[S-EM12] Electric, magnetic, and electromagnetic survey technologies and the scientific achievements

[SEM12-01] UNDERSTANDING MAGMATIC SYSTEM OF UNZEN VOLCANO (NAGASAKI, SOUTHWEST JAPAN) INFERRED FROM BROAD-BAND MAGNETOTELLURIC OBSERVATION

*Agnis Triahadini¹, Koki Aizawa², Tasuku M. Hashimoto³, Kazunari Uchida², Yuto Yamamoto¹, Keita Chiba², Dan Muramatsu¹, Kanta Miyano¹, Yuta Kawamura¹, Satoru ANIYA¹, Ayumu Okubo¹ (1.Department of Earth and Planetary Sciences Graduate School of Sciences Kyushu University, 2.Institute of Seismology and Volcanology Faculty of Science Kyushu University, 3.Earthquake Research Institute The University of Tokyo)

Keywords:Unzen Volcano, Magma chamber, Resistivity structure, Magnetotelluric

Unzen volcano is an active lava domes complex which grows in Shimabara Peninsula, Nagasaki, Japan. Following the infamous 1991-1995 eruption, numerous studies had been conducted in Unzen Volcano. From the studies, the most widely accepted model is the main magmatic supply comes from 10 km west of the summit, at mid crustal depth under Chijiwa bay, where seismicity also intensified in this region. Prior to the last eruption, the magma was transported obliquely from below this area to eastern direction (Umakoshi et al 2001). Moreover, as pressure sources from geodetic data suggest, there are another possible sub magma chamber which is located in 5-6 km west of the summit (Kohno et al, 2008, Nishi et al 1999). Based on these facts, there must be a transport system to connect the main chamber to the secondary chamber and to the summit vent. However, to the present there is no resistivity structure image of whole area of Unzen volcano and Shimabara Peninsula. On an attempt to image Unzen volcano subsurface structure and its magmatic system, broadband magnetotelluric survey has been conducted between 2017-2020 covering Shimabara Peninsula and Unzen Volcano (Figure 1). In total, the electromagnetic data was collected from 98 sites. Some subsets of the data collected in west flank and summit area have been analyzed by Triahadini et al 2019 and Hashimoto et al 2020 respectively. However, both of the results are unable to image magma chamber. Since our last observation was finished by the end of December 2020, thus the data is currently under processing. Our resistivity structure will be used to improve the conceptual model of Unzen volcano magmatic system. On JPGU 2021 meeting, we would like to show our resistivity structure and compare it to the newest seismic tomography result and also hypocenter distribution prior to eruption until 2020.