 誠, 橋本 武志, 宇津木 充, 吉村 令慧, 神田 径, 小川 康雄 日本火山学会講演予稿集 2011 (0) 23 -23 2011年 [査読無し][通常論文]
  • 橋本 武志, 中塚 正, 大熊 茂雄, 宇津木 充, 小山 崇夫, 神田 径 日本火山学会講演予稿集 2011 (0) 89 -89 2011年 [査読無し][通常論文]
  • 小山 崇夫, 橋本 武志, 八神 樹, 神田 径, 小川 康雄, 鍵山 恒臣, 宇津木 充, 吉村 令慧, 山崎 健一, 小松 信太郎, 上嶋 誠, 長谷 英彰, 相澤 広記, 山谷 祐介, 菅野 貴之, 渡邉 篤志, 宮川 幸治, 前原 祐樹 日本火山学会講演予稿集 2011 (0) 121 -121 2011年 [査読無し][通常論文]
  • 江尻 省, 中村 卓司, 鈴木 秀彦, 阿保 真, 橋本 武志, 寺田 暁彦 日本火山学会講演予稿集 2011 (0) 2011年 [査読無し][通常論文]
  • 池羽 健二, 阿保 真, 橋本 武志, 寺田 暁彦, 江尻 省, 中村 卓司 日本火山学会講演予稿集 2011 (0) 2011年 [査読無し][通常論文]
  • 繰り返し空中磁気測量で検出された有珠山の全磁力変化
    橋本武志, 宇津木充, 中塚 正, 大熊茂雄, 小山崇夫, 神田 径, 鈴木敦生 Conductivity Anomaly研究会論文集 29 -36 2011年 [査読無し][通常論文]
  • 橋本武志, 茂木 透, 清水淳平, 井 智史 Conductivity Anomaly研究会論文集 21 -28 2011年 [査読無し][通常論文]
  • 宮村淳一, 岡崎紀俊, 伏谷祐二, 重野伸昭, 橋本武志 北海道大学地球物理学研究報告 74 (74) 1 -19 2011年 [査読無し][通常論文]
     
    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年10月09日 [査読無し][通常論文]
  • 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年09月27日 [査読無し][通常論文]
  • 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年
  • 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年
  • 神田 径, タンク ブレント, カヤ チュライ, 小川 康雄, 笠谷 貴史, 八木原 寛, 市原 寛, 橋本 武志, 小山 崇夫, 宇津木 充, 井上 寛之, 園田 忠臣 日本火山学会講演予稿集 2010 (0) 2010年 [査読無し][通常論文]
  • 橋本武志, 茂木 透, 西村三治, 有田 真 Conductivity Anomaly研究会論文集 56 -63 2010年 [査読無し][通常論文]
  • 山谷祐介, 橋本武志, 茂木 透, 村上 亮, 岡崎紀俊, 吉本充弘, 伏谷祐二, 橋本雅樹, 山本輝明, 西村三治, 有田 真, 的場敦史, 土屋遼平 北海道大学地球物理学研究報告 73 (73) 281 -294 2010年 [査読無し][通常論文]
     
    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.
  • 橋本武志, 西村三治, 有田 真, 山本輝明, 小木曽仁, 重野伸昭, 岡崎紀俊, 茂木 透 北海道大学地球物理学研究報告 73 (73) 269 -280 2010年 [査読無し][通常論文]
     
    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.
  • 土屋 遼平, 青山 裕, 橋本 武志, 森 済, 大島 弘光, 鈴木 敦生, 的場 敦史, 尾崎 威 日本火山学会講演予稿集 2009 2009年10月10日 [査読無し][通常論文]
  • 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年
  • 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年
  • 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年
  • 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年
  • 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年 [査読有り][通常論文]
  • 中塚 正, 宇津木充, 大熊茂雄, 田中良和, 橋本武志 Conductivity Anomaly 研究会論文集 108 -114 2009年 [査読無し][通常論文]
  • 山谷祐介, 茂木 透, 長谷英彰, 山下晴之, 鈴木敦生, 橋本武志 Conductivity Anomaly 研究会論文集 23 -30 2009年 [査読無し][通常論文]
  • 米塚スコリア丘の内部構造
    橋本武志, 宇津木充, 小森省吾 第４回阿蘇火山の集中総合観測報告書 43 -55 2009年 [査読無し][通常論文]
  • 高倉伸一, 橋本武志, 小川康雄, 井上寛之, 山谷祐介, 市原 寛, 茂木 透, 宇津木充, 松島喜雄, 佐藤秀幸 北海道大学地球物理学研究報告 72 (72) 117 -124 2009年 [査読無し][通常論文]
     
    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.
  • 小池哲司, 長谷川浩, 藤井郁子, 橋本武志 北海道大学地球物理学研究報告 70 (72) 107 -115 2009年 [査読無し][通常論文]
     
    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.
  • 橋本武志, 小川康雄, 高倉伸一, 山谷祐介, 市原 寛, 宇津木充, 井上寛之, 小池哲司, 長谷川浩, 茂木 透 北海道大学地球物理学研究報告 72 (72) 79 -105 2009年 [査読無し][通常論文]
     
    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.
  • 寺田 暁彦, 吉川 慎, 橋本 武志, 鍵山 恒臣, 佐々木 寿 日本火山学会講演予稿集 2008 2008年10月10日 [査読無し][通常論文]
  • 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年03月 [査読無し][通常論文]
    ダウンロード
  • 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年
  • 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年
  • 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年 [査読無し][通常論文]
  • 神田 径, 橋本武志, Tony Hurst, 坂中伸也, 山田健太, 小川康雄, 相沢広記, 高倉伸一, 大久保綾子, 小山崇夫, 小林 宰, 田中良和, 宇津木充, 井上寛之, 小森省吾, 石原和弘, 山崎友也, 高山鉄朗, 為栗 健 Conductivity Anomaly 研究会論文集 131 -134 2008年 [査読無し][通常論文]
  • 寺田暁彦, 橋本武志 月刊地球号外 S60 (60) 121 -132 2008年 [査読無し][通常論文]
  • 山谷 祐介, 橋本 武志, 茂木 透 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年10月01日
  • 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年 
    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年
  • 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年
  • 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年
  • 浅間火山2005年空中磁気異常の1992年 データとの比較
    中塚 正, 宇津木充, 大熊茂雄, 田中良和, 浅間山電磁気構造探査グループ, 橋本武志 Conductivity Anomaly研究会論文集 120 -125 2007年 [査読無し][通常論文]
  • 有珠山西山火口群での全磁力測量
    小池哲司, 長谷川浩, 藤井郁子, 大和田毅, 徳本哲男, 大川隆志, 橋本武志 Conductivity Anomaly研究会論文集 130 -135 2007年 [査読無し][通常論文]
  • 青山 裕, 鬼澤真也, 為栗 健, 鈴木敦生, 前川徳光, 大島弘光, 森 済, 橋本武志, 志賀 透, 小山 寛, 中橋正樹, 吉川章文, 福山由朗 北海道大学地球物理学研究報告 70 (70) 107 -121 2007年 [査読無し][通常論文]
     
    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.
  • 長谷英彰, 橋本武志, 西田泰典, 宇津木充, 井上寛之, 佐波瑞恵 北海道大学地球物理学研究報告 70 (70) 43 -52 2007年 [査読無し][通常論文]
     
    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.
  • 西田泰典, 橋本武志 北海道大学地球物理学研究報告 70 (70) 1 -12 2007年 [査読無し][通常論文]
     
    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.
  • 橋本武志, 茂木 透, 西田泰典, 高田真秀, 鈴木敦生, 前川徳光, 佐藤秀幸 北海道大学地球物理学研究報告 70 (70) 123 -135 2007年 [査読無し][通常論文]
     
