A possible rupture process of slow earthquakes on a frictional fault

Abstract

A possible mechanism for the occurrence of slow earthquakes is investigated by calculating numerical solutions for the dynamical rupture process on a quasi-three-dimensional fault with heterogeneous frictional strengths. Experimental friction laws for the dependence of sliding frictional stress on slip velocity, which are based on the cohesive properties of fault asperities, are taken into considerations. It is found that the applied stress does not drop very rapidly with time and the rupture velocity remarkably decreases as the dependence on slip-velocity becomes smaller. These deceleration effects for the rupture propagation are greatly enhanced with increasing heterogeneities in the distribution of frictional strength and as the initial shear stress has lower levels with respect to the average strength. For these cases, the growth of rupture is extremely slow in a nucleus region with the dimension as large as 10 times the initial rupture length, and gains a terminal velocity dependent on the above factors. The displacement-time function becomes noticeably extended in these cases, and indicates a stick—slip-like phenomena in the extended time interval for a strongly heterogeneous fault. It seems that these results could explain the characteristic features of slow earthquakes.