Heterogeneous rupture on homogenous faults: Three‐dimensional spontaneous rupture simulations with thermal pressurization

Abstract

To understand role of fluid on earthquake rupture processes, we investigated effects of thermal pressurization on spatial variation of dynamic rupture by computing spontaneous rupture propagation on a rectangular fault. We found thermal pressurization can cause heterogeneity of rupture even on a fault of uniform properties. On drained faults, tractions drop linearly with increasing slip in the same way everywhere. However, by changing the drained condition to an undrained one, the slip‐weakening curves become non‐linear and depend on locations on faults with small shear zone thickness w, and the dynamic frictional stresses vary spatially and temporally. Consequently, the super‐shear transition fault length decreases for small w, and the final slip distribution can have some peaks regardless of w, especially on undrained faults. These effects should be taken into account of determining dynamic rupture parameters and modeling earthquake cycles when the presence of fluid is suggested in the source regions.

Spontaneous Dynamic Rupture Propagation beyond Fault Discontinuities: Effect of Thermal Pressurization

“…4). The effect of TP on fault 2 promotes the rupture triggered on fault 2, increasing its stress drop and making its slip-weakening curve nonlinear (Bizzarri and Cocco, 2006a, b;Urata et al, 2008). Therefore, the triggered rupture can quickly accelerate the propagation by itself.…”

“…Because the distance from the initial crack is longer at the fault side edge (x 6 km) than at the free surface (z 0 km), it is critically important to deep rupture jumping that the rupture speed in the x direction (in-plane direction) rapidly accelerate to a supershear velocity. When TP is in effect on a fault, a supershear rupture arises earlier than that arising in the case where TP is not in effect, not only because of the larger stress drop but also because of the nonlinearity of slip-weakening curves and the gradual decrease in the dynamic friction level (Urata et al, 2008). Therefore, the requirements on fault 1 for deep rupture jumping are (1) a large stress drop and (2) quick acceleration in the rupture propagation speed to supershear velocity.…”

“…Harris and Day (1993) showed that rupture jumps depend on whether or not the rupture speed exceeds the shear-wave velocity (i.e., supershear velocity). Under the effect of TP, the rupture velocity quickly achieves supershear velocity (Urata et al, 2008). Therefore, we chose parameters that cause supershear rupture even when TP is not in effect.…”

“…Numerical simulations suggested that TP can increase the breakdown stress drop (e.g., Andrews, 2002), slip-weakening distance (Noda and Shimamoto, 2005;Rice, 2006), peak slip rate, and rupture velocity (Bizzarri and Cocco, 2006a, b;Bizzarri and Spudich, 2008). Urata et al (2008) showed that TP changes the slip-weakening curves from place to place on a fault with a uniform coefficient of friction and stress.…”

Slip of a Two-degree-of-freedom Spring-slider Model in the Presence of Slip-dependent Friction and Viscosity

“…Several simple friction laws have been taken into account by some researchers, for examples, a velocity-dependent, weakening-hardening friction law [Burridge and Knopoff, 1967]; a purely nonlinearly velocity-weakening friction law [Carlson and Langer, 1989]; a piecewise, linearly velocity-dependent weakening-hardening friction law [Wang, 1995[Wang, , 1996[Wang, , 2012; a nonlinearly velocity-weakening friction law [Noda et al, 2009]; a displacement softening-hardening friction law [Cao and Aki, 1984/85]; and a piecewise, linearly slip-dependent friction law [Ionescu and Campillo, 1999;and Urata et al, 2008]. Cochard and Madariaga [1994] and Madariaga and Cochard [1994] assumed that purely velocity-dependent friction models can lead to unphysical phenomena or mathematically ill-posed problems.…”