[S-SS25] 強震動・地震災害

[SSS25-P01] 東京都本郷での長周期地震動記録を用いた1931年西埼玉地震の震源モデルの推定

*中條 良亮¹、山中 浩明¹、地元 孝輔¹、工藤 一嘉²、纐纈 一起³、三宅 弘恵³ (1.東京工業大学大学院総合理工学研究科、2.日本大学生産工学部、3.東京大学地震研究所)

キーワード：1931年西埼玉地震、長周期地震動記録、震源深さ

The 1931 Nishi-Saitama earthquake occurred in the northwestern part of Saitama prefecture on September 21, 1931 with a magnitude of 6.9. This is one of the most destructive shallow crustal earthquakes in the Kanto district in the last 100 years. Heavy building damage was experienced in the epicentral area during the quake. It is important from the viewpoint of disaster mitigation to know the source model of the earthquake for considering ground shaking during future events. Abe (1974) estimated the focal depth according to observed P-wave travel time in distant station and suggested shallow focal depth. However, the focal depth has not been precisely understood.
In this study, we tried to estimate a source model of the 1931 Nishi-Saitama earthquake by comparing a long-period seismogram observed in Hongo, Tokyo, which is the only seismogram recorded completely in the Tokyo Metropolitan area with synthetic seismograms simulated by a 3D finite differential method considering recent detailed model of the Kanto basin. It is clarified that the main part of the observed long-period seismogram is composed of surface waves affected by the three-dimensional effect of the sedimentary layers in the Kanto basin. We also found good agreement between the calculated and observed seismograms, when the depth of the source fault is set to be in a range of 20-30 km with a rupture propagating from the bottom edge of the center of the fault.