著者

前田 宜浩 笠原 稔

出版者

北海道大学大学院理学研究院自然史科学部門(地球物理学) = Department of Natural History Sciences (Geophysics), Graduate School of Science, Hokkaido University

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.72, pp.219-230, 2009-03-15

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On August 2, 2007, a shallow crustal earthquake occurred at west off Sakhalin Island, far eastern Russia. Moment magnitude (MW) of this earthquake determined by Global CMT is 6.2. This earthquake generated severe damage to habitants and buildings at Nevelsk city near the epicenter. Visible large uplift was reported along the coast, and tsunami was observed even though its small magnitude. Teleseismic broadband waveforms from IRIS show long-duration P-wave pulse; the duration is comparable to that of MW 6.8 event. Teleseismic data also show later phases at some stations. Seismic source model is estimated using teleseismic data by applying the waveform inversion method. The estimated source model is compared with those from two earthquakes occurring in Sakhalin. The 2007 event is characterized by the slow slip event. Spectral ratio based on broadband strong-motion data between the 2007 event and MW 5.6 event shows that smaller excitation of short-period seismic waves by the 2007 event than the MW 5.6 event. This feature is also confirmed by the analysis of teleseismic waveforms. Theoretical source spectral ratio based on the ω^[-2] source model using source parameters estimated from the waveform inversion well explains the observed spectral ratio. Seismic moment derived from waveform inversion is smaller than those derived from the crustal deformation and tsunami data. An aseismic slip is considered as a possible cause of this discrepancy.