Rupture directivity of the 2011, Mw 5.2 Lorca earthquake (Spain)

Abstract

On May 11th 2011, a rather small earthquake caused nine fatalities in the city of Lorca, SE‐Spain. We analyze seismograms from a dense network to characterize the source of this earthquake. We estimate an oblique reverse faulting mechanism, moment magnitude of 5.2 and a shallow hypocenter (4.6 km), at only 5.5 km epicentral distance from the city center. Double difference relocations yield a ∼5 km long, NE‐SW trending distribution of aftershocks SW of the mainshock, suggesting a SW propagating rupture along the Alhama de Murcia fault. We use the Mw 4.6 foreshock and an Mw 3.9 aftershock as empirical Greens functions to estimate apparent source time functions, observing a clear directivity effect. We model apparent durations with a unilateral and asymmetric bilateral rupture, in both cases obtaining rupture directivity of ∼N220°E, towards Lorca. In addition to the near epicenter and shallow depth, directivity may have contributed to the significant impact.