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Resumen:
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We have applied the analytic model of general triclinic transpression with oblique extrusion to an active shear zone in southeastern Spain. This study opens a new methodological approach in the study of active fault zones. We are able to constrain the triclinic transpression model with absolute measures of active deformation, such as GPS velocity gradients, and have exhaustively explored the predictions of the model and compared them to the orientation data of field kinematic markers (fault-slip data and reorientation of fold hinges during progressive deformation), GPS data and the kinematic study of the fault gouge that is developed at the Alhama de Murcia Fault. The combined analysis allows the values of the kinematic vorticity number, the orientation of the vorticity vector, the orientation of the local and regional convergence vectors, the angle of extrusion in the shear zone and the amount of extrusion to be constrained. The results point to a highly partitioned heterogeneous shear zone with domains deforming in response to the same boundary conditions but are displaying different kinematic responses that reflect both their intrinsic properties and geometric effects related to competency contrasts. We propose that the Alhama de Murcia Fault is an incompletely coupled fault zone with two different domains: a low competency domain comprising the fault gouge, ductilely deformed, with low vorticity values, which probably experienced a steady-state, aseismic slip that reflects regional convergence vectors (convergence Eurasia–Nubia); and a domain outside of the fault gouge with episodic brittle failure, with higher vorticity values and showing convergence vectors which are parallel to the local convergence vectors calculated from the GPS velocity field.
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