Lateral variations in the deep crustal structure at the Iberian margin of the Valencia trough imaged from seismic reflection methods

Abstract

New seismic images of crustal structure have been obtained in an area of western Europe where attenuation of the continental crust by a factor of two has been reported previously. The deep lateral variations in velocity and reflectivity at the transition between the northeastern Iberian Peninsula and the Valencia trough are investigated with three seismic reflection data sets. First results of the Spanish deep vertical reflection ESCI-profile on the Iberian mainland extend the crustal image of the Ecors-Pyrenees profile to the Mediterranean coast. A highly-reflective zone about 15 km thick is imaged in the lower crust beneath the Ebro basin and the Catalan coastal ranges, where the Moho is located at 29 km depth. This deep reflective pattern appears to be disrupted by the effects of low-velocity sediments in the Neogene Reus basin, but continuity of the principal horizons is inferred from illuminations of the area using sources and receivers at wide-angle offsets. High-quality recordings up to 50 km inland of air-gun shots from the marine ESCI-profile provide a complementary image of the structure on land and show that the major crustal thinning toward the Valencia trough starts near the shoreline. The lateral variability of the crust is investigated using a second profile displaced 30 km to the northeast. Independent refraction and reflection interpretation techniques applied to this profile, which consisted of densely-spaced shots, resulted in consistent depth sections with crustal thinning beginning further inland. Thinning of 10 km takes place within 60 km at the Catalan margin. Moho-reflected waves (PMP) have been processed as far traces of a deep reflection profile. The processing included common midpoint (cmp) sorting, stacking and migration. The inferred lateral variations in deep crustal structure near the Catalan coast are consistent with the Bouguer gravity field. They may be related to episodes of extensional block faulting that have affected the Catalan-Valencian domain since Paleogene times. © 1994.