    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.
  • 寺田 暁彦, 佐々木 寿, 橋本 武志, 鍵山 恒臣, 齋藤 武士, 吉川 慎 日本火山学会講演予稿集 2006 2006年10月23日 [査読無し][通常論文]
  • 橋本武志, 池辺伸一郎 日本火山学会講演予稿集 2006 2006年
  • 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年
  • 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年
  • 及川 純, 鍵山 恒臣, 田中 聡, 宮町 宏樹, 筒井 智樹, 池田 靖, 潟山 弘明, 松尾 釧道, 大島 弘光, 西村 裕一, 山本 圭吾, 渡辺 俊樹, 山崎 文人, 渡辺 秀文, 藤井 敏嗣, 中田 節也, 武尾 実, 大湊 隆雄, 金子 隆之, 吉本 充宏, 竹田 豊太郎, 小山 悦郎, 長田 昇, 坂 守, 羽田 敏夫, 橋本 信一, 辻 浩, 井本 良子, 増谷 文雄, 嶋野 岳人, 古川 晃子, 鷺谷 威, 藤井 巌, 林 能成, 宮島 力男, 山田 守, 奥田 隆, 伊藤 武雄, 橋本 武志, 前川 徳光, 鈴木 敦生, 伊藤 拓, 三浦 康, 植木 貞人, 西村 太志, 仁田 交市, 佐藤 峰司, 下村 陽一, 野上 健治, 鬼澤 真也, 小山田 浩子, 舟崎 淳, 近澤 心, 藤原 健治, 濱田 信生, 青木 元, 高木 朗充, 山本 哲也, 林 豊, 金尾 政紀, 山下 幹也, 清水 洋, 渡邉 篤志, 是永 将宏, 大倉 敬宏, 吉川 慎, 池田 さや香, 井口 正人, 為栗 健, 八木原 寛, 平野 舟一郎 東京大学地震研究所彙報 81 (1) 71 -94 2006年 [査読無し][通常論文]
     
    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年 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • 長谷 英彰, 橋本 武志, 西田 泰典, 宇津木 充, 井上 寛之 日本火山学会講演予稿集 2006 (0) 2006年 [査読無し][通常論文]
  • 橋本 武志, 小池 哲司, 長谷川 浩, 藤井 郁子, 山谷 祐介, 市原 寛, 茂木 透, 小川 康雄, 宇津 木充, 井上 寛之, 高倉 伸一, 佐藤 秀幸 日本火山学会講演予稿集 2006 (0) 2006年 [査読無し][通常論文]
  • 齋藤武士, 大沢信二, 橋本武志, 寺田暁彦, 吉川慎, 大倉敬宏 日本火山学会講演予稿集 2006 54 2006年 [査読無し][通常論文]
  • 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, 相沢広記, 平林順一, 松尾元広, 野上健治, 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 Conductivity Anomaly 研究会論文集 78 -79 2006年 [査読無し][通常論文]
  • 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―
    橋本武志 Conductivity Anomaly 研究会論文集 51 -58 2006年 [査読無し][通常論文]
  • 火山岩のゼータ電位測定実験
    橋本武志, 長谷英彰, 佐藤佳子 平成16～17年度科学研究費補助金基盤研究(C)研究成果報告書（研究代表者：橋本武志） 8 -16 2006年 [査読無し][通常論文]
  • ホワイトアイランドにおける地上繰り返し磁気測量
    橋本武志, 神田 径, A.W.Hurst, 宇津木充, 吉村令慧, ホワイト島火山空中磁気測量チーム 平成15～17年度科学研究費補助金基盤研究(B)研究成果報告書（研究代表者：田中良和） 107 -140 2006年 [査読無し][通常論文]
  • ロングバレー・カルデラ －地殻活動の現在－
    橋本武志 月刊地球 28 (2) 132 -139 2006年 [査読無し][通常論文]
  • 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年03月 
    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年
  • 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年
  • 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年
  • 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年
  • 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年 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • 山谷祐介, 橋本武志, 茂木透, 鈴木敦生, 西田泰典, 谷元健剛, 森 済, 寺田暁彦, 三品正明, 長谷英彰 北海道大学地球物理学研究報告 68 (68) 127 -140 2005年 [査読無し][通常論文]
  • 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, 荻原 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, 斎藤 政城, 平野 舟一郎, 上釜 友大, 井口 元冶, 竹下 孝弘, 森 健彦 東京大学地震研究所彙報 80 (1) 11 -40 2005年 [査読無し][通常論文]
     
    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.
  • 橋本武志 火山 50 S115 -S138 2005年 [査読無し][通常論文]
     
    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.
  • ボーリングコアサンプル（高野尾羽根溶岩）のゼータ電位測定
    長谷英彰, 石戸経士, 橋本武志, 古川邦之 ＣＡ研究会論文集 48 -53 2005年 [査読無し][通常論文]
  • 長谷 英彰, 石戸 経士, 橋本 武志 Conductivity anomaly研究会論文集 25 -32 2004年
  • 橋本 武志, 茂木 透, 西田 泰典 Conductivity anomaly研究会論文集 46 -54 2004年
  • 山谷祐介, 茂木透, 橋本武志 日本火山学会講演予稿集 2004 2004年
  • 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年
  • 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年
  • 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年
  • 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年 [査読無し][通常論文]
  • 山谷祐介, 谷元健剛, 西田泰典, 佐波瑞恵, 宮原昌一, 吉田邦一, 茂木 透, 橋本武志 北海道大学地球物理学研究報告 67 39 -51 2004年 [査読無し][通常論文]
  • 橋本武志, 茂木 透, 西田泰典, 小川康雄, 平林順一, 及川光弘, 齋藤政城, 水橋正英, 氏原直人, ヌルハッサン, 若林 亨 第４回草津白根火山の集中総合観測 133 -142 2004年 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • 相澤 広記, 吉村 令慧, 山崎 健一, 神田 径, 大志万 直人, 橋本 武志, HURST Tony, 坂中 伸也, 古川 勇也, 小川 康雄, TANK S.Bulent, 上嶋 誠, 小河 勉, 小山 茂, 鍵山 恒臣, 塩崎 一郎, 宇都 智史, 吉村 光弘, 吉本 和範 京都大学防災研究所年報. B = Disaster Prevention Research Institute Annuals. B 46 (0) 729 -737 2003年04月01日 [査読無し][通常論文]
     
    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年 [査読無し][通常論文]
  • 橋本武志, 網田和宏, 長谷英彰, 田中良和 大分県温泉調査研究会報告 54 (54) 91 -96 2003年 [査読無し][通常論文]
  • 橋本武志, 田中良和, Malcolm J, S. Johnston, 宇津木充, 笹井洋一, 坂中伸也 京都大学防災研究所年報 46 (B) 765 -777 2003年 [査読無し][通常論文]
  • 笹井 洋一, 上嶋 誠, 歌田 久司, 鍵山 恒臣, ZLOTNICKI J, 橋本 武志, 高橋 優志 日本火山学会講演予稿集 2002 (2) 2002年10月22日 [査読無し][通常論文]
  • 杉岡 学, 鍵山 恒臣, 笹井 洋一, 上嶋 誠, 橋本 武志 日本火山学会講演予稿集 2002 (2) 2002年10月22日 [査読無し][通常論文]
  • 小河 勉, 鍵山 恒臣, 田中 良和, 橋本 武志, 長谷 英彰 日本火山学会講演予稿集 2002 (2) 2002年10月22日 [査読無し][通常論文]
  • 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年10月22日 [査読無し][通常論文]
  • 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年07月
  • 須藤 靖明, 筒井 智樹, 小野 博尉[他], 田中 良和, 橋本 武志, 外 輝明, 増田 秀晴, 迫 幹雄, 吉川 慎, 坂中 伸也, 森 健彦, 中坊 真, 長谷 英彰, 松下 誠司, 筒井 麻貴, 吉川 美由紀, 岡田 弘, 前川 徳光, 勝俣 啓, 和田 直人, 浜口 博之, 田中 聡, 仁田 交市, 堀 修一郎, 西村 大志, 田中 佐千子, 渡邊 理恵子, 小林 知勝, 大場 武 東京大學地震研究所彙報 77 (4) 303 -336 2002年 [査読無し][通常論文]
     
