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 can show that both events produced surface rupture on the Perachora
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 co-seismic 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 2 hours after the first, was subject to a Coulomb
stress increase of about 30% of its co-seismic stress drop. The Coulomb stress on the
rupture surface of the third event, which occurred seven 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 close to failure by the 1981
earthquake sequence, so that future motion on it presents a potential hazard.