SUPERFICIAL SIMPLICITY OF THE 2010 MW 7.2 EL MAYOR-CUCAPAH EARTHQUAKE OF BAJA CALIFORNIA

Major earthquakes can have moment tensors that differ significantly from predictions based on a single planar elastic shear-dislocation. A recent example is the 2010 El Mayor-Cucapah earthquake which ruptured a 120 km straight fault trace, extending the Elsinore-Laguna Salada fault system to the Gulf of California. The sequence was initiated about 15 s prior to the main fault rupture by a moderate normal event along a pull-apart-basin. Although the surface trace is nearly linear, the event involved fault segments with >5 km jogs at depth where the rupture found its way through a complex set of preexisting normal and strike-slip fault segments including undiscovered faults beneath the Colorado River Delta. The inferred complexity of the subsurface fault geometry and the distribution of slip orientation accounts for the large non-double-couple component of the moment tensor.