Solidified magma reservoir derived from seismic exploration in the Aira caldera, southern Kyushu, Japan
Author:
Miyamachi Hiroki1ORCID, Yakiwara Hiroshi1, Kobayashi Reiji1, Hirano Shuichiro1, Kubo Takeshi1, Souda Masakazu1, Sakao Kenyu1, Unno Naohiro1, Matsushima Takeshi2, Uchida Kazunari2, Miyamachi Rintaro2, Isoda Kenshin2, Teguri Yoshiko2, Kamiya Yoshinosuke2, Triahadini Agnis2, Shimizu Hiroshi2, Katao Hiroshi3, Shibutani Takuo3, Tameguri Takeshi3, Yamashita Yusuke3, Miura Tsutomu3, Nakagawa Jun3, Yoneda Itaru3, Kato Shinya3, Takishita Kosei3, Nakai Kazuho3, Maeda Yuta4, Watanabe Toshiki4, Horikawa Shinichiro4, Matsushiro Kenjiro4, Okuda Takashi4, Tsuji Shuhei4, Sogawa Naoki4, Hasegawa Daima4, Nakahigashi Kazuo5, Kurashimo Eiji6, Yamada Tomoaki6, Abe Hideji6, Ando Miwako6, Tanaka Shinichi6, Ikezawa Satoshi6, Iwasaki Takaya6, Shinohara Masanao6, Sato Toshinori7, Yamamoto Mare8, Azuma Ryosuke8, Hirahara Satoshi8, Nakayama Takashi8, Suzuki Syuichi8, Otomo Shuhei8, Hino Ryota8, Tsutsui Tomoki9, Inoue Yusuke9, Takei Ryuichi9, Tada Yuya9, Takahashi Hiroaki10, Murai Yoshio10, Aoyama Hiroshi10, Ohzono Mako10, Shiina Takahiro10, Takada Masamitsu10, Ichiyanagi Masayoshi10, Yamaguchi Teruhiro10, Ono Natsuki10, Saito Kazuma10, Ito Chihiro10, Susukida Yuuki10, Nakagaki Tatsuya10, Tanaka Yasuhisa11, Akinaga Yasuhiko12
Affiliation:
1. Kagoshima University Faculty of Science Graduate School of Science and Engineering: Kagoshima Daigaku Rigakubu Daigakuin Rikogaku Kenkyuka 2. Kyushu University Faculty of Sciences Graduate School of Sciences: Kyushu Daigaku Rigaku Kenkyuin Rigakufu Rigakubu 3. Kyoto University: Kyoto Daigaku 4. Nagoya University: Nagoya Daigaku 5. Tokyo University of Marine Science and Technology: Tokyo Kaiyo Daigaku 6. University of Tokyo: Tokyo Daigaku 7. Chiba University: Chiba Daigaku 8. Tohoku University: Tohoku Daigaku 9. Akita University: Akita Daigaku 10. Hokkaido University: Hokkaido Daigaku 11. JGI Inc. 12. Hanshin Cooporation Co. Ltd.
Abstract
Abstract
Seismic exploration was conducted along a profile running through the Aira caldera located in southern Kyushu, Japan. The caldera was formed by an ignimbrite eruption approximately 30 ka BP, namely, the “AT eruption,” which produced the Ito ignimbrite and widespread Aira-Tanzawa ash. This analysis aimed to clarify the detailed P-wave velocity structure beneath the caldera. Accordingly, 829 inland seismic stations and 42 ocean bottom seismographs were deployed along the 195 km-long seismic profile to record seismic waves generated by numerous controlled seismic sources. A detailed velocity structure of the active Aira caldera was successfully obtained to depths of 20 km through travel-time tomography. A substantial structural difference was observed in the thicknesses of the low-velocity zones between the eastern and western sides in the shallowest region of the Aira caldera, suggesting that the Aira caldera is composed of at least two calderas: the AT caldera associated with the AT eruption, and the Wakamiko caldera associated with the post-AT eruption. Perhaps the most interesting feature of the caldera structure is the existence of a substantially high-velocity zone at depths of 6–11 km beneath the center area of the AT caldera, which can be interpreted as the cooled and solidified magma reservoir formed during or after the AT eruption. In addition, a low-velocity region with approximately 15 km depths indicated a deep magma reservoir. Based on these novel and past research results, a new magma supply model in the Aira caldera was proposed. Further, the spatial distribution of the magma reservoir associated with the AT eruption 30 ka BP was estimated, while the future possibility of larger eruptions in this caldera was discussed.
Publisher
Research Square Platform LLC
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