No 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.

New measurements, statistical analyses, and models support the conjecture that a large earthquake can trigger subsequent volcanic eruptions over surprisingly long distance and time scales.

Abstract. Viscoelastic relaxation of a ductile asthenosphere underlying a purely elastic plate is a strong candidate process for explaining anomalous rates of crustal deformation observed following large earthquakes. The nongravitational treatment of Pollitz [1992], which is valid on a global scale and includes the effects of compressibility, is here extended to permit the calculation of gravitational viscoelastic relaxation for a specified spherically layered viscoelastic rheology following an earthquake in an elastic layer. The simple approximations we adopt make the resulting treatment particularly suitable for near-field calculations. For an asthenosphere with a Maxwell rheology, the effect of gravitational coupling is manifested only many relaxation times after the earthquake, as obtained by previous investigators. Its effect is generally to speed up the long-wavelength component of the relaxation process and attenuate the overall vertical displacement pattern. Several subtle features common to the relaxation behavior from several different fault types (thrust, rift, and strike-slip) are identified. The effect of gravitational coupling on horizontal displacements is consistent with flexure of the upper elastic plate driven by the corresponding effects on the vertical displacement. Stress diffusion away from the source region generally exhibits pulse-like behavior which is dispersive in both space and time. If the asthenosphere is confined to a relatively narrow channel, then the dispersion branches governing relaxation are radically altered, and stress diffusion effects far from the coseismic rupture zone exhibit a complicated time dependence reflecting the competing tendencies of toroidal and spheroidal mode relaxation.

Abstract. The crust around the rupture zone of the 1992 Landers earthquake has continued to deform in the years following the earthquake at rates -3 times greater than pre-earthquake rates. We use a combination of Global Positioning System (GPS) and synthetic aperture radar