Spontaneous processes for nucleation, dynamic propagation, and stop of earthquake rupture

Abstract

We developed a model which can naturally explain the entire process of nucleation, dynamic propagation, and stop of earthquake rupture. In this model we represent frictional interaction between fault surfaces by a slip‐dependent constitutive relation, and use it as the fundamental law governing the entire process of earthquake rupture. We considered a broad weak zone with a locally strong part (asperity) on a fault plane and examined the entire rupture process proceeding with the increase of external shear stress through numerical simulations. The nucleation process first proceeds quasi‐statically at the weakest portion with the increase of external stress and brings about high stress concentration at the asperity. Then dynamic rupture starts at the asperity, but this dynamic rupture is arrested soon. After the arrest of the local dynamic rupture, the quasi‐static nucleation process proceeds again and brings about high stress concentration at both ends of the weak zone. When the stress concentration reaches a critical level, dynamic rupture starts at the endzones and propagates outward. The rupture propagation is gradually accelerated to S‐wave velocity until it reaches much stronger parts (barriers). The dynamic rupture is decelerated and finally arrested, with it propagating into the barrier. Our model successfully describes the transition process from nucleation to dynamic rupture propagation observed in laboratory experiments of stick‐slip.