Directivity Detection and Source Properties of the 11 May 2011 Mw 5.2 Lorca, Spain, Earthquake

Abstract

A kinematic finite‐source study of the 11 May 2011 M w 5.2 Lorca, Spain, earthquake has been performed using broadband data from the Spanish National Network. The nodal plane ambiguity of the double‐couple solution was resolved from finite‐source analysis, and a rupture velocity of 1.8 km s−1 and the northeast–southwest‐striking northwest‐dipping plane was found to best fit the data. This fault plane corresponds to the central sector of the Alhama de Murcia fault (AMF). The resulting slip distribution has a maximum of 19.3 cm and a total seismic moment of 6.25×1016 N·m. A Jackknife test has been performed to estimate the fault plane errors and their consequences in the slip distribution. Also synthetic tests have been performed to evaluate the errors in the finite‐source modeling. From this model, a prediction of the strong ground motion near the fault, corrected for soil amplification, is given in terms of peak ground velocity (PGV), which fits with the observed value at the accelerograph in the city of Lorca. We also compared the PGV converted to modified Mercalli intensity at the surface with the intensity distribution, also showing good agreement. Finally we extracted the directivity pulse from the strong ground motion record at Lorca with 0.5 s period in the transverse component to the AMF direction and 33 cm s−1 PGV. To further analyze the directivity effect, we estimate the duration and azimuthal amplitude distribution of the source time functions, finding them to be shorter and of greater amplitude in the direction of rupture and longer and smaller in amplitude in the opposite direction.