AF: Inst. Andaluz de Ciencias de la Tierra (CSIC-Granada Univ.), Campus Fuentenueva s/n, Granada, 18002 Spain
AB: The Alboran Sea (Westernmost Mediterranean) is located in the inner part of an arcuate Alpine orogenic belt comprised by the Betic and Rif, connected through the Gibraltar Arc. The boundary between the African and Eurasian plates in the Betic-Rif-Alboran region is a large zone of diffuse deformation and strain partitioning with simultaneous extension and lithospheric attenuation. In fact, the distribution of local seismicity is quite variable, with scattered seismic swarms which spread out over a broad area of plate convergence deformation. Focal depth distribution of earthquakes shows that most of seismicity is located in the crust (86%), and preferentially in the upper, brittle crust (90% of the crustal seismicity at $<$15 km). A three dimensional rheological model has been developed in the region to characterize the brittle-ductile transition (BDT); calculating a multiple set of regularly-spaced strength profiles based on a synthetic 3D lithospheric structure that gathers most of the available geological and geophysical data. Additionally, data from geodetic measurements of crustal deformations and earthquakes focal mechanisms have been used to validate the boundary conditions that govern the rheological model. Predicted rheological domains in the crust, either brittle or ductile, agree with focal depth distribution of crustal earthquakes in the westernmost Mediterranean; moreover, the scarce micro-seismicity located in the lithosphere mantle ($<$14%) is also in agreement with these results. Most of the seismicity tends to nucleate in the brittle domains, up to the BDT, resulting in a gap between uppermost crustal and lithosphere mantle intermediate seismicity. In spite of seismic swarms that seem to depict active faults, it is needed to apply relative location methods to constrain the prolongation in depth of active faults. This sort of comparison between the rheological modelling results and the distribution of seismicity in the Westernmost Mediterranean provides important clues for any attempt to constrain the strain velocity field related to the Africa and Eurasia plate convergence. This type of study in the Betic-Rif-Alboran crustal domain deserves to integrate the geometry and timing of active faults, to unravel the link between these structures and active mountain uplift (and coeval subsidence) processes.
DE: 7230 Seismicity and seismotectonics
DE: 8107 Continental neotectonics
DE: 8159 Rheology--crust and lithosphere
DE: 8164 Stresses--crust and lithosphere
DE: 7205 Continental crust (1242)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting