Recent and present-day stresses in the Granada Basin (Betic Cordilleras): Example of a late Miocene-present-day extensional basin in a convergent plate boundary

The diffuse convergent boundary between the Eurasian and African plates in the western Mediterranean is associated with a seismicity zone more than 30 0 km wide. Although the two plates are converging NW-SE, the Betic and Rif Cordilleras contain extensional structures that have been active since the Miocene. The extensional tectonics in the region, which occurred simultaneo usly with the uplift of the cordillera, have been analyzed in the southeast ern sector of the late Miocene to recent Granada Basin, using earthquake fo cal mechanisms, the determination of paleostresses from the study of the or ientation and kinematics of microfaults, and the study of the major structu res. Both the geological surface data and the focal mechanisms indicate pre sent-day regional conditions of NE-SW extension, with triaxial to prolate s tress ellipsoids. However, the stress field is heterogeneous, with local va riations in stress over time, with different stresses sometimes even acting simultaneously in adjacent areas. The most frequent changes consist of plu ridirectional or NE-SW extension, favored by the prolate character of the s tress ellipsoids, and NW-SE subhorizontal compression, favored by the regio nal tectonic setting. Strike-slip faults are scarce even though they are th e most likely structure to be expected in a region with SW-NE extension and NW-SE compression. Seismicity is concentrated in the upper crust and may c orrespond to the activity of low- to high-angle normal faults similar to th e surface faults, although they can not be correlated with them. The lower cutoff of this seismicity probably coincides with the 300 degrees C isother m and suggests a low thermal gradient for the region. Present-day regional stresses have sigma(1) vertical at the surface but in depth plunge toward t he SW.