A tomographic study of the lithosphere beneath the Pyrenees from local and teleseismic data

Abstract

The upper crust appears very heterogeneous and exhibits sharp velocity contrasts. In the uppermost 7 km, an east-west trending zone with velocities up to 6% higher than the surrounding material is observed all along the Pyrenees. In the central and eastern Pyrenees, two large, high-velocity bodies stand out in the North Pyrenean Zone and extend down to the base of the upper crust. They coincide with large positive gravity anomalies and are interpreted as lower crust or upper mantle blocks uplifted into the upper crust. The lower crust is poorly resolved but appears to be less heterogeneous than the upper crust. Moreover, the lower crustal structure is almost uncorrelated with the upper crustal structure. In the upper mantle, P models are derived from the travel times of the remote events recorded at the Pyrenean stations. The most important feature is the presence, in the eastern and central Pyrenees, of a vertical, low-velocity heterogeneity south of the North Pyrenean Fault down to 80-100 km. -from Authors