How Frictional Properties Lead to Either Rupture-Front Focusing or Cracklike Behavior

Abstract

Abstract A numerical simulation of the stress concentration and earthquake rupture process of a circular asperity is performed using a laboratory-derived rate- and state-dependent friction law. The asperity is locked during an interseismic period, and it is surrounded by regions of stable sliding. This situation is thought to be common at plate interfaces with relatively low seismic coupling. Aseismic sliding penetrates into the asperity, and the distance of its penetration depends on frictional properties. Shear stress is concentrated in the boundary regions between the locked and stable sliding regions before earthquake occurrence, and this stress distribution affects the earthquake rupture process. When aseismic sliding propagates little into the asperity, rupture propagates faster in the stress concentrated region, and rupture fronts propagating clockwise and counterclockwise around the asperity meet at an end of the asperity opposite to the rupture initiation point. This rupture-front focusing produces high slip rates in the final stage of asperity rupture, which is consistent with observations of short-period seismic waves radiated from some large interplate earthquakes. On the other hand, when the distance that aseismic sliding propagates into the asperity is long, rupture starts near the center of the asperity and propagates outward like an expanding crack, generating no rupture-front focusing.