Japan Geoscience Union Meeting 2022

Presentation information

[J] Poster

S (Solid Earth Sciences ) » S-VC Volcanology

[S-VC31] Active Volcanism

Thu. Jun 2, 2022 11:00 AM - 1:00 PM Online Poster Zoom Room (25) (Ch.25)

convener:Yuta Maeda(Nagoya University), convener:Fukashi Maeno(Earthquake Research Institute, University of Tokyo), Takeshi Matsushima(Institute of Seismology and Volcanology, Faculty of Science, Kyushu University)

11:00 AM - 1:00 PM

[SVC31-P18] Amphibious passive seismic observation at Kikai submarine caldera

*Yojiro Yamamoto1, Aki Ito1, Yasushi Ishihara1, Masayuki Obayashi1, Satoru Tanaka1, Haruhisa Nakamichi2, Hiroshi Yakiwara3, Yukihiro Nakatani3, Hiroko Sugioka4,5, Hironori Otsuka4, Tetsuo Matsuno4, Nobukazu Seama5,4 (1.Japan Agency for Marine-Earth Science and Technology, 2.Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University, 3.Nansei-Toko Observatory for Earthquakes and Volcanoes, Kagoshima University, 4.Kobe Ocean-Bottom Exploration Center (KOBEC), 5.Department of Planetology, Kobe University)

Keywords:Kikai submarine caldera, Seismic observation, Seismic velocity structure

Kikai submarine caldera is located to the south of the Kyushu Island, and its last eruption occurred at 7.3 ka. The 7.3-ka Akahoya super-eruption devastated the lives of the Jomon people, especially in southern Kyushu. Post-caldera volcanic activity was also active and formed Iwo-Dake, Inamura-Dake, and Showa Iwo-Jima Island. However, both the location and spatial extent of the magma chamber is still unknown due to the sparse observation network.
To clarify the magma supply system beneath the Kikai submarine caldera, we have started the passive seismic observations both offshore and onshore since Autumn of 2020. We deployed 25 short-period ocean bottom seismometers (SPOBSs) and 12 broadband ocean bottom seismometers (BBOBSs) in and around the Kikai submarine caldera during the cruise of R/V KAIREI. Onshore seismic stations were deployed in five islands; Take-Shima, Satsuma Iwo-Jima, Kuro-Shima, Tanegashima, and Yakushima. All the land stations are equipped the broadband seismometer and three of them have telemeter systems. Unfortunately, one SPOBSs popped up by itself and were washed onto the coast in June 2021. The recovery cruise for SPOBS was conducted in July 2021. Although five SPOBS could not be recovered, the other 19 SPOBSs were recovered in 2021 by R/V KAIMEI. Both BBOBS and onshore observations will continue until next summer.
Now we are checking the currently available SPOBS and onshore data. By comparing the JMA unified catalog, we confirmed that our seismic data successfully record the earthquakes that occurred around the Kikai submarine caldera, especially intermediate-depth earthquakes beneath the Satsuma Peninsula and forearc earthquakes around Tanegashima. Using the first arrival time data of these earthquakes and previous seismic observation in this area, we will present the preliminary results on the hypocenter relocation and seismic velocity structure model in this presentation.

Acknowledgement: We thank the Japan Meteorological Agency for providing the earthquake catalog and arrival-time data used in this study. Mishima Village, Nishino-omote City, and Yakushima Town kindly cooperated for our onshore observations.