MF研究者総覧

研究者データベース

詳細
田中　良(タナカ　リヨウ)
理学研究院　附属地震火山研究観測センター
助教
researchmap個人ページ
Last Updated :2024/05/09

基本情報

所属

  • 理学研究院　附属地震火山研究観測センター

職名

  • 助教

学位

  • 博士（理学）（北海道大学）

ホームページURL

科研費研究者番号

  • 30804926

ORCID ID

J-Global ID

研究キーワード

  • 火山物理学   熱水流動数値計算   火山測地学   熱観測   ドローン   火山の熱水系   火山噴火予知   

研究分野

  • 自然科学一般 / 固体地球科学

担当教育組織

職歴

  • 2019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 助教
  • 2017年04月 - 2019年03月 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 非常勤研究員

学歴

  • 2014年04月 - 2017年03月   北海道大学大学院理学院 博士後期課程
  • 2012年04月 - 2014年03月   北海道大学大学院理学院 修士課程
  •         - 2012年03月   北海道大学理学部地球惑星科学科

所属学協会

  • 日本火山学会   日本地球惑星科学連合   

研究活動情報

論文

  • Kensuke Yamaguchi, Ryo Tanaka, Masaaki Morita, Toshiya Mori, Ryunosuke Kazahaya
    Frontiers in Earth Science 11 2023年05月18日 
    Introduction: Monitoring the volcanic activity of a potentially hazardous volcano is essential for eruption warning and hazard mitigation. The SO2 flux from the volcano is one of the most important measures to understand its activity. Mount Tokachi, in Japan, is an active volcano that experienced three magmatic explosive eruptions in the 20th century (in 1926, 1962, and 1988–1989). Since 2006, geodetic observations have captured ground deformation, suggesting an inflation beneath the main crater. Moreover, since 2020 daily visual observations have detected the increase in plume heights and the occurrence of volcanic glow at the main crater. The high-time-resolution estimation of SO2 flux will help monitor the activity of Mount Tokachi and clarify the associating mechanisms. Furthermore, satellite remote sensing can estimate the vertical column density (VCD) of sulfur dioxide (SO2), enabling the daily determination of SO2 flux without the need to visit the site. Due to the improved spatial resolution, the TROPOspheric Monitoring Instrument (TROPOMI) has advanced satellite-based volcanic gas flux measurements.Methods: We have analyzed the available TROPOMI data and conducted ground-based observations to estimate the SO2 flux from Mount Tokachi at 100–2,000 tons/day.Result and Discussion: The average annual SO2 flux has been increasing since 2021, on par with the increase in plume height and volcanic glow. TROPOMI data enabled quantification of the annual SO2 flux, with a sufficient temporal resolution to monitor the volcanic activity at Mount Tokachi. However, a high flux, such as in excess of 2,000 tons/day, was observed in the winter season. The flux from the satellite data was similar to that from ground-based observations during the summer. However, a seasonal change in flux from the satellite data was observed in winter, with the flux being larger than that in summer, possibly because the flux increases during winter. Another possible reason is the influence of snow cover on satellite observations due to its high surface reflectance. We reanalyzed some TROPOMI data during the winter, in which the ground snow cover was misidentified as clouds at low altitudes. This procedure suppresses the error caused by the high surface reflectance due to winter snow coverage and improves the quality of the annual SO2 flux from satellite observations. This methodology is applicable to other high-latitude or high-altitude volcanoes during specific seasons characterized by frequent fluctuations in snow cover conditions.
  • Inoue, T, Hashimoto, T, Tanaka, R, Yamaya, Y
    Earth, Planets and Space 74 114  2022年12月 [査読有り][通常論文]
  • Ryo Tanaka
    Journal of Disaster Research 17 5 639 - 643 2022年08月01日 [査読有り]
     
