Crustal rheology and seismicity in the Gibraltar Arc (western Mediterranean)

Abstract

On the basis of the lithospheric structure of the Gibraltar Arc (western Mediterranean), we constrain depth distribution of crustal seismicity and active tectonics by means of rheological modeling. Crustal yield strength and depth of the brittle-ductile transition zone (BDT) mimic the curvature of the arc with maximum depths of 12-9 km whereas in the Betics and Rif, BDT shallows eastward (to 6-5 kin depth), oblique to crustal thickening. Most of the crustal seismicity (>60%) is placed within the brittle crust, decaying exponentially in the ductile crust. Active faults observed in surface geology, control the present topography of the Betics, connect in depth with scattered seismic swarms, and merge into the BDT. This horizon is interpreted as a decoupling horizon that conditions the mode of present-day deformation partitioning. Below the BDT, low-strength domains enable crustal flow under central Betics promoting stress rotation and topographic uplift. Copyright 2008 by the American Geophysical Union.