TY - JOUR
T1 - Three-Dimensional Resistivity Structure of Iwo-Yama Volcano, Kirishima Volcanic Complex, Japan
T2 - Relationship to Shallow Seismicity, Surface Uplift, and a Small Phreatic Eruption
AU - Tsukamoto, K.
AU - Aizawa, K.
AU - Chiba, K.
AU - Kanda, W.
AU - Uyeshima, M.
AU - Koyama, T.
AU - Utsugi, M.
AU - Seki, K.
AU - Kishita, T.
N1 - Funding Information:
We thank H. Shimizu for supporting this work and constructive discussions. We thank the regional forest offices of Miyazaki and Kagoshima prefectures for permitting our observations. We used seismic data from Fukuoka District Meteorological Observatory, the Confidential manuscript submitted to Geophysical Research Letters University of Tokyo, and the National Research Institute for Earth Science and Disaster Resilience. We thank W. Siripunvaraporn for supplying his 3-D inversion code. We thank Y. Teguri, D. Muramatsu, A. Triahadini, Y. Yuasa, Y. Iwasa, K. Takeishi, Y. Hayashida, and A. Luthfian for their help with MT surveys. We thank A. Chave for providing his magnetotelluric analysis program. The geomagnetic data for remote reference processing were provided by the Kakioka Geomagnetic Observatory, Japan Meteorological Agency, and Geothermal Energy Research and Development Co. Comments from two anonymous reviewers and associate editor R. Carey were helpful in improving the manuscript. Data used in this study are available from the following website: https://archive.iii. kyushu-u.ac.jp/public/nYSogAjI8E5At 6AB7MxmitHyvx9GthSGjlA0w3f8vreT. We used the computer systems of the Earthquake and Volcano Information Center at the Earthquake Research Institute, University of Tokyo. This study was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its “Earthquake and Volcano Hazards Observation and Integrated Program for Next Generation Volcano Research and Human Resource Development.
Funding Information:
We thank H. Shimizu for supporting this work and constructive discussions. We thank the regional forest offices of Miyazaki and Kagoshima prefectures for permitting our observations. We used seismic data from Fukuoka District Meteorological Observatory, the Confidential manuscript submitted to Geophysical Research Letters University of Tokyo, and the National Research Institute for Earth Science and Disaster Resilience. We thank W. Siripunvaraporn for supplying his 3-D inversion code. We thank Y. Teguri, D. Muramatsu, A. Triahadini, Y. Yuasa, Y. Iwasa, K. Takeishi, Y. Hayashida, and A. Luthfian for their help with MT surveys. We thank A. Chave for providing his magnetotelluric analysis program. The geomagnetic data for remote reference processing were provided by the Kakioka Geomagnetic Observatory, Japan Meteorological Agency, and Geothermal Energy Research and Development Co. Comments from two anonymous reviewers and associate editor R. Carey were helpful in improving the manuscript. Data used in this study are available from the following website: https://archive.iii.kyushu-u.ac.jp/public/nYSogAjI8E5At6AB7MxmitHyvx9GthSGjlA0w3f8vreT. We used the computer systems of the Earthquake and Volcano Information Center at the Earthquake Research Institute, University of Tokyo. This study was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its “Earthquake and Volcano Hazards Observation and Integrated Program for Next Generation Volcano Research and Human Resource Development.
Publisher Copyright:
©2018. American Geophysical Union. All Rights Reserved.
PY - 2018/12/16
Y1 - 2018/12/16
N2 - Iwo-yama volcano, part of the Kirishima Volcanic Complex, has recently shown signs of unrest. We conducted a hypocenter relocation of shallow earthquakes and broadband magnetotelluric measurements around Iwo-yama. Three-dimensional inversion of magnetotelluric data revealed an electrically conductive layer that is interpreted as a hydrothermally altered clay-dominated unit. Shallow earthquakes occur beneath this layer, suggesting that it controls the location of seismicity. The base of the layer corresponds to the depth of a pressure source identified by a leveling survey. These observations suggest that the supply of high-temperature fluids has increased over time beneath Iwo-yama, causing an increase in pore pressure beneath the clay-rich layer and resulting in tectonic earthquakes and ground inflation. Increased upwelling of fluids through a fracture in the clay-rich layer may have caused a vigorous liquid-gas phase transition near the surface, which in turn might have led to the small phreatic eruption on 19 April 2018.
AB - Iwo-yama volcano, part of the Kirishima Volcanic Complex, has recently shown signs of unrest. We conducted a hypocenter relocation of shallow earthquakes and broadband magnetotelluric measurements around Iwo-yama. Three-dimensional inversion of magnetotelluric data revealed an electrically conductive layer that is interpreted as a hydrothermally altered clay-dominated unit. Shallow earthquakes occur beneath this layer, suggesting that it controls the location of seismicity. The base of the layer corresponds to the depth of a pressure source identified by a leveling survey. These observations suggest that the supply of high-temperature fluids has increased over time beneath Iwo-yama, causing an increase in pore pressure beneath the clay-rich layer and resulting in tectonic earthquakes and ground inflation. Increased upwelling of fluids through a fracture in the clay-rich layer may have caused a vigorous liquid-gas phase transition near the surface, which in turn might have led to the small phreatic eruption on 19 April 2018.
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U2 - 10.1029/2018GL080202
DO - 10.1029/2018GL080202
M3 - Article
AN - SCOPUS:85058473812
SN - 0094-8276
VL - 45
SP - 12,821-12,828
JO - Geophysical Research Letters
JF - Geophysical Research Letters
IS - 23
ER -