Tectonic interpretation of the source of the 2011 Mw 5.2 Lorca earthquake and its surface effects

Abstract

On 11 May 2011 a 5.2 Mw earthquake struck the city of Lorca (south-east Spain), causing huge damage. The aim of this paper is to analyse and interpret the geological source of the earthquake in order to explain its location, size and surface effects. We have studied in detail the tectonic structure of the epicentral region, the spatial distribution of the seismic sequence and the distribution and characteristics of the damage and earthquake-triggered debris and rock falls. Combining all this information we provide a synoptic view of the genesis and the effects of the earthquake and discuss the implications of this event in the context of the seismic hazard of the adjacent Alhama de Murcia fault (FAM) segments according to Coulomb failure stress modelling. The seismotectonic characteristics of the earthquake, the local structure of the epicentral area, and the location and amount of surface deformation are consistent with the asymmetric (southward propagating) rupture of a section of the FAM up to 7 km in length. Nevertheless, most of the energy was released in a complex structure coinciding with the Matalauva duplex located to the SW of the hypocentre. This rupture produced a pulse of NW-SE strong ground motion (normal to the FAM), with its maximum amplitude located to the south-west of the seismic sequence. This explains the directionality effects observed in the distribution of the rock-falls and building damage. The concentration of the worst of the damage on the northern slopes of the Sierra de la Peña Rubia is consistent with this seismotectonic scenario.