Howard A. Zebker

Fault Slip Distribution of the 1999 Mw 7.1 Hector Mine, California, Earthquake, Estimated from Satellite Radar and GPS Measurements

We use a combination of satellite radar and GPS data to estimate the slip distribution of the 1999 M w 7.1 Hector Mine Earthquake, a right-lateral strikeslip earthquake that occurred on a northwest–southeast striking fault in the southern California Mojave Desert. The data include synthetic aperture radar interferograms (InSAR) from both ascending and descending orbits, radar amplitude image offset fields (SARIO) for both ascending and descending azimuth directions, and campaign GPS observations from 55 stations provided by Agnew et al. (2002). We model the fault with nine segments derived from the field-mapped fault rupture, the SARIO data, and aftershock locations. We first estimate the dip of each fault segment, as well as a single constant strike-slip component across each segment, resulting in an average dip of 83° to the northeast and slip of up to 5.6 m. Then, we fix the optimal fault segment dip, discretize the fault segments into 1.5 km × 1.5 km patches, and solve for the variable slip distribution using a nonnegative least-squares method that includes an appropriate degree of smoothing. Our preferred solution has both right-lateral strike-slip and reverse faulting. The estimated geodetic moment is 5.93 × 10 19 N m ( M w 7.1), similar to seismological estimates, indicating that there are insignificant interseismic and postseismic deformation signals in the data. We find strike-slip displacements of up to 6.0 m and reverse faulting of up to 1.6 m, with the maximum slip located just northwest of the epicenter. Most of the slip is concentrated northwest and south of the epicenter; little slip is found on the northeastern branch of the fault. The SARIO data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field.