Investigating the 1996 Pyrenean Earthquake (France) with SAR interferograms heavily distorted by atmosphere

Abstract

We form interferograms by pairwise combination of four synthetic aperture radar (SAR) images acquired by the ERS‐1/2 satellites before and after the ML 5.2, earthquake of February 18, 1996 near Saint‐Paul de Fenouillet in the eastern Pyrenees, France. Of the four interferograms we interpret, two span the seismic event. The interferometric fringes, which correspond to contours of equal satellite‐to‐ground line length change (28.4 mm), are distorted by atmosphere in such a way that the amplitude of the coseismic signature is much smaller than that of the atmospheric disturbances. These noisy conditions contrast with previous earthquake studies with radar interferometry. Nevertheless, we are able to obtain a realistic elastic dislocation model fitting the observations. By comparisons with forward modeling, our results can discriminate between competing models that are not resolved by previous seismological studies. The data derived from radar are especially useful for a more accurate characterization of the vertical motion.