Foreshocks and pre‐events associated with the nucleation of large earthquakes

We propose a theoretical model which can explain the occurrence of foreshocks and pre‐events associated with the nucleation of large earthquakes. We consider a broad weak zone with a locally strong part (asperity) on a fault plane in a two‐dimensional framework and examine the transition process from quasistatic nucleation to high‐speed rupture propagation through numerical simulations. The dynamic rupture of the asperity occurs in three different manners, as aseismic slip, foreshock or pre‐event, depending on the peak stress of the asperity. In all cases the rupture of the asperity accelerates the nucleation of main rupture.