The 13 January 2001 El Salvador earthquake: A multidata analysis

On 13 January 2001, a large normal faulting intermediate depth event (Mw = 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 Greenʹs function analysis. In an attempt to discriminate between the two nodal planes (30° trenchward dipping and 60° 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 60° landward dipping nodal plane. We test the two possible fault models using regional broadband data and nearfield 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 × 50 km with an average slip of 3.5 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.