Measuring near field coseismic displacements from SAR images: application to the Landers earthquake

We describe a procedure to compute SAR interferograms based on the compensation of the images' misregistrations due to the ground deformation and on a specific adaptive filtering to improve the SNR in the measurement where displacement gradients are large. Applied to the Landers earthquake case, the registration reduces the phase noise by 20 degrees (rms) near the fault and the interferogram reveals fringes that would not show out otherwise. The interferogram is validated by comparison, in the far field, with a GPS/EDM-based model. The inferred displacement field shows discontinuities that follow the fault within few hundred meters. Close to the fault the measured displacements differ significantly from that predicted by elastic modeling of the farfield data. Interferometry and measurements derived from the images' amplitude (offsets) appear to be complementary techniques providing original measurements that may help to reconcile seismological and geodetic models of coseismic deformation with measurements of fault-slip at the surface.