    To understand a field of volcanic activity, a survey on the Earth’s subsurface structure is helpful. In particular, a magnetotelluric survey can image the subsurface structure necessary for volcanic disaster prevention because it is sensitive to high-temperature areas and areas where fluid and clay minerals exist. In 3-D magnetotelluric inversion using the data observed near volcanoes and the coastline, the topography and sea around the survey area need to be considered. Therefore, constructing a mesh of the analysis area by automatically using topography and bathymetry data is necessary. Additionally, the estimated subsurface structure should be compared to the sources of variation estimated from other physical observations, such as earthquakes, ground deformation, and changes in the geomagnetic total field, for interpretation. This study introduces a simple and easy-to-operate graphical pre- and post-processor developed to support the resistivity structure analysis of a volcano and the nearby coastline. In the developed software, the pre-process indicates the mesh construction, and the post-process indicates result derivation, file construction for the sensitivity tests, and file exportation to compare the inversion results with other measured quantities. This pre- and post-process can be performed easily on the same window of the software.
  • Yuki Susukida, Kei Katsumata, Masayoshi Ichiyanagi, Mako Ohzono, Hiroshi Aoyama, Ryo Tanaka, Masamitsu Takada, Teruhiro Yamaguchi, Kazumi Okada, Hiroaki Takahashi, Shin’ichi Sakai, Satoshi Matsumoto, Tomomi Okada, Toru Matsuzawa, Hiroki Miyamachi, Shuichiro Hirano, Yoshiko Yamanaka, Shinichiro Horikawa, Masahiro Kosuga, Hiroshi Katao, Yoshihisa Iio, Airi Nagaoka, Noriko Tsumura, Tomotake Ueno
    Earth, Planets and Space 73 1 2021年12月 [査読有り]
     
    AbstractThe tectonic stress field was investigated in and around the aftershock area of the Hokkaido Eastern Iburi earthquake (MJMA = 6.7) occurred on 6 September 2018. We deployed 26 temporary seismic stations in the aftershock area for approximately 2 months and located 1785 aftershocks precisely. Among these aftershocks, 894 focal mechanism solutions were determined using the first-motion polarity of P wave from the temporary observation and the permanent seismic networks of Hokkaido University, Japan Meteorological Agency (JMA), and High Sensitivity Seismograph Network Japan (Hi-net). We found that (1) the reverse faulting and the strike-slip faulting are dominant in the aftershock area, (2) the average trend of P- and T-axes is 78° ± 33° and 352° ± 51°, respectively, and (3) the average plunge of P- and T-axes is 25° ± 16° and 44° ± 20°, respectively: the P-axis is close to be horizontal and the T-axis is more vertical than the average of the P-axes. We applied a stress inversion method to the focal mechanism solutions to estimate a stress field in the aftershock area. As a result, we found that the reverse fault type stress field is dominant in the aftershock area. An axis of the maximum principal stress (σ1) has the trend of 72° ± 7° and the dipping eastward of 19° ± 4° and an axis of the intermediate principal stress (σ2) has the trend of 131° ± 73° and the dipping southward of 10° ± 9°, indicating that both of σ1- and σ2-axes are close to be horizontal. An axis of the minimum principal stress (σ3) has the dipping westward of 67° ± 6° that is close to be vertical. The results strongly suggest that the reverse-fault-type stress field is predominant as an average over the aftershock area which is in the western boundary of the Hidaka Collision Zone. The average of the stress ratio R = (σ1 − σ2)/(σ1 − σ3) is 0.61 ± 0.13 in the whole aftershock area. Although not statistically significant, we suggest that R decreases systematically as the depth is getting deep, which is modeled by a quadratic polynomial of depth.
  • Ryo Tanaka, Yusuke Yamaya, Makoto Tamura, Takeshi Hashimoto, Noritoshi Okazaki, Ryo Takahashi, Toru Mogi
    Earth, Planets and Space 73 1 2021年12月 [査読有り]
     
