ESTIMATION OF AN EARTHQUAKE FOCAL MECHANISM FROM A SATELLITE RADAR INTERFEROGRAM - APPLICATION TO THE DECEMBER 4, 1992 LANDERS AFTERSHOCK

Using the interferometric fringes generated by the phase difference between a pair of synthetic-aperture radar (SAR) images acquired by the ERS-1 satellite, we estimate the focal mechanism of a small, shallow thrust earthquake. The inversion procedure is an iterative, linearized least-squares algorithm based on a standard elastic dislocation formulation for coseismic displacements. Our preferred estimate is a thrust focal mechanism with its hypocenter at (N34.35 degrees +/- 0.4 km, W116.91 degrees +/- 0.2 km, 2.6 +/- 0.3 km depth) on a plane dipping southward beneath the San Bernardino Mountains, with a moment magnitude (Mw) of 5.4. The strike, dip, and rake are N106 degrees E +/- 7 degrees, 28 degrees +/- 4 degrees, and 93 degrees +/- 4 degrees, respectively on a fault 3.1 +/- 0.5 km wide and 2.9 +/- 0.4 km long. The precision of these estimates is competitive with seismological determinations.