Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

S (Solid Earth Sciences ) » S-VC Volcanology

[S-VC39] Hydrothermal systems of volcanoes

Mon. May 27, 2019 10:45 AM - 12:15 PM IC (2F)

convener:Yasuhiro Fujimitsu(Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University), Wataru Kanda(Volcanic Fluid Research Center, School of Science, Tokyo Institute of Technology), Takeshi Ohba(Department of chemistry, School of Science, Tokia University), Chairperson:Yasuhiro Fujimitsu(Faculty of Engineering, Kyushu University), Takeshi Ohba, Wataru Kanda

11:00 AM - 11:15 AM

[SVC39-08] Constraining electrical resistivity structure of volcanoes using multiphase flow modelling: an example of Miyake-jima

*Marceau Gresse1, Makoto Uyeshima1, Takao Koyama1, Maki Hata1, Hideaki Hase2, Koki Aizawa3, Yusuke Yamaya4, Yoichi Sasai5, Jacques Zlotnicki6, Tawat Rung-Arunwan1, Hideki Ueda7 (1.Earthquake Research Institute, The University of Tokyo, Tokyo, Japan, 2.Geothermal Energy Research & Development Co., Ltd., Tokyo, Japan, 3.Institute of Seismology and Volcanology, Faculty of Science, Kyushu University, Fukuoka, Japan., 4.Planning Division, National Institute of Advanced Industrial Science and Technology, Tokyo, Japan, 5.Earthquake Prediction Research Centre, Tokai University, Shizuoka, Japan, 6.CNRS, OPGC-UMR6524, Aubière, France, 7.National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan)

Keywords:Hydrothermal system, Magnetotellurics, Miyake-jima, multiphase flow, electrical resistivity, alteration

Measuring the electrical resistivity of rocks is a powerful and reliable method used to investigate volcanic edifices at depth. The electrical resistivity has two main contributions: (i) the conduction in the bulk pore fluid, associated to saturation, the ionic strength, and temperature of pore water, and (ii) the surface conductivity, related to the formation of secondary minerals. In volcanic environments, these two contributions are controlled by numerous interactions between hydrology, geology, tectonic settings and magmatic forcing. As a consequence, the evaluation of electrical resistivity images is strongly non-unique, and its interpretation remains complex.

Here, we propose a new approach to address this issue. First, we performed a 3-D electrical resistivity imagery of the Miyake-jima volcano using Magnetotellurics. Next, we combined the resistivity model obtained with hypocenters distribution. We revealed the sharp boundary between the saturated and unsaturated region, and a large conductive hydrothermal system connected to the main fumarolic area through a fractured region. Finally, we created a multiphase flow model of the volcano that constrains the resistivity model in term of temperature, fluid content and alteration.