The 2006 November,<i>M</i>_L= 5.0 earthquake near Lourdes (France): new evidence for NS extension across the Pyrenees

Abstract

A widely felt, ML = 5.0 earthquake occurred in the central French Pyrenees on 2006 November 17, close to the pilgrimage city of Lourdes, in a region where strong historical earthquakes produced severe damage and casualties in the 17th and 18th centuries. Seismic recordings performed by dense permanent networks and temporary stations allowed an exhaustive study of this event and its aftershock sequence, revealing a great coherency of all the parameters which characterize the rupture. More than 250 aftershock hypocentres, located in a 3-D tomographic model, are remarkably distributed on a 10 km2 quasi-planar surface which extends at depth between 6 and 10 km. This surface coincides with one of the main shock nodal planes, as inferred from P-wave polarities and body waveform modelling. The tectonic structure responsible for the earthquake is identified as an E–W oriented normal fault, dipping 56° north, a few kilometres south of the North Pyrenean Fault, recognized as the former boundary between the Iberian and Eurasian Plates. The mechanisms of the strongest aftershocks are also clearly extensional (Tables 1 and 2). Table 1.Open in new tabDownload slideFocal solution parameters for the main shock, the seven strongest aftershocks, the 2006 December 16 and the 2007 November 15 events.Table 2.Open in new tabDownload slideSource parameters obtained from body waveform modelling, with their uncertainties, for the main shock, the three strongest aftershocks, and the December 16 event.