P Wave Tomography of the Western Mediterranean Region and the Gulf of Cadiz. Constraints on Regional Geodynamic Models

Abstract

e, to map with an improved resolution, the lateral velocity variations of the mantle lid in the Western Mediterranean region and the Gulf of Cadiz. This tomography reveals that all the recent shallow large instrumental earthquakes (Mag ≥ 6.5) in the Maghreb region and in the Gulf of Cadiz, have all occurred in areas where (a) the mantle lid is cold with velocities larger than 7.95 km/sec, (b) significant lateral mantle lid velocity variations occur around these areas, in particular in the region where has occurred the 1755 Lisbon earthquake (Mag = 8.5-9.0). A vey hot mantle lid is observed in the Alboran Sea; consistent with a delamination of the westward underthrusted oceanic plate in the Gulf of Cadiz; whose cold shadow edge, is well outlined by the tomography. The thermal effect associated to the Calabrian Arc wedge, extends westward in the Mediterranean sea, on wavelength of at least 700 km. It contributes to warm the continental lithosphere of the northern edge of the eastern part of the Tellian Atlas, preventing it to nucleate large earthquakes.