The 13 January 2001 El Salvador earthquake: A multidata analysis

Abstract

[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 (30°trenchward dipping and 60°l andward 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 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  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 wellexplained by bending of the subducting plate.

Triggering of destructive earthquakes in El Salvador

“…The fault has a rupture area of 2532 km 2 (60 ϫ 42 km). By using teleseismic, regional, and local data, Vallée and Bouchon (2003) modeled this rupture area and obtained a plane with the same orientation. For the crustal earthquake of 13 February the best-fit solution indicates a rupture sized 471 km 2 (40 ϫ 12) striking N94ЊE and dipping 70ЊS (Fig.…”

Fault kinematics in northern Central America and coupling along the subduction interface of the Cocos Plate, from GPS data in Chiapas (Mexico), Guatemala and El Salvador

“…Topography and bathymetry are from Shuttle Radar Topography Mission (Farr & Kobrick 2000) and Smith & Sandwell (1997), respectively. Plate velocities relative to Caribbean Plate are from Nuvel1 (DeMets et al 1990) for Cocos Plate, DeMets et al (2000) for North America Plate and Weber et al (2001) for South America Plate.…”

Upper lithospheric structure of the subduction zone offshore of southern Arauco peninsula, Chile, at ∼38°S

“…At the trench–outer rise area, the oceanic crust is pervasively fractured and hydrated by extensional bending‐related faults, allowing the percolation of fluids to mantle depths and thus resulting in the weakening of the oceanic lithosphere prior to subduction [ Ranero et al , 2003]. During subduction, large intraplate earthquakes associated with normal faulting under the inner trench slope region suggest that plate bending and faulting continues until the plate unbends at greater depth [ Mikumo et al , 2002; Vallée et al , 2003]. Thus oceanic lithosphere already hydrated and weakened at the outer rise is further fractured and faulted by extensional stresses underneath the overriding plate.…”