Seismic source directivity on May 11, 2011 Lorca earthquake

Abstract

The seismic source study performed to the Lorca 11 May 2011, 5.1 Mw earthquake allow us to conclude that a directivity effect is responsible of much of the high acceleration recorded at the city of Lorca which causes great damage. A new moment seismic tensor inversion has been obtained for the three main events of the earthquake series associated to the Alhama de Murcia Fault. A slip distribution over the fault plane has been obtained, showing a unilateral rupture in hypocenter-Lorca direction with a rupture velocity of 2.4 km/s with a maximum displacement of 17.5 cm at 2 km depth. The source time function analysis performed though Empirical Green Functions and the Wood-Anderson Amplitudes relation between main event and lower magnitude aftershocks shows also a clear directivity effect in the fault direction. A directivity pulse has been extracted from the strong ground motion instrument at Lorca of 33.2 cm/s centered at a 1.5 Hz which we considered main responsible of the earthquake damage.