Japan Geoscience Union Meeting 2018

Presentation information

[EJ] Oral

S (Solid Earth Sciences) » S-CG Complex & General

[S-CG57] Dynamics in mobile belts

Tue. May 22, 2018 1:45 PM - 3:15 PM A05 (Tokyo Bay Makuhari Hall)

convener:Yukitoshi Fukahata(Disaster Prevention Research Institute, Kyoto University), Toru Takeshita(Department of Natural History Sciences, Graduate School of Science, Hokkaido University), Hikaru Iwamori(海洋研究開発機構・地球内部物質循環研究分野), Chairperson:Iwata Takaki, Shibazaki Bunichiro

1:45 PM - 2:00 PM

[SCG57-01] "0.1 Manten" hyper dense seismic observation for a sight of crustal activity –preliminary result about focal mechanisms around source fault hosting the 2000 Western Tottori EQ (M7.3) –

★Invited Papers

*Satoshi Matsumoto1, Yoshihisa Iio2, Shin'ichi Sakai3, Aitaro Kato3, Yuto Hayashida4, Group for "0.1 Manten" hyper dense seismic observation (1.Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, 2.Disaster Prevention Research Institute, Kyote University, 3.Earthquake Research Institute, University of Tokyo, 4.Graduate School of Science, Kyushu University)

Keywords:focal mechanism, stress field, "0.1 Manten" hyper dense seismic observaiton

Weakening process of the crust is an important key for understanding of crustal dynamics. Earthquake faulting is a phenomenon of inelastic deformation taking place within seismogenic zone and its occurrence is affected by stress condition of the crust. Non-uniform co-seismic slip on the large earthquake faulting produces a spatially heterogeneous stress field around the fault. Therefore, a response of stress field to stress perturbation induced by large earthquake occurrence is important and provides a new insight toward crustal strength.
High-resolution focal mechanisms for small earthquakes illuminate stress field in detail. The accuracy of focal mechanism estimation strongly depends on coverage of station above a hypocenter. Therefore, we have developed a new seismic observation system for long-term recording and deployed one thousand stations in an aftershock area of the 2000 Western Tottori earthquake (M7.3). Through this dense seismic network, an accuracy in focal mechanism solution is expected to be smaller than five degrees. Earthquakes with magnitude greater than 2.0 occurred at the center of the network have been detected. The focal mechanisms were determined with accuracy less than a few degrees. These solutions showed the earthquakes were not always pure double couple source radiation pattern, suggesting fault of the small earthquake non-uniform slipped as large earthquake. The high accuracy fault plane solution has a great potential to expose long-term weakening process of the crust and might be discussed from comparison with a detailed mapping of minor faults/fractures by geological studies.