Sismicidad, sismotectónica y evolución geodinámica de la Península Ibérica

Abstract

Several studies during last years had been performed to understand the plate contact between Eurasia and Africa. Main reasons are the importance of this first order contact between plates which in its cen- tral part corresponding to the Alboran Sea is of great geodynamic interest and also because the important events related such as the Lisbon Earthquake of 1755. The three parts in which can be divided this part are the Gorringe Bank-Gulf of Cadiz, the Alboran Sea and the northern coast of Africa throughout Algeria. The seismicity for the area is presented for three different depth ranges: shallow (less than 35 km), intermediate (above 60 km) and deep ones with a moment magnitude assignment to each event. Besides that, the state of stress is analyzed considering the focal mechanism solutions of events grater than M=5 which may be related to the regional stress field acting in the zone ignoring the local state of stress obtained though the study of lower magnitude events. However, for the central part of the contact coincident with the Alboran Sea, as the intermediate seismic activity recorded is of lower magnitude we considered the focal mechanism solutions given for lower magnitude events. The first conclusion we have obtained is that for the Gorringe Bank-Gulf of Cadiz leg and the Algeria system of faults there is almost horizontal compression acting in the NNW-SSE direction along a thrust fault system. In relation to the shallow Alboran Sea seismicity a horizontal compression is acting in a variable NW-SE to N-S directions. Nevertheless, if we study intermediate events the acting horizontal pressure axes are in NE-SW direction which change to NW-SE as far as we reach deeper events. Finally we analyze the geodynamic models proposed for the Alboran Basin trying to reconcile the existence of a extensional basin in a compressive regime. From all proposed models the one based on a delamination process is the one which explain not only the seismicity and focal mechanism data but also the seismic tomography, gravity and attenuation of shear waves data.