[S-CG52] Dynamics in mobile belts

[SCG52-P05] Spatial distribution and occurrence process of Non-Double-Coupled Earthquakes in the hypocentral region of the 2000 Western Tottori Earthquake using 0.1-manten seismic observations

*Takumi Motokoshi¹, Satoshi Matsumoto², Yoshihisa Iio³, Shinichi Sakai⁴, Aitaro Kato⁴ (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.Disaster Prevention Research Institute, Kyoto University, 4.Earthquake Research Institute, University of Tokyo)

Keywords:Non-double-couple earthquake

Non-double-couple (NDC) earthquake that is ordinary double couple (DC) faulting associated with additional faulting have been reported mainly in volcanic and geothermal regions. NDC component is considered to indicate the complexity of faulting and/or the presence of fluids. Detail analysis of NDC earthquakes are important for understanding the process of faulting and the mechanism of earthquake generation, and may provide opportunities to obtain new information about the stress and strength of the earth's crust.
Especially, specifying feature of the NDC event activity is valuable for our knowledge of earthquake process.
In this study, I showed characteristics of the NDC events found not in volcanic area but aftershock area of a large earthquake. Hyper-dense seismic stations covering the 2000 Western Tottori Earthquake (M7.3) aftershock area enable us detect precise focal mechanism of aftershock. I examined the spatial distribution of the NDC events and extracted the characteristics in detail by estimating optimal mechanisms from polarity data of first P wave arrivals.
As a result, I found that the detected earthquakes with magnitudes of 0.1 - 3 in the hypocentral region have NDC component of 10-20% in average, regardless of the magnitude and the location of the main shock fault and branch faults of the 2000 Western Tottori Earthquake. Spectra of NDC component seems to have high corner frequency compared with waves generated by shear faulting. This result suggests a possibility that smaller size tensile cracks than shear fault while propagating shear rupture.