Abstract

We interpret the time evolution of high P-wave to S-wave velocity (Vp/Vs) ratios after the large Antofagasta subduction earthquake (Mw = 8.0) as due to postseismic fluid flow into the overriding plate. We suggest that accumulation of high stress forms a permeability barrier along the plate interface, capturing the fluids in the subducting plate. This seal is broken only by large subduction earthquakes that allow the fluids to rapidly migrate into the overlying plate. Postseismic fluid flow implies a relatively high permeability of the overlying lower continental crust, which we estimate to be 10−16 to 10−17 m2.

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