Crustal structure beneath Spain from deep seismic sounding experiments

Abstract

Major tectonic units of Spain have been investigated by deep seismic sounding experiments since 1974 to determine crustal structures and to delineate their differences. These areas are the central part of the Hercynian Meseta, and the Alpine chains: the Betic Cordillera in the south, including the Balearic promontory and the Alboran Sea, and the Pyrenees in the north. The main features of the crust and the upper mantle along a NNE-SSW cross-section from the Pyrenees to the Alboran Sea are described. The crust under the Meseta is typical of Hercynian areas found elsewhere in Europe, with an average thickness of 31 km, whereas the two Alpine regions are characterized by very large lateral inhomogeneities, such as rapid thickening of the crust to 50 and 40 km under the Pyrenees and the Betics, respectively. The deep-reaching E-W-trending North Pyrenean fault has a throw of 10-15 km at the base of the crust. A Pn velocity of 8.1 km s-1 is found under the entire Iberian Peninsula. In the Alboran Sea, strongly varying thicknesses of sediments, shallow variable depths to the Moho (∼ 13 km under the Alboran ridge), and strong variations of Pn velocity between 7.5 and 8.2 km s-1 have been found. © 1983.