著者

小山 順二 都筑 基博

出版者

北海道大学大学院理学研究院

雑誌

北海道大学地球物理学研究報告 (ISSN:04393503)

巻号頁・発行日

vol.76, pp.87-96, 2013-03-19

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After the 2011 Tohoku-oki megathrust earthquake, we have proposed a hypothesis on the earthquake activity characterizing the distribution of earthquakes into Along-dip Double Segmentation (ADDS) and Along-strike Single Segmentation (ASSS): The apparent absence of earthquakes in the trench-ward segments as opposed to the Japan Island-ward segments that generate repeated smaller earthquakes (ADDS), where the 2011 Tohoku-oki megathrust occurred. In the mean time, a young and buoyant plate is subducting rapidly under the overriding plate where there is weak seismic activity before the main event all over the plate interface of the subduction zone (ASSS). The 1960 and 2010 Chile megathrusts occurred in ASSS. In and near Japan, ADDS earthquake activity is restrictively found along the Pacific side of Hokkaido and Tohoku regions and the Hyuganada, Kyushu. The rest of seismic activity near Japan is classified into ASSS. We found a distinct difference in tsunami excitations between earthquakes in ADDS and ASSS, comparing tsunami magnitude m from local tsunami heights and seismic moment Mo from long-period surface-waves. Tsunami wave heights of ASSS earthquakes are almost two times larger than those of ADDS's. This is also confirmed by studying tsunami magnitude Mt calculated from teleseismic tsunami wave heights. The reason of this different excitation of tsunamis is also considered.