From the Atlas to the Variscan Core of Iberia: Progress on the Knowledge of Mantle Anisotropy from SKS Splitting

The data provided by the dense Iberarray broad-band seismic network deployed in the framework of the large-scale TopoIberia project, as well as from permanent broad-band stations operating in Morocco, Portugal and Spain has allowed to get a large scale view of the anisotropic properties of the mantle beneath the western termination of the Mediterranean region and its transition to the Atlantic ocean. In this contribution we will gather the previously presented results with the analysis of the data provided by IberArray stations in the central part of Iberia, broad-band OBSs deployments in the Alboran Sea and the Gulf of Cadiz and new seismic networks deployed in the High Atlas and the Moroccan Meseta. The High Atlas has been investigated using data from a broad-band network installed by the Univ. of Munster with a primary focus on the study of the properties of the deep mantle. Additionally, up to 10 Iberarray stations have been shifted southward to complete the survey along the Atlas and to investigate the Moroccan Meseta. In agreement with the results presented by the Picasso team along a profile crossing the Atlas northward, the anisotropy observed in this area is small (0.6 - 0.9 s) with a fast polarization direction (FPD) oriented roughly E-W. It is important to note that there is a very significant number of high quality events without evidence for anisotropy. This may be the result of the combined effect of two or more anisotropic layers or of the presence of a large vertical component of flow in the upper mantle. Moving northwards, the first TopoIberia-Iberarray deployment in the Betics-Alboran zone has evidenced a spectacular rotation of the FPD along the Gibraltar arc following the curvature of the Rif-Betic chain, from roughly N65E beneath the Betics to close to N65W beneath the Rif chain. To complete this image, we have now processed data from two OBS deployments in the Alboran Sea and Gulf of Cadiz installed by Geomar as part of the TopoMed project. The short period of registration and the intrinsic problems related to noise and instrument stability in the seafloor has not allowed getting a large database of anisotropic measurements. However, the few events providing good quality SKS measurements show interesting results which may provide significant clues to the knowledge of the geodynamic evolution of this area. Beneath Iberia, the second Iberarray deployment encompasses mainly the Variscan units of the Central Iberian Massif. The results show a small amount of anisotropy and suggest complex anisotropy features, confirming what has been observed in the first deployment. A significant change in both FPD and delay times across the two main units of the Variscan domain, the Ossa-Morena and the Central Iberian zones seem to exist. Permanent stations in southern Portugal show a significant number of null measurements, similar to what has previously discussed for the High Atlas stations. Beneath Eastern Iberia, the FPD have a roughly E-W orientation. No significant changes are observed between the anisotropic parameters beneath the Balearic Islands and those in the Eastern Betics.