Fault re-activation, stress interaction and rupture propagation of the 1981 Corinth earthquake sequence

By modelling vertical motions associated with the first two events of the 1981 Corinth sequence we show that both events produced surface rupture on the Perahora peninsula, moving in turn the Pisia and Alepohori faults. Motion on an offshore fault, suggested previously, did not occur in 1981, although the fault may have been responsible for the destructive 1928 Corinth event. The data used for the modelling are the most recent estimates of the seismic moments and stress drops of the earthquakes, together with a new information about coastal uplift and subsidence. Identification of the faults and their approximate coseismic slip distributions allows the Coulomb stress interaction between the events to be examined. At a depth of 6 km the rupture surface of the second event, which occurred 4 h after the first, was subject to a Coulomb stress increase of about 30% of its coseismic stress drop. The Coulomb stress on the rupture surface of the third event, which occurred 7 days later, was increased by a more modest 6% of its stress drop. The third event apparently propagated from east to west, consistent with the modelling, which suggests that the largest increase in Coulomb stress occurred at its eastern end. Although the offshore fault did not move in the earthquake sequence, it was bought more than 5 bars closer to failure by the 1981 earthquake sequence, so that future motion on it presents a potential hazard.