Structure and evolution of the Gibraltar Arc (western Mediterranean) from seismic tomography

Abstract

We present new tomographic images of the Iberian Peninsula and northern Morocco based on broadband seismic data from the IberArray experiment, complemented with other permanent stations from local and regional networks. The quality of this combined dataset allows to apply a number of imaging techniques, including local and teleseismic travel- time tomography, surface-wave tomography from regional and distant earthquakes, and surface-wave tomography from correlations of seismic ambient noise. Each of these methods has advantages and disadvantages, and the combination of all allows to obtain a detailed and consistent picture of the crustal and mantle structure beneath the Iberian Peninsula and Morocco. Using local earthquake and seismic ambient noise tomography we are able to image the shallow crustal structure, also in regions with low seismicity. In particular we have obtained constraints on the lateral and vertical extent of the major sedimentary basins (Gulf of Cadis, west Alboran basin, Valencia trough, and Ebro basin) and the areas of greater than average crustal thickness beneath the mountain ranges of the Rif, Betics, Iberian chain and Pyrenees. Teleseismic travel-time tomography is best suited to investigate the structure of the upper mantle. Using very precise travel-time measurements determined using waveform similarity we have obtained a well resolved image of a high velocity anomaly beneath the Betics and Alboran Sea that extends down to the mantle transition zone and probably corresponds to a subducted slab.