A comparison between short term (coseismic) and long term (one year) slip for Landers eathquake: Measurements from strong motion and SAR interferometry

Bruno Hernandez, Fabrice Cotton, Michel Campillo
Laboratoire de Géophysique Interne et Tectonophysique, Université Joseph Fourier, Grenoble, France

Didier Massonnet
Centre National d'Etudes Spatiales, Toulouse, France

Abstract. The relative surface displacement in the region of the Landers earthquake were measured for a time interval of about 1 year using SAR interferometry (Massonnet et al., 1993). On the other hand, we evaluate the coseismic slip distribution on the fault through strong motion inversion (Cotton and Campillo, 1996). We use these results to compute the static displacement field associated with the coseismic slip. The synthetic statics and the interferometry and GPS measurements are in a very good agreement. We present an attempt to invert the geodetic data to retrieve the associated slip distribution on the fault. The analysis of the final population in a genetic inversion shows that this type of data does not allow to resolve the slip distribution at depth. As a consequence we cannot compare directly the inversion results for the slip distribution on a 1 year period and the coseismic slip. In order to evaluate the magnitude of the pre- and post-seimic slip, we computed a residual interferogram between SAR data and synthetic coseismic displacement. A simple analysis of the residuals gives limiting values of the amplitude of pre- and post-seismic slip which are at least one order of magnitude smaller than the coseismic slip.