2:45 PM - 3:00 PM
[SSS06-05] Microfabric analysis of damaged zone of principal shear zone in the frontal megathrust in the Nankai Trough
Keywords:Nankai trough, frontal thrust, principal shear zone, slow slip, fault fabric, tsunamigenic fault
The underlying micro-mechanical processes responsible for the fast or slow slips are, however, poorly known.
We revisited the recovered core sample of the frontal thrust and added further micro-textural observations for damaged zone to already reported principal shear zone. The detailed mineralogical, chemical and micro fabric analysis for a principal shear zone presents the nearly complete transformation from smectite to illite, which is consistent with frictional heating. The observed micro-texture of the gouge and its surroundings of damaged zone is characteristic of experimentally-produced brittle textures for slow slip. This suggests an overprint of slow slip on the previous seismo-tsunamigenic fast slip. This micro-tectonic based interpretation is consistent with the recent observation of inter-sesimic slow slip beneath the outer wedge and around the frontal megathrust. We suggest that the illite-smectite lithology of gouge and surrounding is conditionally stable, allowing it to transition from co-seismic rapid slip to inter-seismic slow slip at different times.