    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.
  • 電磁気探査から推定される阿蘇火山中央火口丘の浅部構造
    橋本武志, 田中良和, 網田和宏, 神田 径, 坂中伸也, 鍵山恒臣 平成9～12年度科学研究費補助金基盤研究(A)研究成果報告書（研究代表者：川勝均） 2002年 [査読無し][通常論文]
  • 中坊 真, 小野博尉, 迫 幹雄, 橋本武志, 須藤靖明, 大倉敬宏, 吉川 慎, 宇津木充, 坂中伸也, A. W. Hurst 京都大学防災研究所年報 45 (B) 633 -644 2002年 [査読無し][通常論文]
  • 長谷英彰, 高倉伸一, 石戸経士, 佐藤佳子, 橋本武志, 田中良和, 大倉敬宏 京都大学防災研究所年報 45 (B) 645 -656 2002年 [査読無し][通常論文]
  • 九重硫黄山の熱放出過程と地磁気変化
    橋本武志, 宇津木充, 坂中伸也, 田中良和 京都大学防災研究所年報 45 (B) 617 -625 2002年 [査読無し][通常論文]
  • 2001年鳥取県西部地震震源域周辺での深部比抵抗構造探査の概要
    年地殻比抵抗研究グループ 京都大学防災研究所年報 45 (B) 489 -497 2002年 [査読無し][通常論文]
  • 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年10月01日 [査読無し][通常論文]
  • 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年
  • 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年
  • 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年
  • 橋本武志, 田中良和, 宇津木充 京都大学防災研究所年報 44 (B-1) 333 -343 2001年 [査読無し][通常論文]
  • 坂中伸也, 田中良和, 宇津木充, 橋本武志 秋田大学工学資源学部研究報告 22 25 -38 2001年 [査読無し][通常論文]
     
