Thermal Pressurization in Rough Faults: Implications for Frictional Melting and Rupture Dynamics

Abstract

Thermal pressurization (TP) is widely accepted as one of the primary dynamic frictional weakening mechanisms during earthquakes. However, most studies, whether experimental or numerical, have focused on the effects of TP on planar faults, while natural fault surfaces typically exhibit a fractal rough geometry. In this study, we numerically examine how roughness influences the fault thermal and mechanical evolution during coseismic slip. We control roughness using the root mean square prefactor $b_r$, testing faults with varying roughness levels, from a planar fault ($b_r$ = 0) to a rough fault ($b_r$ = 0.008), for two hydraulic diffusivities, representing intact (10⁻⁵ m²/s) and damaged (10⁻⁴ m²/s) rocks. Our findings indicate that the average temperature, shear stress drop, and effective normal stress are similar for rough and planar faults. However, while TP effectively buffers the average temperature rise, isolated patches of frictional melts form during coseismic slip at regions of high normal stress on rough faults, with their number and size increasing with $b_r$. For the rough faults, an increase in hydraulic diffusivity can lead to a transition from a crack to a pulse-like rupture style. Additionally, we investigate the effects of roughness on TP with different shear layer half-widths ($w$). We observe that faults with $w$ = 20 mm and $b_r$ = 0.008 do not generate sufficient heat for efficient TP in the early slip stages, leading to earthquake rupture arrest due to geometrical barriers.