The 1995 Kozani-Grevena (norther Greece) earthquake revisited : an improved faulting model from synthetic aperture radar interferometry

International audiencePreviously, geodetic data associated with earthquakes have been widely modelled using coplanar rectangular dislocations in an elastic half-space. However, such models appear inadequate when complex geometries such as variations in strike and dip or multiple fault segments are involved. Here we revisit the 1995 M s = 6.6 Kozani-Grevena earthquake, and use synthetic aperture radar (SAR) interferometric measurements, tectonic observations and seismological data to constrain a fault model with a realistic geometry. We undertake a critical analysis of all available SAR data, including characterization of atmospheric artefacts. These are partially removed and the possibility that such effects are misidentified as secondary faulting is examined. Three well-correlated interferograms provide an accurate and complete description of the ground deformation field associated with the event. To take into account the complexity of the fault system activated during the earthquake, we construct a 3-D fault model, composed of triangular elements, that is geometrically more consistent with surface ruptures than those of previous studies. Using first trial-and-error and then iterative inversion, we explore the ranges of geometric parameters that can explain the data. We obtain an average final model and its standard deviation, with small slip amplitude at the surface, consistent with the field observations, and with slip as large as 2.5 m at depth. This model is compared with those previously published. We conclude that an antithetic fault is not required to explain the SAR data