The lithosphere of Iberia has been formed through a number of processes of continental collision and extension. In Lower Paleozoic, the collision of three tectonics blocks produced the Variscan Orogeny, the main event of formation of the Iberian lithosphere. The subsequent Mesozoic rifting and breakup of the Pangea had a profound effect on the continental crust of the western border of Iberia. Since the Miocene, the southern interaction between Africa and Iberia is characterized by a diffuse convergent margin that originates a vast area of deformation. The impact of this complex tectonic in the structure of the Iberian Lithosphere remains an incognito, especially in its western part beneath Portugal. While the surface geology is considerably studied and documented, the crustal and lithospheric structures are not well constrained. The existing knowledge relating the observed surface geology and Lithospheric deep structures is sparse and sometimes incoherent. The seismic activity observed along West Iberia is intensely clustered on few areas, namely on north Alentejo, Estremadura and Regua-Verin fault systems.
Some of the problems to address are: What is the relation between surface topography and the deep crustal/lithospheric structure? How was it influenced by the past tectonic events?
Which was the deep driving factor behind the tectonic units observed at surface: Lithosphere-Astenosphere boundary structure or deeper mantle structure? How the upper mantle and the Lithosphere-Astenosphere transition zone accommodated the past subduction? Which is its role and influence of the several tectonic units, and their contacts, in the present tectonic regime and in the stress field observed today? Is the anomalous seismicity and associated crustal deformation rates, due to an inherited structure from past orogenies?
The main goal of this work is a 3D detailed image of the “slice” of the Earth beneath Western Iberia, by complementing the permanent seismic networks operating in Portugal and Spain. The different scales involved require the usage of several passive seismological methods: Local-Earthquake Tomography for fine structure of seismogenic areas, ambient noise tomography for regional crustal structure, Receiver Functions for Lithospheric structure and Surface-wave tomography for large scale Listosphere-Astenosphere structure. Crustal and Mantle seismic anisotropy analysis, coupled with source analysis and correlation with current geodetic measurements will allow establishing a reference 3D anisotropy model of present and past processes.