    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.
  • 工藤千聖, 青山 裕, 田中 良
    北海道大学地球物理学研究報告 83 103 - 114 北海道大学大学院理学研究院 2020年03月19日 [査読無し][通常論文]
  • 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 83 25 - 48 北海道大学大学院理学研究院 2020年03月19日
  • Shohei Narita, Makoto Murakami, Ryo Tanaka
    Earth, Planets and Space 71 1 2019年12月30日 
    Abstract The phreatic eruption of Mount Ontake in 2014 caused local-scale subsidence and a mass discharge of water–vapor plumes from vents. A previous study of InSAR data analysis modeled the local subsidence as a deflation of a shallow hydrothermal reservoir (~ 500 m beneath the vents), and speculated that it was associated with plume emission continuing just after the eruption. In addition, combination of the InSAR and GNSS data implies that another, deeper deflation source (~ 3–6 km beneath the vents) contributes to the baseline contraction of the GNSS data. In this study, we estimated daily mass flux of the emitting plumes using photographed images, and compared the temporal behavior of the discharged mass with that of deflation of the two sources in order to clarify their association. The temporal profiles of the shallow deflation volume and the discharge mass both show evidence of decay, but with different characteristics; the deflation volume progress was approximated by a single exponential decay with a long relaxation time (379–641 days), whereas the discharge mass displayed a sum of a linear trend and an exponential decay with shorter relaxation time (47 days). This discrepancy, along with GNSS data, suggests the contribution of a deep deflation source with a short relaxation time (20–40 days). Estimation of mass balance between the emitting plume and fluids discharged from both shallow and deep sources revealed that more than 70% of the discharged mass came from the deep source. Based on the estimated mass balance, phase state of the shallow reservoir was estimated as a single-phase, liquid-rich reservoir. The fast decay of the deep deflation may reflect rapid depressurization due to violent fluid discharge at the onset of the eruption. In contrast, the slow decay of the shallow deflation suggests that it had a minor role in the eruption. However, such a wet reservoir has the potential to induce volcanic hazard such as snow-melting lahar for future eruptions, requiring monitoring the volcano, which will probably shift to pre-eruptive re-pressurized phase, until the future eruption.
  • Kei Katsumata, Masayoshi Ichiyanagi, Mako Ohzono, Hiroshi Aoyama, Ryo Tanaka, Masamitsu Takada, Teruhiro Yamaguchi, Kazumi Okada, Hiroaki Takahashi, Shin'ichi Sakai, Satoshi Matsumoto, Tomomi Okada, Toru Matsuzawa, Shuichiro Hirano, Toshiko Terakawa, Shinichiro Horikawa, Masahiro Kosuga, Hiroshi Katao, Yoshihisa Iio, Airi Nagaoka, Noriko Tsumura, Tomotake Ueno, Koji Miyakawa, Shin'ichi Tanaka, Miwako Ando, Naoki Uchida, Ryosuke Azuma, Ryota Takagi, Keisuke Yoshida, Takashi Nakayama, Satoshi Hirahara, Yoshiko Yamanaka, Yuta Maeda, Shuichiro Hirano, Hiroki Miyamachi, Hiroshi Yakiwara, Takuto Maeda, Masahiro Shimazaki, Youichi Asano
    EARTH PLANETS AND SPACE 71 2019年12月 [査読有り][通常論文]
     
    The Hokkaido Eastern Iburi earthquake (M-JMA=6.7) occurred on September 6, 2018, in the Hokkaido corner region where the Kurile and northeastern Japan island arcs meet. We relocated aftershocks of this intraplate earthquake immediately after the main shock by using data from a permanent local seismic network and found that aftershock depths were concentrated from 20 to 40km, which is extraordinarily deep compared with other shallow intraplate earthquakes in the inland area of Honshu and Kyushu, Japan. Further, we found that the aftershock area consists of three segments. The first segment is located in the northern part of the aftershock area, the second segment lies in the southern part, and the third segment forms a stepover between the other two segments. The hypocenter of the main shock, from which the rupture initiated, is located on the stepover segment. The centroid moment tensor solution for the main shock indicates a reverse faulting, whereas the focal mechanism solution determined by using the first-motion polarity of the P wave indicates strike-slip faulting. To explain this discrepancy qualitatively, we present a model in which the rupture started as a small strike-slip fault in the stepover segment of the aftershock area, followed by two large reverse faulting ruptures in the northern and southern segments.
  • Takeshi Hashimoto, Wataru Kanda, Yuichi Morita, Midori Hayakawa, Ryo Tanaka, Hiroshi Aoyama, Makoto Uyeshima
    Journal of Disaster Research 14 4 580 - 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.
  • ロシア・カムチャツカ半島アバチンスキー火山での傾斜観測
    高橋浩晃, 青山裕, 大園真子, 田中良, 伊藤ちひろ, 渡邉早姫, 松島健, 山下裕亮, 宮町宏樹, 奥山哲, ゴルディエフ エフゲニー, ムラビヨフ ヤロスラフ, マグースキン キリル, マリック ナタリヤ, ミノロフ イワン, チェブロフ ダニラ
    北海道大学地球物理学研究報告 82 11 - 18 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 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.].
  • Hashimoto, T., Terada, A., Tanaka, R.
    Earth, Planets and Space 70 1 2018年 [査読有り][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]
  • Ryo Tanaka, Takeshi Hashimoto, Nobuo Matsushima, Tsuneo Ishido
    EARTH PLANETS AND SPACE 69 1 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.
  • Toshiya Mori, Takeshi Hashimoto, Akihiko Terada, Mitsuhiro Yoshimoto, Ryunosuke Kazahaya, Hiroshi Shinohara, Ryo Tanaka
    EARTH PLANETS AND SPACE 68 1 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.
  • 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.

