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International audience; We present the results of dynamic modeling of the western Mediterranean that accounts for observed global positioning system (GPS) surface deformation of the Alboran Sea and surrounding Rif and Betic Mountains as the result of the combined effects of relative motion of the Eurasian and Nubian plates, low strength in the Alboran Sea region and sub-lithospheric processes occurring beneath the External Rif domain. Assuming that the lithosphere behaves elastically over the short time period of the GPS observations, an elastic plate model is considered in our study, including an area of weak lithosphere (factor of 10) centered on the Alboran Sea and in which lateral boundary conditions consist of the Nubia-Eurasia oblique convergence. Sub-crustal processes are modeled by application of a horizontal traction on a small area (patch) at the base of the elastic plate. Our modeling studies demonstrate the need for sub-crustal or sub-lithospheric, southwestward-directed forcing to account for observed southwestward motion of the Rif and Betic domains. Based on the location, orientation, and small area of the traction patch, we hypothesize that forcing is associated with delamination and rollback of the subducted African continental lithospheric mantle beneath the External Rif zone, due to the pull of the oceanic part of the Western Mediterranean slab, a dynamic process that may be similar to that where the over-riding plate is driven toward the subduction zone during slab rollback.

Topography associated with normal faulting in the Basin and Range (western United States) is usually modeled as a flexure of a broken elastic plate. However, modeled effective rigidities are usually 100 times lower than the rigidity deduced from upper-crustal thickness. This discrepancy may be related to a significant anelastic deformation, which we explore through numerical modeling. Because experimental rock rheology evidences a pressure-dependent yield stress beyond the elastic limit in crustal rocks, we made a finite element model that accounts for such a crustal rheology and also for the frictional behavior of an embedded high-angle fault. Resulting topography after extension is similar to that obtained from a thin elastic plate model; however, the corresponding strain pattern differs. First, the footwall rotates in a rigid fashion over a width of 15 km that matches the typical size of uplifted Basin and Range blocks. Second, hanging-wall subsidence results from a significant horizontal extension and rotation of the crust. We suggest that plastic deformation in the deep part of the footwall could trigger the development of a new high-angle fault with a fault spacing that matches Basin and Range structure.