The 13 January 2001 El Salvador earthquake:: A multidata analysis -: art. no. 2203

[1] On 13 January 2001, a large normal faulting intermediate depth event (M-w = 7.7) occurred 40 km off the El Salvadorian coast ( Central America). We analyze this earthquake using teleseismic, regional, and local data. We first build a kinematic source model by simultaneously inverting P and SH displacement waveforms and source time functions derived from surface waves using an empirical Green's function analysis. In an attempt to discriminate between the two nodal planes (30degrees trenchward dipping and 60degrees landward dipping), we perform identical inversions using both possible fault planes. After relocating the hypocentral depth at 54 km, we retrieve the kinematic features of the rupture using a combination of the Neighborhood algorithm of Sambridge [ 1999] and the Simplex method allowing for variable rupture velocity and slip. We find updip rupture propagation yielding a centroid depth around 47 km for both assumed fault planes with a larger variance reduction obtained using the 60degrees landward dipping nodal plane. We test the two possible fault models using regional broadband data and near-field accelerograms provided by Universidad Centro Americana [ 2001]. Near-field data confirm that the steeper landward dipping nodal plane is preferred. Rupture propagated mostly updip and to the northwest, resulting in a main moment release zone of approximately 25 km x 50 km with an average slip of similar to3.5 m. The large slip occurs near the interplate interface at a location where the slab steepens dip significantly. The occurrence of this event is well-explained by bending of the subducting plate.