Postseismic fluid flow after the large subduction earthquake of Antofagasta, Chile

We interpret the time evolution of high P-wave to S-wave velocity (Vp/Vs) r atios after the large Antofagasta subduction earthquake (M-W = 8.0) as due to postseismic. fluid flow into the overriding plate. We suggest that accum ulation of high stress forms a permeability barrier along the plate interfa ce, capturing the fluids in the subducting plate. This seal is broken only by large subduction earthquakes that allow the fluids to rapidly migrate in to the overlying plate. Postseismic fluid flow implies a relatively high pe rmeability of the overlying lower continental crust, which we estimate to b e 10(-16) to 10(-17) m(2).