[S-EM14] Electromagnetic Induction in the Earth and Planetary Interiors, and Tectono-Electromagnetism

[SEM14-03] 3-D resistivity models beneath Aso caldera by new and old Network-MT dipole data arranged into reticular shapes

*Maki Hata¹, Makoto Uyeshima¹, Mitsuru Utsugi², Nobuo Matsushima³, Yoshikazu Tanaka, Takeshi Hashimoto⁴, Ryokei Yoshimura⁵, Naoto Oshiman⁵ (1.Earthquake Research Institute, the University of Tokyo , 2.Aso Volcanological Laboratory, Institute for Geothermal Sciences, Graduate School of Science, Kyoto University, 3.Geological Survey of Japan, 4.Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University, 5.Disaster Prevention Research Institute, Kyoto University)

Keywords:3-D electrical resistivity models, Network-MT data, Aso caldera, magma supply system

Mt. Aso, an active Quaternary volcano, with a large caldera lie at the Beppu-Shimabara graben in the island of Kyushu. Aso caldera was formed at the central part of the graben by a series of huge eruptions, with a volcanic explosivity index of 7, during 270–90 ka. A post-caldera cone of Naka-dake in Aso caldera is a quite active volcano, at which magmatic and phreatomagmatic eruptions occurred during 2014–2016 and ash eruptions (emissions) have continued since July 2019. In and around Aso caldera, network-MT surveys for measuring the electric potential difference (the electric field) were carried out during 1993–1998 by using long metallic wires/dipoles of the commercial telephone company's networks [e.g., Uyeshima et al., 1995; Tanaka et al., 1998; Hashimoto et al., 1999; Hata et al., 2015]. We determined two components of network-MT response functions between the potential differences for respective dipoles and the two horizontal components of the magnetic field at the Kanoya Geomagnetic Observatory. On the other hand, we newly performed network-MT surveys at Aso caldera during 2019–2020 and determined response functions. Three-dimensional (3-D) inversion analyses were performed by using two data sets in a period up to tens of thousands s for obtaining resistivity models beneath Aso caldera in a crustal depth scale. In the inversion analyses, we used a data-space inversion code, which can be considered the length and direction of respective dipoles [e.g., Siripunvaraporn et al., 2004]. Moreover, the dipoles are distributed as to cover Aso caldera into reticular formation in order to obtain well-resolved 3-D models. In this presentation, we discuss a magma supply system beneath Aso caldera, which are inferred from the two 3-D resistivity models based on the new and old Network-MT data.