Seismic fault slip at depths simulated by high-velocity friction experiments under hydrothermal conditions

Seismic fault slip and rupture propagation often occur at crustal depths in the presence of hot and pressurized aqueous fluids (i.e., hydrothermal conditions). Previous experiments investigated fault frictional properties under hydrothermal conditions, but at imposed subseismic fault slip velocities (V ~μm/s). Here, using a rotary-shear apparatus equipped with a hydrothermal pressure vessel, we study friction at seismic slip velocities (V = 1.5 m/s) of gabbro- and marble-built faults under temperatures of 40 to 400 °C and pore water pressure of 30 MPa. We find that with increasing initial water temperature (Tamb), the dynamic friction during initial slip acceleration and subsequent high-velocity sliding decreases for both gabbro- and marble-built faults, while the slip-weakening distance decreases for gabbro but increases for marble. Then, during rapid deceleration at the end of sliding, frictional strength recovery decreases for gabbro with increasing Tamb and increases for marble independently of Tamb. As in previous experiments performed at room Tamb, the mechanical and microstructural data, plus numerical modeling, suggest that the seismic fault weakening mechanisms shift from flash heating to bulk melting for gabbro, and from flash heating to grain boundary sliding accommodated by diffusion creep for marble, with their activation processes depending on Tamb. Our results demonstrate the effects of ambient temperature on seismic fault friction, which contribute to changes in fault strength and dynamic weakening processes at crustal depths and should be considered in earthquake rupture modeling.