Japan Geoscience Union Meeting 2016

Presentation information


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

[S-EM35] Electromagnetic Induction in the Earth and Planetary Interiors, and Tectono-Electromagnetism

Wed. May 25, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Masahiro Ichiki(Graduate School of Science, Tohoku University), Mitsuru Utsugi(Aso Volcanological Laboratory, Institute for Geothermal Sciences, Graduate School of Science, Kyoto University)

5:15 PM - 6:30 PM

[SEM35-P05] Crustal structure beneath the whole of Aso caldera by using 3-D electrical resistivity imaging

*Maki Hata1, Shinichi Takakura1, Nobuo Matsushima1, Takeshi Hashimoto2 (1.Advanced Industrial Science and Technology, 2.Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University)

Aso caldera with up to 25 km across, which is situated at the Kyushu Island in the Southwest Japan Arc, was formed by four huge eruptions with hundreds km3 of deposits 90–300 ka. After the caldera formation, a number of volcanic cones were formed at the central part of the caldera. Naka-dake, one of the post-caldera cones, has periodically erupted in historical age. A magmatic eruption occurred in Nov. 2014 after 22 years' absence and a phreatomagmatic eruption occurred in Sep. 2015 after 21 years' absence at Naka-dake. Recent research results from the seismic tomography and the electrical resistivity tomography have suggested magma chambers at several depths in the crust beneath Aso caldera. Further research of the crustal structure beneath Aso caldera, which experienced the huge eruptions, are required to verify the size and position of the magma chambers.
We carried out a Magnetotelluric (MT) survey at the entire Aso caldera from Nov. to Dec. 2015 and performed three-dimensional (3-D) inversion analyses to obtain a crustal-scale electrical resistivity structure (model) by using the period range between 0.005 and 2,380 s of MT data for 50 sites. Moreover, we performed another 3-D inversion analyses by using the period range between 0.007 and 1,365 s of MT data for 68 sites, which were obtained by surveys around Naka-dake from 1997 to 2001 [Takakura et al., 2000; Hashimoto et al., 2002; Asaue et al., 2006]. In the inversion process, we use a parallelized DASOCC inversion code [e.g., Siripunvaraporn et al., 2004; Siripunvaraporn and Egbert, 2009]. In this presentation, we will show the two crustal-scale resistivity models beneath Aso caldera, which were obtained by using the above-mentioned two MT data sets.