Revealing the Contrast in Deformation Styles between Fault Core and Damage Zone throughout the Seismic Cycle(2/2)

Knowledge about fault deformation and its associated mechanism during the seismic cycle remains incomplete, due to the difficulty in deciphering the fault-zone rocks within fault core and damage zone, the consequence of both transient fault movement and long-term geomechanical response preserved in a fault. To this end, it is necessary to integrate geological evidence and laboratory work by which rocks were deformed, e.g., from slow to fast motion and from the slip plane to the surrounding host rock. By exploiting the current results of the Taiwan Chelungpu fault Drilling Project (TCDP) including well-documented seismically deformed materials within fault core and well-preserved borehole fault-zone cores, we focus on the topic of the contrast in deformation styles between the fault core and the damage zone throughout the seismic cycle through a group of interrelated sub-projects: (1) investigation of the transition in frictional properties of the fault-core material from coseismic to interseismic slip velocities, (2) examination of the bulk deformational behavior of damage-zone materials deformed at interseismic boundary conditions, and (3) measurement of the elastic stiffness of the damage-zone materials relevant to coseismic conditions. In particular, the sub-projects [2] and [3] derived from our concept was funded by NSF (1727661) for three years (Bulk rheology of fault damage zone materials and its implication for interseismic fault mechanics; Aug 1, 2017 to July 31, 2020). This field- and laboratory-based approach will likely (1) reconstruct a full spectrum of fault behavior during the seismic cycle, (2) reveal a new view of earthquake physics for a seismically active fault, and (3) expand our understanding of fault deformation together with significant applications to natural faults.