{"id":2899,"date":"2020-07-02T14:58:58","date_gmt":"2020-07-02T05:58:58","guid":{"rendered":"http:\/\/www.eri.u-tokyo.ac.jp\/en\/?p=2899"},"modified":"2020-07-02T15:00:44","modified_gmt":"2020-07-02T06:00:44","slug":"stress-loading-and-the-occurrence-of-normal-type-earthquakes-under-boso-peninsula-japan","status":"publish","type":"post","link":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/research\/2899\/","title":{"rendered":"Stress loading and the occurrence of normal-type earthquakes under Boso Peninsula, Japan"},"content":{"rendered":"\n<p style=\"text-align:center\">Akinori Hashima<sup>1<\/sup>, Hiroshi Sato<sup>1<\/sup>, and\nToshinori Sato<sup>2<\/sup><\/p>\n\n\n\n<p style=\"text-align:center\"><sup>2<\/sup>Earthquake Research Institute,\nUniversity of Tokyo, <sup>2<\/sup>Graduate School of Science, Chiba University<\/p>\n\n\n\n<p style=\"text-align:center\">Earth, Planets and Space, 72, 79, https:\/\/doi.org\/10.1186\/s40623-020-01201-6   Published: 3 June 2020 <\/p>\n\n\n\n<p>Boso Peninsula, Japan, was formed by\nthe interaction of the Philippine Sea, Eurasian and Pacific plates around the\ntrench\u2013trench\u2013trench Boso triple junction. Normal-type earthquakes are\npersistently observed in the subducting Philippine Sea slab under the peninsula\nat a depth of\u2009~\u200930&nbsp;km, including a recent (2019)&nbsp;<em>M<\/em><sub>w<\/sub>&nbsp;4.9\nearthquake which caused shaking throughout the Kanto region (greater Tokyo).\nSuch shallow intraplate earthquakes are potentially hazardous to this heavily\npopulated region, yet their mechanism is poorly understood, especially in the\ncontext of a three-plate system. Here, we calculate stress rates in the\nPhilippine Sea slab and the surrounding area, using a subduction model\nconstructed in a previous study, to explain the generation of the regional\nstress field and its effect on earthquake occurrence. In general, the\ncalculated stress rates under Boso Peninsula are horizontally extensional both\nabove and below the Eurasian\u2013Philippine Sea plate interface. We apply our\ncalculated stress rates to the nodal planes of the observed earthquakes to\ncalculate the Coulomb failure function (\u0394CFF). These calculated \u0394CFFs are\ngenerally positive on normal-type earthquakes under Boso. The \u0394CFFs are also\nconsistent with earthquakes in adjacent areas that are seismically active, for\nexample, in the Philippine Sea plate to the south, in the collision zone around\nIzu Peninsula, and in the cluster in the Eurasian plate northeast of Boso\nPeninsula, which further supports our stress loading model. Calculation of the\nindividual contributions of Philippine Sea plate and Pacific plate subduction\nshows that the development of the stress field around Boso is dependent upon\ncontributions from both subducting plates. In contrast, the arc\u2013arc collision\nat Izu Peninsula has little influence.<\/p>\n\n\n\n<p>\n\nFigure Caption (a) Landforms around Boso Peninsula (BP) and the Kanto Basin (KB). Solid contours map upper surface of PHS plate, and dashed contours, upper surface of PAC plate. Focal mechanism marks location of&nbsp;<em>M<\/em><sub>w<\/sub>&nbsp;4.9 normal-type earthquake of 2019\/05\/25. Inset: Schematic illustration of internal structure and slip distribution of our model in vertical section perpendicular to the trench. (b) Focal mechanisms for earthquakes distributed in PHS plate, from 2003\/1\/1 to 2019\/9\/30. Focal mechanisms are colored with respect to \u0394CFF. Distribution of earthquakes with positive (+) and negative (\u2212) \u0394CFF shown in histograms. \n\n<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Akinori Hashima1, Hiroshi Sato1, and Toshinori Sato2 2Earthquake Research Institute, University of Tokyo, 2Gra &hellip; <a href=\"https:\/\/www.eri.u-tokyo.ac.jp\/en\/research\/2899\/\" class=\"more-link\">Continue reading<span class=\"screen-reader-text\"> &#8220;Stress loading and the occurrence of normal-type earthquakes under Boso Peninsula, Japan&#8221;<\/span><\/a><\/p>\n","protected":false},"author":9,"featured_media":2900,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[],"class_list":["post-2899","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\/2899"}],"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=2899"}],"version-history":[{"count":2,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts\/2899\/revisions"}],"predecessor-version":[{"id":2902,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts\/2899\/revisions\/2902"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/media\/2900"}],"wp:attachment":[{"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/media?parent=2899"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/categories?post=2899"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/tags?post=2899"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}