Comparison of Four Moderate-Size Earthquakes in Southern California Using Seismology and InSAR

Source parameters determined from interferometric synthetic aperture radar (InSAR) measurements and from seismic data are compared from four moderate size (less than M 6) earthquakes in southern California. The purpose is to verify approximate detection capabilities of InSAR, assess differences in the results, and to test how the two results can be reconciled. First, we calculate the expected surface deformation from all earthquakes greater than magnitude 4 in areas with available InSAR data. A search for deformation from the events in the interferograms yielded 4 possible events with magnitudes less than 6. The search for deformation was based on a visual inspection as well as cross-correlation in 2-D between the measured signal and the expected signal. A grid-search algorithm was then used to estimate focal mechanism and depth from the InSAR data. The results were compared with locations and focal mechanisms from published catalogs. An independent relocation using seismic data was also performed. For the three events that show clear surface deformation, the radar data was unable to improve the epicentral (latitude and longitude) location as the seismic locations fell within the expected rupture zone. However, the InSAR data provides tighter control on