Mantle Flow Beneath a Continental Strike-Slip Fault: Postseismic Deformation After the 1999 Hector Mine Earthquake

Abstract

Two recent large earthquakes in the Mojave Desert, California—the magnitude 7.3 1992 Landers and magnitude 7.1 1999 Hector Mine earthquakes—have each been followed by elevated crustal strain rates over periods of months and years. Geodetic data collected after the Hector Mine earthquake exhibit a temporally decaying horizontal velocity field and a quadrant uplift pattern opposite to that expected for localized shear beneath the earthquake rupture. We interpret the origin of this accelerated crustal deformation to be vigorous flow in the upper mantle in response to the stress changes generated by the earthquake. Our results suggest that transient flow in the upper mantle is a fundamental component of the earthquake cycle and that the lower crust is a coherent stress guide coupling the upper crust with the upper mantle.