    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.
  • 全磁力変化から推定される阿蘇中岳火口の熱放出過程と浅部構造
    橋本武志 京都大学防災研究所研究集会12K-3「火山の浅部構造と火山流体」論文集 149 -159 2001年 [査読無し][通常論文]
  • 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年
  • 阿蘇火山中央火口丘における自然電位観測
    長谷英彰, 田中良和, 橋本武志, 坂中伸也 京都大学防災研究所年報 43 (B-1) 47 -53 2000年 [査読無し][通常論文]
  • MT法による阿蘇カルデラの比抵抗断面
    高倉伸一, 橋本武志, 小池克明, 小川康雄 CA研究会論文集 23 -30 2000年 [査読無し][通常論文]
  • 注水試験時の電磁気観測(2)−流動電位計測−
    村上英記, 橋本武志, 大志万直人, 山口 覚 月刊地球総特集「野島断層注水実験と誘発地震」 23 250 -255 2000年 [査読無し][通常論文]
  • 中坊 真, 小野 博尉, 迫 幹雄, 橋本 武志, 須藤 靖明 日本地熱学会学術講演会講演要旨集 1999 1999年12月01日
  • 高倉 伸一, 橋本 武志, 小池 克明, 小川 康雄 日本地熱学会学術講演会講演要旨集 1999 1999年12月01日
  • 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年10月09日 [査読無し][通常論文]
  • 網田 和宏, 橋本 武志, 増田 秀晴, 森 健彦, 中坊 真, 山本 希, 川勝 均, 井出 哲, 金嶋 聡, 大湊 隆雄 日本地熱学会誌 21 (1) 76 -76 1999年01月25日
  • 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年
  • 神田 径, 茂木 透, 宗包 浩志, 小河 勉, 小野 博尉, 坂中 伸也, 下泉 政志, 田中 良和, Widarto D. S, 網田 和宏, 半田 駿, 長谷 英彰, 橋本 武志, 生駒 良友, 鍵山 恒臣, 小山 崇夫, 増田 秀晴 日本火山学会講演予稿集 1999 (0) 134 -134 1999年 [査読無し][通常論文]
  • 橋本 武志, 茂木 透, 宗包 浩志, 小河 勉, 小野 博尉, 坂中 伸也, 下泉 政志, 田中 良和, Djedi S. W, 網田 和宏, 半田 駿, 長谷 英彰, 生駒 良友, 鍵山 恒臣, 神田 径, 小山 崇夫, 増田 秀晴 日本火山学会講演予稿集 1999 (0) 1999年 [査読無し][通常論文]
  • 阿蘇火山構造探査における人工地震に伴う地電位変化
    長谷英彰, 田中良和, 橋本武志, 坂中伸也, 森 健彦, 増田秀晴, 吉川 慎 ＣＡ研究会論文集 193 -200 1999年 [査読無し][通常論文]
  • 神田 径, 橋本武志, 大島弘光 京都大学防災研究所年報. 42 (B-1) 11 -18 1999年 [査読無し][通常論文]
  • 阿蘇中央火口丘の自然電位(1)
    田中良和, 橋本武志, 長谷英彰, 坂中伸也, 増田秀晴 CA研究会論文集 187 -192 1999年 [査読無し][通常論文]
  • 橋本武志, 網田和宏, 馬渡秀夫, 田中良和 CA研究会論文集 (1999) 29 -37 1999年 [査読無し][通常論文]
  • 橋本武志, 田中良和, 茂木透, 西田泰典, 神田 径, 山本圭吾, 石原和弘, 平林順一 京都大学防災研究所年報 42 (B-1) 19 -25 1999年 [査読無し][通常論文]
  • 桜島火山における高密度電気探査
    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 京都大学防災研究所共同研究9P-5「桜島火山の地下水・熱水系に関する研究」報告書 103 -108 1999年 [査読無し][通常論文]
  • 諏訪之瀬島火山の自然電位・全磁力測定
    神田 径, 森 真陽, 橋本武志, 大島弘光 第3回諏訪之瀬島火山の集中総合観測報告 41 -53 1999年 [査読無し][通常論文]
  • 桜島火山の自然電位
    橋本武志, 田中良和, 西田泰典, 茂木 透, 山本圭吾, 平林順一, 石原和弘 京都大学防災研究所共同研究9P-5「桜島火山の地下水・熱水系に関する研究」報告書 65 -101 1999年 [査読無し][通常論文]
  • 中坊 真, 須藤 靖明, 筒井 智樹, 吉川 美由紀, ガルセス ミルトン, 田中 良和, 西島 潤, 米重 和馬, 川口 昌宏, 工藤 貴久, 藤光 康宏, 迫 幹雄, 吉川 慎, 増田 秀晴, 外 輝明, 橋本 武志, ディアゴ ファン カルロス, 長谷 英彰, 小野 博尉 日本火山学会講演予稿集 1998 (0) 64 -64 1998年 [査読有り][通常論文]
  • 吉川 慎, 森 健彦, 増田 秀晴, 迫 幹雄, 外 輝明, 橋本 武志, 筒井 智樹, 須藤 靖明 日本火山学会講演予稿集 1998 (0) 117 -117 1998年 [査読有り][通常論文]
  • 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年 [査読無し][通常論文]
  • 野島注水実験時の電磁気観測
    村上英記, 橋本武志, 大志万直人, 山口 覚, 本蔵義守, 住友則彦 ＣＡ研究会論文集 209 -216 1998年 [査読無し][通常論文]
  • 野島注水実験時の電磁気観測
    村上英記, 橋本武志, 大志万直人, 住友則彦, 山口 覚, 本蔵義守 月刊地球号外 S21 54 -58 1998年 [査読無し][通常論文]
  • 九州中部におけるネットワークＭＴ観測
    田中良和, 網田和宏, 大羽成征, 馬渡秀夫, 橋本武志, 下泉政志, 笹井洋一 ＣＡ研究会論文集 243 -253 1998年 [査読無し][通常論文]
  • ＭＴ法から推定される阿蘇カルデラの比抵抗構造（序報）
    高倉伸一, 橋本武志, 小川康雄, 西垣俊宏 ＣＡ研究会論文集 225 -232 1998年 [査読無し][通常論文]
  • 地電流ノイズを利用した野島断層周辺の比抵抗調査
    橋本武志 月刊地球号外 S21 82 -86 1998年 [査読無し][通常論文]
  • 橋本武志, 田中良和, 茂木 透, 西田泰典, 大羽成征, 山本圭吾, 石原和弘 京都大学防災研究所年報 41 (B-1) 145 -151 1998年 [査読無し][通常論文]
  • 桜島火山における自然電位測定(序報)
    橋本武志, 田中良和, 大羽成征, 西田泰典, 谷元健剛, 宇津木充, 茂木 透, 山本圭吾, 石原和弘, 山崎 明, 伊藤暢宏, 池亀孝光 第9回桜島火山の集中総合観測報告書 71 -78 1998年 [査読無し][通常論文]
  • 橋本 武志, 大志万 直人, 住友 則彦, 村上 英記, 山口 覚, 本蔵 義守 日本地震学会講演予稿集 = Programme and abstracts, the Seismological Society of Japan 1997 (2) 1997年09月15日
  • 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年
  • 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年
  • 火山噴火に伴う自然電位変動
    橋本武志 1997年CA研究会論文集 16 -20 1997年 [査読無し][通常論文]
  • 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年11月05日 [査読無し][通常論文]
  • 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年11月05日 [査読無し][通常論文]
  • 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年11月05日 [査読無し][通常論文]
  • 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年
  • 中坊 真, 由佐 悠紀, 北岡 豪一, 大沢 信二, 馬渡 秀夫, 大上 和敏, 森 健彦, 小林 芳正, 須藤 靖明, 筒井 智樹, 橋本 武志, 吉川 慎, 松本 良浩, 田中 麻貴 日本火山学会講演予稿集 1996 (0) 112 -112 1996年 [査読有り][通常論文]
  • 中坊 真, 大羽 成征, 田中 麻貴, 迫 幹雄, 外 輝明, 増田 秀晴, 山田 年広, 吉川 慎, 小林 芳正, 茂木 透, 橋本 武志, 須藤 靖明, 筒井 智樹, 小野 博尉, 田中 良和, 菊池 茂智, 森 健彦, 松本 良浩 日本火山学会講演予稿集 1996 (0) 173 -173 1996年 [査読有り][通常論文]
  • 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年 [査読無し][通常論文]
  • 熱水活動の指標としての自然電位−1990-1995年雲仙岳噴火におけるケーススタディ−
    橋本武志 1996年CA研究会論文集 222 -229 1996年 [査読無し][通常論文]
  • 自然電位法を用いた雲仙火山の地下熱水系に関する研究
    田中良和, 橋本武志, 鍵山恒臣, 歌田久司 東京大学地震研究所広報 12 7 -9 1996年 [査読無し][通常論文]
  • 九重硫黄山における電磁気観測
    田中良和, 茂木 透, 橋本武志, 増田秀晴, 行武 毅, 大羽成征 平成7年度科学研究費研究成果報告書 125 -140 1996年 [査読無し][通常論文]
  • 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年
  • 橋本武志, 田中良和 日本火山学会講演予稿集 1995 1995年
  • 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 日本火山学会講演予稿集 1995 (0) 96 -96 1995年 [査読有り][通常論文]
  • 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年 [査読無し][通常論文]
  • 霧島新燃岳火口湖の水上電位測定
    橋本武志, 本蔵義守, 大谷冬彦 1995年CA究会論文集 23 -30 1995年 [査読無し][通常論文]
  • 橋本武志, 大学合同観測班電磁気観測グループ 平成6年度科学研究費研究成果報告書 80 -86 1995年 [査読無し][通常論文]
  • 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年04月
  • 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年
  • 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年
  • 橋本武志, 田中良和 日本火山学会講演予稿集 1994 1994年
  • 電極問題についての一考察
    橋本武志 1994年CA研究会論文集 86 -97 1994年 [査読無し][通常論文]
  • 橋本武志, 田中良和, 須藤靖明 京都大学防災研究所年報 37 (B1) 183 -191 1994年 [査読無し][通常論文]
  • 雲仙岳火山活動と自然電位観測
    橋本武志, 大学合同観測班電磁気グループ 平成4-5年度科学研究費研究成果報告書 90 -102 1994年 [査読無し][通常論文]
  • 井上 智広, 元木 智広, 歌田 久司, 鍵山 恒臣, 増谷 文雄, 山口 勝, 橋本 武志 日本火山学会講演予稿集 1993 (2) 1993年10月04日 [査読無し][通常論文]
  • 橋本 武志, 田中 良和, 鍵山 恒臣, 増谷 文雄 日本火山学会講演予稿集 1993 (2) 1993年10月04日 [査読無し][通常論文]
  • 上嶋 誠, 歌田 久司, 鍵山 恒臣, 橋本 武志, 田中 良和, 雲仙火山MT観測グループ 日本火山学会講演予稿集 1993 (2) 1993年10月04日 [査読無し][通常論文]
  • 自然電位観測から推定される雲仙岳の地下熱水対流
    橋本武志, 田中良和, 増田秀晴, 歌田久司, 鍵山恒臣, 増谷文雄 1993年CA研究会論文集 249 -255 1993年 [査読無し][通常論文]
  • 橋本 武志, 田中 良和, 増田 秀晴, 歌田 久司, 鍵山 恒臣, 増谷 文雄 日本火山学会講演予稿集 1992 (2) 33 -33 1992年11月09日 [査読無し][通常論文]
  • 田中 良和, 橋本 武志, 増田 秀晴 日本火山学会講演予稿集 1992 85 -85 1992年
  • 三浦 敏郎, 小屋口 剛博, 田中 良和, 橋本 武志 日本火山学会講演予稿集 1992 82 -82 1992年
  • 1991年の雲仙岳における自然電位観測
    橋本武志, 田中良和, 増田秀晴, 歌田久司, 鍵山恒臣, 増谷文雄 CA研究会論文集 1992 249 -256 1992年 [査読無し][通常論文]
  • 鍵山 恒臣, 歌田 久司, 増谷 文雄, 山本 哲也, 村上 英記, 増田 秀晴, 橋本 武志, 田中 良和 日本火山学会講演予稿集 1991 (2) 152 -152 1991年10月14日 [査読無し][通常論文]
  • 田中 良和, 橋本 武志, 増田 秀晴, 半田 駿, 歌田 久司, 笹井 洋一 日本火山学会講演予稿集 1991 24 -24 1991年

書籍等出版物

  • Volcanic Lakes
    Hurst T, Hashimoto T, Terada A (担当:分担執筆範囲:Crater Lake Energy and Mass Balance)
    Springer 2015年
  • 日本地方地質誌1 北海道地方
    西田泰典, 橋本武志 (担当:分担執筆範囲:10.5 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年11月
  • 太陽地球系科学
    橋本武志 (担当:共著範囲:第10章 地球の磁場)
    京都大学学術出版会 2010年05月

