JpGU-AGU Joint Meeting 2020

Presentation information

[E] Oral

S (Solid Earth Sciences ) » S-EM Earth's Electromagnetism

[S-EM20] Electric and Electromagnetic survey technologies and the scientific achievements: Recent advances

convener:Kiyoshi Baba(Earthquake Research Institute, The University of Tokyo), Tada-nori Goto(Graduate School of Life Science, University of Hyogo), Toshihiro Uchida(National Institute of Advanced Industrial Science and Technology), Toru Mogi(Faculty of Science, Tokyo Institute of Technology)

[SEM20-04] Anatomy of Active Volcanic Edifice at the Kusatsu-Shirane Volcano, Japan, by Magnetotellurics: Hydrothermal Implications for Volcanic Unrests

Kuo Hsuan Tseng1, *Yasuo Ogawa1, Nurhasan Nurhasan1, Sabri Bülent Tank1, Yoshimori Honkura1, Naoto Ujihara1, Akihiko Terada1, Yoshiya Usui1, Wataru Kanda1 (1.Volcanic Fluid Research Center, School of Science, Tokyo Institute of Technology)

Keywords:Phreatic eruption, volcanic unrest, Magnetotelluric method, clay cap, brine

We aimed to perform three-dimensional imaging of the underlying geothermal system to a depth of 2km using magnetotellurics (MT). We deployed 91 MT sites focusing around the peak area of 2km x 2km with typical spacings of 200m. The full tensor impedances and the magnetic transfer functions were inverted, using an unstructured tetrahedral finite element code to include the topographic effect. The final model showed (1) impermeable clay cap as the near surface conductor, (2) brine reservoir as a deep conductor at a depth of 1.5 km from the surface, and (3) a vertical conductor connecting the deep conductor to the clay cap associated with the seismicity, which implies a fluid/gas path. The past magnetization/demagnetization sources and the inflation source of the 2014 unrest are located just below the clay-cap, consistent with the clay capped geothermal model.