[S-CG45] Science of slow-to-fast earthquakes

[SCG45-39] Simulation of thermo-hydro-mechanical evolution of fault gouges deformed at seismic slip velocities

*Ching-En Kung¹, Chia-wei Kuo², Li-wei Kuo^1,3, Thi Trinh Nguyen¹, Szu-ting Kuo¹ (1.Department of Earth Science, National Central University (NCU), Taoyuan, Taiwan, 2.Science and Technology Research Institute for DE-Carbonization (STRIDE-C), National Taiwan University, Taipei, Taiwan, 3.Earthquake-Disaster & Risk Evaluation and Management Center, NCU)

Keywords:Frictional strength, Rotary shear, Water-saturated gouge, Simulation

Catastrophic events such as earthquakes, tsunamis, and landslides are often associated with large coseismic slips localized in relatively thin slip zones. Therefore, understanding the strength and frictional behavior of slip zones, and the associated deformation mechanisms, is crucial for earthquake physics and seismic hazard assessment. Water-saturated, clay-rich gouges are common components of fault slip zones at shallow crustal depths. The frictional properties of water-saturated clay-rich gouges have been experimentally investigated by rotary shear-type experimental assemblies. Here, to understand physicochemical processes within the gouge layer during seismic slip, we use a comprehensive simulator, THMC2D (Thermal-Hydraulic-Mechanic-Chemical Processes, developed by CAMRDA at NCU), that couples fluid flow, hydrologic transport, heat transfer in two dimensions. Mechanical data show that under both fluid undrained and drained conditions, the apparent coefficient of friction (the ratio of shear stress to normal stress), μ, increased to a peak value of ~0.4, followed by a dramatic weakening with increasing displacement to a steady state value of 0.2. In particular, in the drained condition, μ shows a re-strengthening with increasing displacement after reaching the steady state. Simulation results show that (1) a rapid increase in pore pressure is responsible for the observed frictional weakening, and (2) high temperature is responsible for the thermal decomposition of the clay minerals. This model can help us better comprehend the frictional processes within fault gouges during experiments.