[S-SS08] Fault Rheology and Earthquake Physics

[SSS08-20] Relative fluid pressure distribution around the 2000 Western Tottori Earthquake (M7.3) inferred from focal mechanism data of the aftershock

*Satoshi Matsumoto¹, Yoshihisa Iio², Shin'ichi Sakai³, Aitaro Kato⁴ (1.Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, 2.Disaster Prevention Research Institute, Kyoto University, 3.The University of Tokyo III/GSII, 4.Earthquake Research Institute, University of Tokyo)

Keywords:The 2000 Western Tottori Earthquake, Pore fluid pressure, aftershock activity

Aftershock activity following a large earthquake continues long time as expected to follow the modified Omori’s law even if no earthquake detected before occurrence of the mainshock. Aftershock sequence might be attributed to stress change by the large earthquake and strength weakening. Fluid pressure in the crust might create strength weakening and induces seismic activity as suggested by numerous studies, being one of the important parameters to consider not only aftershock sequence but also crustal evolution involving fault zone development. Here, we estimated relative fluid pressure distribution around hypocentral area of the 2000 Western Tottori Earthquake (M7.3). By using precise focal mechanism data obtained from seismic observation just after and 17 years the mainshock occurrence. Especially, “0.1 Manten” hyper dense seismic observation conducted in 2017 has successfully detected event with widely magnitude range. We estimated the relative fluid pressure from discrepancy of nodal plane geometry of the focal mechanism from optimal fault plane under regional stress condition. The result showed heterogeneous distribution of the relative fluid pressure field. High pressure part was found beside the large co-seismic slip area, which might indicate fluid injection to the fault (fault valve model) and sustain it for 17 years. On the other hand, the pressure decrease with distancing from fault plane, showing possibility that it behave under diffusion process. These results suggest a scenario of fault maturing process.