11:15 AM - 11:30 AM
[SCG62-08] Fault rocks and paleostress fields in the San-in shear zone
Keywords:fault rocks, The 2000 Western Tottori earthquake, Paleostress analysis
Recent geologic study around aftershock area of the 2000 Western Tottori earthquake revealed that the distribution of faults around aftershock area was concordant with the aftershock distribution and explained the relation between the geometry of the source fault and inactive fault.
In this study, We estimated paleostress fields formed inactive fault in granitic rocks around aftershock area by the Hough-transform-based stress tensor inversion method (Yamaji et al., 2006; Sato and Yamaji, 2006). First, I estimated paleostress fields of each faults having fault gouge or cataclasite as characters of fault rocks. As the result, two stress tensors were detected with strike-slip faulting regimes from faults having fault gouge. One is E-W trending σ1-axis and N-S trending σ3-axis, the other is N-S trending σ1-axis and E-W trending σ3-axis. The former is roughly consistent with the present stress field in SW Japan. On the other hand, three stress tensors were detected with reverse and normal faulting regimes from faults having cataclasite.
With respect to different paleostress fields, fault system around aftershock area was formed by stress fields with reverse and normal faulting regimes in the past seismogenic zone and by stress fields with strike-slip faulting regimes in shallow depth with low confining pressure.