Dynamic modeling of slow earthquakes based on thermoporoelastic effects and inelastic generation of pores

We numerically simulate features of slow earthquakes to understand their generation mechanism in the framework of dynamic modeling. Their typical features will be that the fault rupture velocity and stress drop are markedly lower than those of ordinary earthquakes. We assume a fault in a thermoporoelastic medium taking account of fluid flow and inelastic creation of pores on the fault. This paper is an extension of our studies published in the work of Suzuki and Yamashita (2006, 2007, 2008), in which a nondimensional parameter S-u was shown to play a critical role in dynamic fault rupture. The parameter S-u represents the dominance of the effect of inelastic pore creation over that of frictional heating under the condition of no fluid flow. However, it can be shown that S-u plays an important role even if the fluid flow is considered. In the present study we successfully simulate slow fault rupture growth and low stress drop, which characterize the slow earthquakes. Critical ingredients of our modeling are assumptions of (1) S-u considerably larger than assumed for the simulation of ordinary earthquakes, (2) fluid flow into the inelastically created pores, and (3) initial shear stress significantly smaller than assumed for the simulation of ordinary earthquakes. The assumption of a large value of S-u corresponds to that of a slip-resistant and low-stress-drop zone. The fluid inflow can promote the fault rupture in the slip-resistant zone.