{"id":6668,"date":"2025-03-12T17:43:31","date_gmt":"2025-03-12T08:43:31","guid":{"rendered":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/?p=6668"},"modified":"2025-03-12T17:55:56","modified_gmt":"2025-03-12T08:55:56","slug":"seismic-activity-around-shallow-plate-boundary-near-westernmost-nankaitrough-revealed-by-ocean-bottom-seismometer-observation","status":"publish","type":"post","link":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/research\/6668\/","title":{"rendered":"Seismic activity around shallow plate boundary near westernmost Nankai Trough revealed by ocean bottom seismometer observation"},"content":{"rendered":"\n<p class=\"has-text-align-center\">Ching-Yu Hu 1,2 , Masanao Shinohara 1 , Yusuke Yamashita 3 , Takashi Tonegawa 4 , <br>Tomoaki Yamada 1,Takeshi Akuhara 1 , Kimihiro Mochizuki 1 \u2028<\/p>\n\n\n\n<p class=\"has-text-align-center\">1 Earthquake Research Institute, The University of Tokyo, 2 Graduate School of Science, The University of<br>Tokyo, \u2028 3 Disaster Prevention Research Institute, Kyoto University, 4 Japan Agency for Marine-Earth\u3000Science and Technology<br>Earth, Planets and Space, 76(1), 168. <a href=\"https:\/\/doi.org\/10.1186\/s40623-024-02122-4\">https:\/\/doi.org\/10.1186\/s40623-024-02122-4<\/a><\/p>\n\n\n\n<p>\u3000Seafloor seismic observations in the Hyuga-nada region were conducted during 2015\u20132016, 2017\u20132018, and 2022. Hypocenters of fast earthquakes were first determined using a 1-D velocity structure with station corrections applied for structural heterogeneity beneath each OBS station. Events were then relocated using the double-difference technique, and focal mechanisms were estimated from first-arrival polarity data.<br>\u3000<br>\u3000Relocation results indicates that earthquakes occurred within the subducting Philippine Sea Plate.<br>From the spatial-temporal distribution, hypocenters of earthquakes were concentrated in a small region with a size of about 6 km by 12 km and occurred within a few days in December 2017 and January 2018, which could be classify as swarm activities from regular activities. Fault plane solutions of fast earthquakes except swarms, are dominant with a normal fault type mechanism. On the other hand, swarms had a small number of events with a normal fault type. The swarm activities started slightly later than the very low frequency earthquake (VLFE) activities. The regions of activity for the swarms and the VLFE seemed to generally overlap in consideration of the low spatial resolution of the VLFE locations.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><a href=\"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-content\/uploads\/sites\/2\/2025\/03\/image.png\"><img loading=\"lazy\" decoding=\"async\" width=\"1003\" height=\"365\" src=\"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-content\/uploads\/sites\/2\/2025\/03\/image.png\" alt=\"\" class=\"wp-image-6669\" \/><\/a><figcaption class=\"wp-element-caption\">Left: Comparison of the distribution of fast and slow earthquakes. Relocated hypocenters by this study are shown as colored dots. Black crosses represent tremors, and orange stars indicate very-low-frequency earthquakes.<br>Center and right: Triangle diagrams of focal mechanism results<\/figcaption><\/figure>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Ching-Yu Hu 1,2 , Masanao Shinohara 1 , Yusuke Yamashita 3 , Takashi Tonegawa 4 , Tomoaki Yamada 1,Takeshi Aku &hellip; <a href=\"https:\/\/www.eri.u-tokyo.ac.jp\/en\/research\/6668\/\" class=\"more-link\">Continue reading<span class=\"screen-reader-text\"> &#8220;Seismic activity around shallow plate boundary near westernmost Nankai Trough revealed by ocean bottom seismometer observation&#8221;<\/span><\/a><\/p>\n","protected":false},"author":9,"featured_media":6669,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[],"class_list":["post-6668","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research"],"_links":{"self":[{"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts\/6668"}],"collection":[{"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/users\/9"}],"replies":[{"embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/comments?post=6668"}],"version-history":[{"count":4,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts\/6668\/revisions"}],"predecessor-version":[{"id":6674,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts\/6668\/revisions\/6674"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/media\/6669"}],"wp:attachment":[{"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/media?parent=6668"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/categories?post=6668"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/tags?post=6668"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}