講演・口頭発表等

  • Repeated aeromagnetic survey aiming for monitoring the volcanomagnetic effects and 3D imaging of the magnetization changes  [通常講演]
    Hashimoto T, K Shibuya
    IAVCEI 2023年01月 ポスター発表
  • 有珠⼭頂⽕⼝原の⻑期的冷却帯磁  [通常講演]
    橋本武志
    日本火山学会 2022年10月 ポスター発表
  • 十勝岳の火山活発化指数（VUI）基準の試作  [通常講演]
    橋本武志, 青山 裕, 田中 良, 大倉敬宏, 森 俊哉
    日本火山学会 2020年10月 口頭発表（一般）
  • From monitoring to forecasting -Toward statistical evaluation of non-magmatic unrest-  [招待講演]
    橋本武志
    International Workshop on the mechanism of Phreatic Eruption 2020年01月 口頭発表（招待・特別）
  • 噴気画像の自動処理  [通常講演]
    日本火山学会秋季大会 2019年09月 ポスター発表
  • Source characteristics of demagnetization and ground deformation during inter-eruptive periods  [通常講演]
    Hashimoto T, Utsugi M, Ohkura T, Kanda W, Terada A, Miura S, Iguchi M
    International Union of Geodesy and Geophysics 2019年07月 口頭発表（一般）
  • Simple and Fast Method to Remove Volcanic Smoke in Visible and TIR Imagery  [通常講演]
    Hashimoto T, Terada A, Tanaka R
    International Union of Geodesy and Geophysics 2019年07月 口頭発表（一般）
  • 火山ガス観測における無人機の利用  [通常講演]
    橋本武志, 寺田暁彦, 森 俊哉, 田中 良
    日本地球惑星科学連合 2019年05月 口頭発表（一般）
  • 非噴火期の地盤膨張源および消磁源の特徴について  [通常講演]
    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 2018年05月 口頭発表（一般）
  • 非噴火時における多項目観測の重要性（樽前山の事例）  [通常講演]
    橋本武志, 松本征海, 青山 裕, 小山 寛, 森井敦司, 三嶋 渉, 荻野 激, 高橋 良, 岡崎紀俊
    日本火山学会 2017年09月 口頭発表（一般）
  • Long-term Correlation between Geomagnetic Filed Changes, Ground Deformation and Gas Composition at Mt. Tarumae Volcano, Northern Japan  [通常講演]
    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年08月 口頭発表（一般）
  • 地盤変動と相関の高い火山性磁場変動  [通常講演]
    橋本武志, 田中 良
    日本火山学会 2016年10月 ポスター発表
  • Detection of Aeromagnetic Field Changes Using an Unmanned Autonomous Helicopter: Repeated Experiments at Tarumae Volcano (Japan)  [通常講演]
    Hashimoto T, Koyama T, Yanagisawa T, Yoshimoto M, Ohminato T, Kaneko T
    American Geophysical Union 2015年12月 ポスター発表
  • 噴気を除去する画像処理  [通常講演]
    橋本武志, 寺田暁彦, 田中 良
    日本火山学会 2015年09月 口頭発表（一般）
  • 熱水系卓越型火山の非噴火時に見られる地磁気変化の特徴  [通常講演]
    橋本武志, 神田 径, 宇津木充, 市來雅啓, 小山崇夫
    日本火山学会 2015年09月 ポスター発表
  • Long-term volcano-magnetic effects associated with phreatic eruptions  [通常講演]
    Hashimoto, T, Kanda, W, Utsugi, M, Ichiki, M
    International Union of Geodesy and Geophysics, General Assembly 2015年06月 口頭発表（一般）
  • 有珠山2000年噴火初期に観測された地磁気変化の再検討  [通常講演]
    橋本武志, 三嶋 渉
    日本火山学会 2014年11月 口頭発表（一般）
  • Geomagnetic Changes over Tarumae Volcano (Japan) Through Repeated Surveys Using an Unmanned Helicopter  [通常講演]
    Hashimoto T, Koyama T, Yanagisawa T, Yoshimoto M, Kaneko T, Ohminato T, Suzuki E
    Asia Oceania Geosciences Society 2014年07月 口頭発表（一般）
  • A low-cost SO2 imager with the use of digital cameras of consumer use  [通常講演]
    Hashimoto T, Terada A, Ejiri M, Nakamura T, Makoto Abo M
    International Association of Volcanology and Chemistry of Earth's Interior 2013年07月 ポスター発表
  • 無人ヘリコプターを利用した樽前火山の空中調査  [通常講演]
    橋本武志, 大湊隆雄, 金子隆之, 吉本充宏, 柳澤孝寿, 鈴木英一, 小山崇夫, 松本征海
    日本地球惑星科学連合 2013年05月 口頭発表（一般）
  • 道東地域の地磁気永年変化  [通常講演]
    橋本武志, 茂木透, 西村三治, 有田真, 清水淳平, 井智史, 源泰拓, 長町信吾
    日本地球惑星科学連合 2012年05月 口頭発表（一般）
  • 無人ヘリコプターを利用した樽前山の空中磁気測量  [通常講演]
    橋本武志, 小山崇夫, 金子隆之, 大湊隆雄, 吉本充宏, 鈴木英一, 柳澤孝寿
    日本地球惑星科学連合 2012年05月 口頭発表（一般）
  • 道東地域の地磁気全磁力永年変動について, ―IGRFによる広域変動場の評価―  [通常講演]
    橋本武志, 茂木 透
    地球電磁気・地球惑星圏学会 2011年11月 口頭発表（一般）
  • 民生デジタルカメラを利用した簡易SO2カメラの製作  [通常講演]
    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年10月 ポスター発表
  • 有珠山の空中磁気測量から推定される噴火後の冷却過程  [通常講演]
    橋本武志, 中塚正, 大熊茂雄, 宇津木充, 小山崇夫, 神田径
    日本火山学会 2011年10月 口頭発表（一般）
  • 繰り返し空中磁気測量で検出された有珠山の全磁力変化  [通常講演]
    橋本武志, 宇津木充, 中塚正, 大熊茂雄, 小山崇夫, 神田径, 鈴木敦生, 有珠山空中磁気探査グループ
    日本地球惑星科学連合 2011年05月 ポスター発表
  • 十勝岳の全磁力変化と蓄熱過程（その２）  [通常講演]
    橋本武志, 高橋裕二, 森井敦司, 清水淳平, 井智史, 岡崎紀俊, 宮村淳一, 十勝岳電磁気観測チー ム
    地球電磁気・地球惑星圏学会 2010年10月 口頭発表（一般）
  • 有珠山頂域の全磁力変化  [通常講演]
    橋本武志, 鈴木敦生, 松本征海
    日本火山学会 2010年10月 口頭発表（一般）
  • 有珠火山の空中磁気探査計画－地上観測から期待される磁場変化－  [通常講演]
    橋本武志, 宇津木充, 大熊茂雄, 中塚 正
    日本地球惑星科学連合 2010年05月 口頭発表（一般）
  • 十勝岳の全磁力変化と蓄熱過程 (2008-2009)  [通常講演]
    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 2009年10月
  • 十勝岳の全磁力変化と蓄熱過程 (2008-2009)  [通常講演]
    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
    地球電磁気・地球惑星圏学会 2009年09月 口頭発表（一般）
  • 阿蘇米塚スコリア丘の内部構造と形成過程  [通常講演]
    橋本武志, 宇津木充, 小森省吾
    日本地球惑星科学連合 2009年05月 口頭発表（一般）
  • Electric and magnetic changes associated with volcanic processes  [通常講演]
    Hashimoto T
    ASIAN INTERNATIONAL SYMPOSIUM ON MODELING OF VOLCANIC ERUPTION FOR VOLCANIC HAZARD ASSESSMENT 2008年12月 口頭発表（一般）
  • Resistivity structure across the intrusive zone of the 2000 eruption at Usu volcano  [通常講演]
    Hashimoto, T, Y. Ogawa, S. Takakura, Y. Yamaya, H. Ichihara, T. Mogi
    The 19th International Workshop on EM Induction of the Earth 2008年10月
  • 有珠山2000年新山域の比抵抗構造と貫入マグマ  [通常講演]
    橋本武志, 小川康雄, 高倉伸一, 山谷祐介, 市原 寛, 茂木 透
    日本地球惑星科学連合 2008年05月 口頭発表（一般）
  • Year-to-year Change in Self-potential on Unzen Volcano  [通常講演]
    Hashimoto, T, Year-to-year Change in Self-potential on, Unzen Volcano
    Cities on Volcano 5 2007年11月 ポスター発表
  • 有珠山で継続する全磁力変化  [通常講演]
    橋本武志, 鈴木敦生, 茂木 透, 山谷祐介
    地球電磁気・地球惑星圏学会 2007年09月 口頭発表（一般）
  • Imaging of the electrical and thermal structure of a shallow magmatic intrusion associated with the 2000 eruption of Usu Volcano  [通常講演]
    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年07月
  • 有珠山2000年新山域の地磁気変化  [通常講演]
    橋本武志, 鈴木敦生, 前川徳光, 茂木 透, 山谷祐介
    日本地球惑星科学連合 2007年05月 ポスター発表
  • 阿蘇中岳火口湯溜まりの水収支・熱収支再考(1991-2000)  [通常講演]
    橋本武志, 池辺伸一郎
    日本火山学会 2006年10月 口頭発表（一般） 阿蘇，熊本
    ダウンロード
  • 浅間火山のＭＴ法比抵抗構造探査 －山頂域西部・北東南西測線の解析－  [通常講演]
    橋本武志, 浅間山電磁気構造探査グループ
    日本地球惑星科学連合 2006年05月 ポスター発表 幕張
    ダウンロード
  • 平成17年度浅間山電磁気構造探査の概要  [通常講演]
    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年03月 東京
  • Helicopter-borne magnetic survey over White Island -Is volcanomagnetic effect detectable by repeated survey?-  [通常講演]
    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年01月 口頭発表（一般） 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－  [通常講演]
    橋本武志
    Conductivity Anomaly研究会 2005年12月 口頭発表（一般） 東京
  • Ｈ１７年度浅間山電磁気構造探査序報  [通常講演]
    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年12月 口頭発表（一般） 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年11月 口頭発表（一般） 東京
  • ドーム状隆起に伴う磁場変化－有珠山2000年噴火時の全磁力変化再検討－  [通常講演]
    橋本武志
    地球電磁気・地球惑星圏学会 2005年09月 京都市
  • 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－  [通常講演]
    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年07月 口頭発表（一般） 熊本
  • A helicopter-borne geomagnetic survey on White Island, New Zealand (FY2004)  [通常講演]
    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年05月 ポスター発表 千葉市幕張
    ダウンロード
  • 自然電位の定量的評価に向けた流動電位実験  [通常講演]
    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年03月 口頭発表（一般） 東京
  • On the annual variations in geomagnetic differences observed in Long Valley Caldera, California  [通常講演]
    Hashimoto, T, M. J, S. Johnston, Y. Tanaka, Y. Sasai, M. Utsugi, S. Sakanaka
    Inernational Union of Geodesy and Geophysics 2003年06月 口頭発表（一般） 札幌市
  • Heat discharge, water level and geomagnetic changes of the crater lake, Aso Volcano, Japan  [通常講演]
    Hashimoto, T, S. Ikebe, H. Ono, Y. Tanaka
    Western Pacific Geophysics Meeting 2002年07月 ウエリントン, ニュージーランド
    ダウンロード
  • マグマ貫入に伴う熱水対流系の発達と自然電位変動  [通常講演]
    橋本武志, 田中良和, 鍵山恒臣
    地球惑星科学関連学会 2002年05月 口頭発表（一般） 東京
    ダウンロード
  • 九重火山の熱放出過程と地磁気変化  [通常講演]
    橋本武志, 宇津木充, 坂中伸也, 田中良和
    京都大学防災研究所研究発表講演会 2002年02月 口頭発表（一般） 京都市
    ダウンロード
  • Self-potential changes on Unzen Volcano 1991-2001  [通常講演]
    Hashimoto, T, Y. Tanaka, T. Kagiyama
    雲仙国際ワークショップ 2002 2002年01月 ポスター発表 島原市
    ダウンロード
  • 阿蘇中岳火口における放熱量・水位および地磁気変化  [通常講演]
    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 2001年11月 福岡
    ダウンロード
  • 阿蘇火山中岳火口湯だまりの水位変動と放熱量について  [通常講演]
    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2001年秋季大会 2001年10月 口頭発表（一般） 鹿児島
    ダウンロード

