11:00 〜 13:00
[SVC31-P18] 鬼界海底カルデラにおける海陸自然地震観測
キーワード：鬼界海底カルデラ、地震観測、地震波速度構造
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.
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.