Japan Geoscience Union Meeting 2014

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Symbol S (Solid Earth Sciences) » S-SS Seismology

[S-SS30_28AM1] New perspective of great earthquakes along subduction zones

Mon. Apr 28, 2014 9:30 AM - 10:45 AM Main Hall (1F)

Convener:*Kyuichi Kanagawa(Graduate School of Science, Chiba University), Takashi Furumura(Center for Integrated Disaster Information Research (CIDIR) Interfaculty Initiative in Information Studies, The University of Tokyo), Shuichi Kodaira(Institute for Research on Earth Evolution Japan Agency for Marine-Earth Science and Technology), Masanobu Shishikura(Active Fault and Earthquake Research Center, GSJ/AIST), Chair:Takashi Furumura(Center for Integrated Disaster Information Research (CIDIR) Interfaculty Initiative in Information Studies, The University of Tokyo)

9:30 AM - 9:45 AM

[SSS30-01] Long-term seismic quiescence and activation anomalies preceding to the 2004 Sumatra and the 2005 Nias earthquakes

*Kei KATSUMATA1 (1.Inst. Seismology and Volcanology, Hokkaido University)

Keywords:The 2004 Sumatra earthquake, The 2005 Nias earthquake, seismic quiescence, seismic activation, ZMAP, ISC

I find long-term precursory seismic quiescence and activation anomalies before the 2004 Sumatra (Mw9.1) and the 2005 Nias (Mw8.6) earthquakes. An earthquake catalog created by International Seismological Center is analyzed between 1964 and 2004, including 1153 earthquakes shallower than 100 km with the body wave magnitude of 5.0 ≤ M ≤ 6.0. A detailed analysis of the earthquake catalog using a gridding technique (ZMAP) shows that the 2004 Sumatra and the 2005 Nias earthquakes are preceded by not only a seismic quiescence anomaly started in December 1987, but also a seismic activation anomaly started in July 1989. The quiescence and activation areas are located very closely each other between 2S and 6N, which cover the area around the rupture initiation point of the 2004 Sumatra earthquake and the whole area ruptured by the 2005 Nias earthquake. The observed spatial pattern of quiescence and activation can be explained by stress perturbation due to a long-term slow slip event located on the two main shock faults, which is predicted by a numerical simulation [Kato et al., 1997].Kato, N., M. Ohtake, and T. Hirasawa (1997), Possible mechanism of precursory seismic quiescence: Regional stress relaxation due to preseismic sliding, Pure Appl. Geophys., 150, 249-267.