担当経験のある科目（授業）

  • 構造探査学特論北海道大学大学院理学院自然史科学専攻
  • 地震火山計測特論北海道大学大学院理学院自然史科学専攻
  • 地球計測実習北海道大学理学部
  • 科学・技術の世界（地球惑星科学のフロンティア）北海道大学全学教育
  • 物理数学3北海道大学理学部
  • 地球惑星電磁気学北海道大学理学部
  • 地球惑星科学のための電磁気学北海道大学理学部

所属学協会

  • 国際火山学及び地球内部化学協会   日本地球惑星科学連合   日本火山学会   地球電磁気･地球惑星圏学会   

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2018年10月 -2019年03月 
    代表者 : 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
     
    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。大きな人的被害を出した厚真町の同時多発斜面崩壊では、周辺火山の噴火により厚く堆積した火砕降下物の底面に粘土化したすべり面が確認された。震源近くでは距離減衰式より大きな速度加速度が観測され、むかわ町の建物被害は地盤構造による地震動の増幅が影響しいる可能性が示された。札幌市内の住宅地で発生した液状化は、密度の小さな火山灰での谷埋め盛土と高い地下水位が関与している可能性が示された。道内全域停電が社会インフラや社会経済活動に与えた実態が明らかにされた。住民も対象とした成果報告会を開催し研究成果の社会還元を行った。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2014年10月 -2016年03月 
    代表者 : 山岡 耕春, 中田 節也, 三宅 康幸, 鈴木 毅彦, 山中 佳子, 大倉 敬宏, 松島 健, 中道 治久, 小澤 拓, 武尾 実, 橋本 武志, 森 俊哉, 寺田 暁彦, 野上 健治, 佐野 有司, 田所 敬一, 高木 朗充
     
    御嶽山の2014年噴火に関連した以下の成果を得た。（１）山頂周辺の地形変化と噴出物調査として、噴火前・後の航空写真、レーザ測量データ、人工衛星写真を取得し、噴火前後の映像を比較した。また山頂の現地調査を行い、噴火推移の詳細を明らかにした。（２）噴火前から取得されている各種データの解析、噴火後の地震計・傾斜計の設置と水準測量を実施し、水蒸気噴火に至るプロセスとその後の推移を明らかにした。（３）自立飛行無人機による火山ガス測定を行い、2014年噴火が1979年噴火と同じ経過をたどっていることを明らかにした。（４）火山災害情報の発信のあり方の調査を行い、御嶽山周辺住民の火山防災意識が明らかにした。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2012年04月 -2015年03月 
    代表者 : 橋本 武志, 寺田 暁彦, 森 俊哉, 中村 卓司, 江尻 省, 阿保 真
     
    これまで，火山噴気に含まれるH2O（水蒸気と水滴）を遠隔測定で定量することは一般に困難であるとされてきた．本研究では，H2Oが赤外線を吸収することを利用して，噴気を通過してきた背景光の強度分布から，噴気中のH2Oを濃度分布として可視化することを目指してきた．本研究での検討の結果，この方法は，少なくとも我が国の多湿な大気環境ではうまくいかないことが明らかになったが，本課題の副産物として，紫外線分光でSO2を可視化する装置の改良ができた．また，軽量可搬型のラマンライダーによって噴気中の水蒸気と水滴を独立に定量することが可能になった．
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2009年 -2012年 
    代表者 : 神田 径, 橋本 武志, 八木原 寛, 笠谷 貴史, 小川 康雄, 小山 崇夫, 宇津木 充, 市原 寛
     
