Characterizing deformation, damage parameters, and clay composition in fault zones: Insights from the Chelungpu Thrust, Taiwan, and Mozumi right lateral fault, Japan

The Chelungpu thrust fault, Taiwan, and the Mozumi right-lateral fault, Japan, provide an opportunity to characterize active faults in clastic sedimentary rocks and provide constraints to seismologic models. The northern Chelungpu fault has a 10-30 m wide primary damage zone characterized by dense fractures and chemical alteration. The southern Chelungpu fault has a 25-70 m wide primary damage zone characterized by dense fractures, alteration, intensely sheared rock, and secondary faults. The complexity of the damage zone, geochemistry, and clay mineralogy of the southern fault zone reflects its greater maturity (∼1 Ma) relative to the northern fault zone (∼46-100 Ka). A transition exists from smectite in exhumed fault core to illite-rich fault core at depth (200--1000 m) due to co-seismic fluid flow and radiated seismic energy. Clay composition plays a role in fault weakening.;Microstructures in deformed Mozumi siltstone indicate syn-tectonic fluid pressurization and flow, and shear concentrated in sericite-rich matrix. (Abstract shortened by UMI.).