Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

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

[S-CG61] Dynamics in mobile belts

Mon. May 27, 2019 1:45 PM - 3:15 PM Convention Hall A (2F)

convener:Yukitoshi Fukahata(Disaster Prevention Research Institute, Kyoto University), Toru Takeshita(Department of Natural History Sciences, Graduate School of Science, Hokkaido University), Hikaru Iwamori(Geochemical Evolution Research Program, Japan Agency for Marine-Earth Science and Technology), Chairperson:Toru Takeshita, Kenta Kobayashi

2:15 PM - 2:30 PM

[SCG61-03] Non-double couple micro-earthquakes in the focal area of the 2000 Western Tottori earthquake (M7.3) by "0.1 manten" hyper dense seismic observation

*Yuto Hayashida1, Satoshi Matsumoto2, Yoshihisa Iio3, Shin'ichi Sakai4, Aitaro Kato4, Group for "0.1 Manten" hyper dense seismic observation Group registration (1.Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University, 2.Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, 3.Disater Prevention Research Institute, Kyoto University, 4.Earthquake Research Institute, the University of Tokyo)

Keywords:non-double couple earthquake, focal mechanism, the 2000 Western Tottori earthquake

Earthquakes with non-double couple (NDC) component could provide information such as geometric fault complexity, tensile failure, and fluid flow in faulting.

In this study, we found definite micro-earthquakes with NDC in the aftershock area of the 2000 Western Tottori earthquake (M 7.3) based on polarity analysis for first P-wave motion data from “0.1 manten” hyper dense seismic observation. The observation composed of a thousand seismic stations successfully provided with high resolution focal mechanisms of a lot of micro-earthquakes in the area.

We attempted to model the events with NDC by tensile-shear faulting, shear-tensile faulting, and multiple events with pure double couple focal mechanisms. We analyzed 8 events that distributes the entire after shock area.

Plausible models for the events occurring at shallower and deeper depth are the faulting with tensile crack and the multiple shear faulting models, respectively. The results suggest that fluid contributes to the crack opening at the shallow part. In contrast, fluid pressure does not sufficient to open tensile crack at the deep part. Therefore, the depth of the boundary may relate to the pressure of fluid at the earthquake fault. In addition, the events with large NDC component were located around co-seismic large slip area of the mainshock of the Western Tottori earthquake. This suggests that fluid exits around the co-seismic slip area.