    姶良カルデラ直下に想定されるマグマ溜りおよび桜島火山へのマグマ供給経路に相当する電気比抵抗の構造を明らかにするために、主としてカルデラを西北西-東南東に横断する2測線に沿って電磁気観測を行った。2009年からの4年間で、海域16点を含む全44点でデータを取得した。2次元および3次元解析の結果、鹿児島地溝に沿って下部地殻から続く低比抵抗の領域がカルデラ中央から東部にかけて見つかり、マグマ供給系に関連した地下構造であると推測された。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2010年 -2011年 
    代表者 : 中田 節也, 清水 洋, 宮町 宏樹, 中道 治久, 大久保 修平, 森田 裕一, 石原 和弘, 中尾 茂, 大倉 敬宏, 植木 貞人, 大島 弘光, 上嶋 誠, 鍵山 恒臣, 神田 径, 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
     
    霧島山新燃岳では2011年1月末に300年ぶりのマグマ噴火が発生した。すなわち,11月26,27日に準プリニー式が起こり,引き続いて山頂火口に溶岩蓄積が4日間続いた。2～4月にはブルカノ式噴火が断続的に発生し,6月からは複数回の水蒸気噴火が起こった。2011 年9月中旬以降噴火は起きていない。この一連のマグマ噴火に先行して水蒸気爆発が繰り返し発生し,火山周辺地域の地震活動が活発化した。さらに,噴火の約1 年前からは,火口の北西約6kmの地下にあるマグマ溜まりの膨張を示す,顕著な地殻変動が観察された。また,地殻変動観察では,準プリニー式噴火や火口への溶岩蓄積に対応したマグマ溜まりの収縮が認められた。準プリニー式噴火に数10分先行して微弱な増圧が伴ったことが歪計解析から明らかになった。ブルカノ式噴火中の火山性微動の発生域は,火口直下からマグマ溜まりまでの間で起こっており,マグマ溜まりから火口へのマグマ移動に対応したと考えられる。ブルカノ式噴火にマグマ溜まりからマグマが移動することが重力的にも確認された。また,この噴火の直前には火口浅部の膨張,火山性地震が増加し,それと連動して火山ガス放出率が減少することが観測され,火道最上部におけるガス閉塞が噴火に先行したことが明らかになった。初期の噴出物には組成の2種類の異なる組成のマグマが認められ,噴火に先行してマグマ混合起こったことが明らかになった。今回の噴火で噴出したマグマの総量は約2500万m^3に達したと見積もられ,300年前の噴火の噴出量の3分の1程度であった。 噴火中には,300年前の噴火や国内外の類似火山の噴火例を参考に,噴火の推移を表す噴火シナリオの作成が試みられた。今回の噴火では顕著な土石流の発生がなかったが,噴出物が主に軽石であったため,顕著な雨浸透性悪化が起こらなかったためと考えられる。2011年1月末の噴火直後から再開したマグマ溜まりへのマグマ蓄積は,2011年末まで継続し,その膨張量は2011年1月噴火前とほぼ同様になった。その後,2012 年に入って山体膨張はほぼ停滞し,火口へのマグマ供給が停止したものと考えられる。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2009年 -2011年 
    代表者 : 橋本 武志, 中村 卓司, 寺田 暁彦, 阿保 真, 中村 卓司
     
    本課題は,大気科学の分野で多用される分光技術を火山研究に応用し,火山ガスのリモートセンシングに新展開を与えようとしたものである.研究期間内の主な成果は,(1)噴気中の水蒸気分布を測定する可搬型ラマンライダーを改良し,水滴も測定可能としたこと,(2)噴気内部の温度分布測定を可能にする高スペクトル分解能ライダーを新規開発したこと,(3)一般用のデジタルカメラを利用して,二酸化硫黄濃度分布を可視化する簡易型の「SO2カメラ」を製作したこと,の3点である.
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2006年 -2008年 
    代表者 : 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.
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2005年 -2008年 
    代表者 : 中川 光弘, 笠原 稔, 橋本 武志, 高橋 浩晃, 西村 裕一, 吉本 充宏, 風早 康平, 石塚 吉浩, 金子 隆之, 金子 隆之, 風早 康平, 石塚 吉浩, 石川 剛志, 大場 武
     
    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。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2003年 -2006年 
    代表者 : 川勝 均, 須藤 靖明, 大倉 敬宏, 金嶋 聰, 山本 希, 橋本 武志, 及川 純
     
    本研究では,火山の噴火に伴うマグマ・ガズ・水などのものの流れを主に地震学的にとらえることで,阿蘇火山の噴火の準備過程,噴火過程,終息過程における物質の移動を定量化し,噴火のダイナミクスの理解を深めること,さらに阿蘇火山における将来の定量的火山噴火予測への道しるべとすることを目標としている.すでに判明している火山活動静穏期にみられる火山構造とその活動機構が,火山活動期にどのような変動を示すかを把握することを目指し,具体的には次のような目標を掲げた:(1)マグマ溜まりの変動把握(マグマ溜まりへのマグマの蓄積過程,あるいはマグマ溜まりから火口へ移動の検出)および定量化,(2)火道を通過するマグマ流動(上昇)・噴火時における高速ガス・土砂流等の検知および定量化,(3)長周期微動源(圧力源)の変動のリアルタイム・モニタリングによる地表表面(噴火)活動の予測. 上記の目標を達成するために,(1)中央火口丘周辺の10カ所でGPSによる連続観測をおこない,国土地理院の3観測点を含む計14点でマグマだまりの圧力変動をモニターした.(2)ガスの流れ等のモニターのため,短周期地震計アレイ観測を頻繁におこなった.(3)広帯域観測網をテレメータ化し,長周期微動源のリアルタイムモニターを開始した. 幸か不幸か,研究期間中に阿蘇山が活動期に入らなかったため,噴火に至る過程は観測できなかったものの,(1)アレイによる火山流体の高速移動の観測と発達した浅部火道システム存在の実証,(2)長周期微動(卓越周期15秒)と孤立型の短周期微動の関連を明らかにし,阿蘇火口直下の熱水系と一連の火山性微動を統一的に説明するモデルを構築,(3)境界積分法に基づく火山性微動解析の普遍的ツールの開発等,数多くの成果が得られた. 今後は,構築された観測網を維持し,阿蘇火山の活動期をとらえ当初の目標体制を継続的に目指す.
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2004年 -2005年 
    代表者 : 橋本 武志
     
    いくつかの火山で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.昨年度測定した資料について,表面伝導の効果を評価してゼータ電位を再計算した.岩石サンプル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が,このとき,サンプルの空隙ではなく,セルの表面による電気伝導の効果が無視できないことがわかったためである.また,昨年度未完成であった,圧力測定も行えるように部分的に装置を改良した. 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.今回再評価した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,造岩鉱物組成や,流動させる溶液側に溶解した成分まで考慮した検討が必要である. また,今年度は野外観測として,山頂部に自然電位異常の存在が知られている樽前山で比抵抗探査を実施したところ,山頂域の直下に極めて比抵抗の小さい領域が存在することが明らかになった.これは,山頂域の自然電位異常が地下の熱水対流系の流動電位によって生じている可能性を強くサポートするもので,流動数値計算によって自然電位の定量的解釈を行う上で不可欠な情報が得られたことになる.
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2003年 -2005年 
    代表者 : 田中 良和, 橋本 武志, 宇津木 充, 神田 径, 鍵山 恒臣, 大倉 敬宏, 松島 健
     
