Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

Fig. 4: a) Development of S-C fabric on a phyllosilicate-rich gouge (sample MF15) at 300 µm/s. b) Development of Y-B- P-R fabrics on a granular mineral-rich gouge (sample MF14) at 10 µm/s. c) Distributed deformation at slip velocity of 18 mm/s in a phyllosilicate-rich gouge (sample PPF10). D) Micrometric localized deformation developed in phyllosilicate-rich gouge at a shear velocity of 1 m/s (sample PPF12). The microstructures suggest that in a fault reactivation process, deformation begins ductilely by developing phyllosilicate foliation and grain size reduction in millimetric bands (Fig 4.C) at velocities of up to ~20 mm/s. Under dynamic conditions, from ~20 mm/s to 1 m/s in our experiments, deformation localizes in micrometric PSZs characterized by intense grain size reduction, sub-rounded granular minerals, cataclasis, and low-angle foliation operating brittle deformationmechanisms. This suggests that the propagation of earthquakes in upper plate faults during the post- seismic stage begins with ductile deformation accommodated mainly by phyllosilicates and culminates in brittle deformation induced by normal stress reduction driven by post-seismic relaxation.