Influence of lithospheric and mantle stratification on co- and post-seismic deformation due to finite faults

Coseismic and post-seismic deformation in the fully relaxed state following large earthquakes is modelled for finite faults by means of multilayered, viscoelastic, self-gravitating, hydrostatically pre-stressed, spherical ear th models based on the preliminary reference earth model (PREM) with a Maxw ell rheology. For both finite dip-slip and strike-slip sources we find that the elastic layering of the lithosphere has a major impact on the modellin g of co- and post-seismic deformation. For large and deep earthquakes embed ded at the base of the lithosphere in the proximity of the lithosphere-uppe r mantle interface in order to study the effects of mantle relaxation, cose ismic and postseismic deformation can result in several tens of centimetres of displacement, with a deformation pattern strongly dependent on the dist ance from the source and the azimuth from the strike of the fault. Strike-s lip faulting is found to be more sensitive to mantle rheology than dip-slip faulting. Deviations between earth models with a homogeneous crust and lit hosphere and those based on PREM are of the same order as the coseismic and post-seismic signals, ranging from a few centimetres to several tens of ce ntimetres for large earthquakes with seismic moments of 10(22) N m and epic entral depths of 75-100 km at the base of the lithosphere. This finding len ds further support to the conclusion of a preliminary study based on dip-sl ip point sources that observations based on VLBI, GPS and SAR techniques, w hich can easily resolve crustal deformation of the order of the deviations among the various lithospheric models, can be badly misinterpreted if the r esults of surveying in seismogenic regions are compared with earth models t hat have a limited number of layers in general and a homogeneous crust in p articular.