    平成15年度には,ニュージーランド国ホワイトアイランドに4名が渡航して、2地点にプロトン磁力計を設置して地上連続磁場観測を可能とした。また、自然電位分布観測を行った。16年度には5名が渡航して、連続磁場データの回収、地上繰り返し磁場観測を行うとともに、対地高度50mと100mの空中磁気測量を実施した。平成17年度には7名が渡航して地上および空中での繰り返し磁気測量を実施した。ホワイト島の火山活動は静穏で顕著な磁場変化は検出されなかった。しかし、この研究を通して空中磁気測量に関する観測技術的問題はほぼ解決された。即ち、飛翔体の位置決定は、高精度のGPS受信機を地上とバードに設置して、ディファレンシャル解析することで1m以下の誤差で求められること、機体へりの磁化の影響を避けるには40m離す必要があり、バード吊り下げ方式が優れること、安定な飛行を得るためのバードの形や円筒翼が決定できたこと、高精度のセシウム磁力計が大学で所有できたこと、パソコン画面に即時的にGPS位置を表示して航路誘導に用いるシステムが開発できた。この研究を契機として阿蘇、九重、桜島、磐梯、浅間の火山において飛行実験を積み重ねることが出来、空中磁気測量が大学の研究者によっても比較的簡単に実施可能であることを示せたことも成果の一つである。とりわけ、この研究の大きな目標であった空中磁気測量で火山性磁場変化を捉える課題は、九重火山における1996年と2004年の空中磁気測量データの解析から地上観測と整合的な50nTの火山性磁場変化を検出する成果を得たことで達成できたものと考えている。これらの研究成果は平成18年1月に筑波において開催されたISAG2006空中物理探査国際シンポジウムの研究会で発表を行った。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2003年 -2004年 
    代表者 : 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
    研究期間 : 2001年 -2002年 
    代表者 : 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.
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 1999年 -2001年 
    代表者 : 田中 良和, 下泉 政志, 橋本 武志
     
    九州陸域の地磁気誘導ベクトルが南西方向を指すこは,太平洋の誘導電流では説明できず,九州西方海域下の地殻電気伝導度は高いことが指摘されてきた.しかし,この海域での直接的な電場観測は殆どなされていない.近年,NTTのメタリック同軸ケーブルが営業品目から除外され,これを活用して下記の5地域で海底地電位を観測して電気構造を得ることが出来た. 地電位は横河電機7561,またはHP34970A+HP34902A電位計で増幅され,GPS時計に同期した1秒値がパソコンに収録された.MT解析に必要な磁場は鹿屋地磁気観測所を用いた. 1)沖縄地域:電場測線が東西であり,磁場のNS成分との相関は非常に高い.100-1000オームmの比抵抗が求まり,横方向にも均質である.30km深さまでが1000オームとの結果は島川の観測結果を支持するが,深いところで低抵抗である結果は得られていない. 2)鹿児島地域:電場と磁場の相関は東西にも南北にも良い.比抵抗として100-1000オームmが得られた.また,深部でも低抵抗にはならない. 3)甑島海域:甑島海域では数10オームmの比抵抗が求められた.これらは沖縄や鹿児島地域に比べて極めて低い.かつ,東西と南北での非一様性が特徴である. 4)長崎地域:下部地殻から上部マントルにかけての良導体の存在が特徴的である.30km深さまでは30オームm,80km深さまでは300オームm,それ以深で3オームmである. 5)壱岐地域:ここでも西部長崎地域と類似の良導体の存在が求められた.1kmより浅い部分で0.3オームm,1kmより深い部分で30オームmが得られた.
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 1999年 -2000年 
    代表者 : 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.
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 1997年 -2000年 
    代表者 : 川勝 均, 筒井 智樹, 金嶋 聰, 須藤 靖明, 大湊 隆雄, 橋本 武志
     
    本研究では,基本周期15秒という特異ともいえる阿蘇火山の長周期微動源の物理的実体と噴火活動における役割の解明を目指してきた.研究期間中に阿蘇山の噴火活動がなかったため後者の目標を達成することは出来なかったが,静穏期の観測研究から阿蘇山の火口直下の構造と火山性微動の発生様式の理解が進み多くの成果を得ることが出来た. 研究は火山における広帯域地震観測を一つのキーワードにし,複数の短周期アレイ観測,電磁気探査など様々な観測を行うと共に,噴火が起きた場合に備えての準備観測を平行して行った.成果を列挙すると,(1)稠密広帯域地震観測から微動の振動源の幾何学的形状(亀裂状の構造)を明らかにした.活動的火山の火口直下にこのような構造が地震学的に明らかにされたのは初めてのことである.(2)電磁気探査のデータ解析から,火口直下1kmあたりに低比抵抗層の存在を明らかにした.長周期微動の振動源を帯水層における熱水活動とした当初の予想と調和的な結果である.阿蘇火山では定常的な噴気活動が行なわれていることも考えると,これらの結果から,火口直下1km辺りに存在する帯水層において地下水/高温ガス/マグマなどの接触などによる熱水反応によって長周期振動が生み出されそれに伴って帯水層周辺に存在する亀裂群(亀裂・弱面の集合体)が開閉および膨張・収縮を繰り返しているという鮮明なイメージが浮かび上がってきた.(3)1994年に得られたデータの最解析をし,水蒸気爆発時にはその直前に長周期振動源が膨らみ,水蒸気爆発の準備段階が広帯域地震計で観測可能であることを示した.(4)短周期地震計アレイデータの解析から,短周期微動が長周期微動の励起源であることや,亀裂状構造から地表の噴気孔への流体の流れが明らかになりつつある.これらの成果は5編の英文論文として公表されている.
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 1997年 -1999年 
    代表者 : 西田 泰典, 鍵山 恒臣, 田中 良和, 笹井 洋一, 小川 康雄, 橋本 武志, 松波 武雄
     
    本研究目的:地球電磁気学的手法を用い,デイサイト質,玄武岩質,安山岩質の代表的火山として各々有珠山,三宅島,北海道駒ヶ岳を対象とし,1)火山水理学的構造探査,2)熱水対流系の分布形態解明,3)地下のマグマ探査,を行う. 1)火山水理学的構造推定には,マグネトテルリック法による比抵抗探査結果を指標とした.岩石種の違いにかかわらず,いずれの火山においても大局的には共通した特徴が見られた.すなわち,表層約100mは,火山岩や火山堆積物の影響で1000ohm-m程度の高比抵抗が存在し,十分な地下水の胚胎が見られない.それより深い第2層目は数-数10ohm-mの極めて低比抵抗層で特徴づけられる.この層はイオンを含んだ地下水や変質鉱物の存在により,低比抵抗になっている.第3層目は先第3系の高比抵抗の基盤岩(数100ohm-m)で構成され,水環境に乏しい. 2)いずれの火山にも,山頂火口原を中心に震幅の大きな正の自然電位異常が観測される(有珠山,400mV;三宅島,800mV;北海道駒ヶ岳,600mV).火山の自然電位異常の原因は地下水流動に伴う界面導電現象で解釈され,流れの下流部に正の異常が期待される.このことから,いずれの火山においても,地下に浸透した雨水が高温マグマまたは高温ガスによって温められ,再び中央火口原に上昇して正の異常を作ったと解釈される.このような大規模熱水対流系の存在が明らかになったことの異議は大きく,マグマの冷却過程を考える上で重要である. 3)マグネトテルリック観測から,有珠山火ロ原直下に約400ohm-mの相対的高比抵抗岩体の存在が明らかになった.室内岩石実験の結果(温度と比抵抗の関係)と現在の噴気温度(500〜600℃)とあわせて考えると,この比抵抗値はやく500℃のデイサイト質マグマの比抵抗値に対応するため,この岩体は1977-1978年噴火時の残存マグマと同定される.
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 1997年 -1998年 
    代表者 : 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
    研究期間 : 1995年
  • Self-potential and hydrothermal circulation in volcanic and geothermal areas Studies on subsurface structure of volcanoes using electromagnetic methods

Copyright © MEDIA FUSION Co.,Ltd. All rights reserved.