その他活動・業績

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 : 2023年04月 -2026年03月 
    代表者 : 高橋 良, 竹内 晋吾, 田中 良, 上澤 真平, 藤原 寛
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2021年07月 -2024年03月 
    代表者 : 青山 裕, 西村 太志, 田中 良
     
    初年度である2021年度は，北海道南部のしかべ間歇泉で本研究課題の開始前から実施している多項目連続観測を継続して噴出孔内の映像撮影や圧力測定を試みたほか，鬼首間歇泉で取得した熱赤外カメラ及び空気振動観測のデータ解析，霧島硫黄山の噴気観測，地下構造の深部からの熱水供給率を変化させたときの熱水流動の応答に関する数値計算などを実施した． しかべ間歇泉では，間歇泉噴出孔の保守業者の厚意により，6月および9月の作業時に業者所有の孔内撮影用カメラを間歇泉内に挿入し，孔内の状況把握や孔底深度の計測，噴出時の気泡発生状況の動画撮影等を行った．この調査により，掘削深度は約27mであり，ケーシング部分は上部の20mで下部の約7mは裸孔となっていることが始めて確認された．また，井戸の下端には熱水溜まりのような空洞は存在せず，ケーシング下端や裸孔部分の亀裂から井戸内に高温水が流入していることが明らかになった．1月には研究費で購入した圧力センサーを用いて噴出中の孔内圧力を測定し，噴出サイクルを通した井戸内圧力の時系列データを取得した．この調査時には，噴出ごとの熱水噴出体積の推定を試み，過去に見積もられた400L程度であることを確認した． 鬼首間歇泉では，間欠泉噴出時に観測した熱赤外映像および空気振動観測のデータ解析を進めた．熱赤外映像は時間的な差分を取ることで短周期変動を強調し，熱水の上方への噴出を調べた結果，周期1秒以下の調和振動が見られることを見出した．空気振動にも同様の振動が見られることから，噴出孔の極浅部で共鳴現象が起きていることが示唆された． 宮崎県の霧島硫黄山では，自然の噴気について熱赤外映像の試験観測を行った．予備的な解析では，連続的な蒸気を噴出する噴気にも調和振動的な振る舞いが認められることから，間歇泉現象や噴気現象には浅部に共鳴現象を励起する類似のプロセスがあることが示唆された．

教育活動情報

主要な担当授業

  • 自然史科学特別講義Ⅱ
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 火山学，地球物理学，地質学，岩石学，地球化学
  • 自然史科学特別講義Ⅰ
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 火山学，地球物理学，地質学，岩石学，地球化学
  • 地球計測実習
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 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
  • 地球惑星科学のための古典力学
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 力学, 解析力学, ラグランジアン, ラグランジュの運動方程式，ハミルトニアン，ハミルトンの運動方程式，変分原理
  • 地球惑星科学のための古典力学演習
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 力学, 解析力学, ラグランジアン, ハミルトニアン, 変分原理, 最小作用の原理

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