Density-depth model of the continental wedge at the maximum slip segment of the Maule Mw8.8 megathrust earthquake

Abstract

Complexities in the rupture process during a megathrust earthquake can be attributed to the combined effect of inhomogeneous distribution of stress accumulated during the interseismic period and inho-mogeneous rheology of the seismogenic contact. We modeled the free-air gravity field of the southern Central Chile convergent margin along five 2-D profiles that cross the patch of highest slip during the Chilean 2010 megathrust earthquake in order to analyze variability in the density and shape of the con-tinental wedge and its relationship withseismotectonics. We also analyzed the bathymetry to derive the long-term interplate friction coefficient. The results show that the high slip patch during the Maule earthquake corresponds to a segment of the margin characterized by (1) low densities in the continen-tal wedge, (2)low vertical loading over the inter-plate contact, (3) a well-developed shelf basin and, (4)low taper angles consistent with a low effective basal friction coefficient. We interpret the correla-tion between these parameters in terms of the total potential energy change during the earthquake and conclude that if the normal stress or frictional coefficient are low, then a large slip does not necessar-ily imply a large amount of coseismicwork. Heterogeneities in density of the continental basement can therefore be related to complexities in the pattern of coseismic slip and in the aftershock distribution. Locally, a subducted seamount or seaward spur of high-density continental crust may be present near the high slip patch.