Source functions of a two-asperity fault model

A fault made of two coplanar asperities subject to a constant strain rate is considered. The fault is modelled as a discrete dynamical system made of two blocks coupled by a spring and pulled at constant velocity on a rough plane. Such a system exhibits a variety of slipping modes, including the slip of single asperities and the simultaneous slip of both asperities. The associated source function can be expressed by the seismic moment rate as a function of time. The moment rate depends on the state of the system preceding the earthquake, which can be described by a single variable expressing the difference between the stresses imposed to the two asperities. We present a systematic study of the moment rate as a function of this variable and show how the moment rate changes as a function of the model parameters. The observed source function of the 2010 Maule (Chile) earthquake, that was the result of the failure of two main asperities, is interpreted in the framework of the proposed model.