Abstract
The aim of this work is to make a synthesis at regional scale focused on the geophysical characterization of submarine faults around the Iberian margin to identify active structures and analyze their development in the framework of the present plate organization. Most of these submarine faults show seabed morphological expressions mapped with high-resolution swath bathymetry data, high-resolution parametric sub-bottom profiles and multichannel seismic profiles. Present active tectonics, deformation, seismicity, and tsunami-affected coastal areas is mainly focused on south Iberia at the Eurasian and Nubia plate boundary. Submarine active faults in these areas are represented by long strike-slip fault systems and arcuate fold-thrust systems. Their development takes place in response to present NW-SE convergence between the Eurasian and Nubia plates. We propose a strain partitioning model of the plate boundary into simple and pure shear zones to explain the distribution and mechanisms of active submarine faults along the Gulf of Cádiz, Gibraltar Arc and Alborán Sea in response to the present-day shear stress orientation. Nevertheless, deformation is also focused in the NW Iberian margin. Thus, along the Galician and Portuguese margin, several submarine faults mapped as thrust fault systems with high-seismic activity along the Iberian ocean-continent transition reflect the re-activation of former structures. We suggest that submarine active faults in the NW and W Iberia are also the response to the eastwards transfer of short-offset transform faults of the Mid Atlantic Ridge into the oceanic Iberian along a weakness as the former plate boundary between the oceanic Iberia and Eurasia domains. The distribution and activity of submarine faults mapped in this work from geophysical and bathymetric data are in good agreement with geodetic data and focal mechanisms.
Highlights
The Iberian Peninsula is bounded by a Cenozoic convergent margin between the Eurasia and former Iberian plates along their northern edge (North and Northwest Iberian Margin), and by a complex transform boundary (Gulf of Cádiz and Alborán Sea) to the south, between the Eurasia and Nubia plates (Figure 1)
We review and map the main active submarine faults around the Iberian Margins, which are mainly concentrated along the southern Eurasia-African plate boundary (Figure 1B), along with re-activated tectonic structures related to the former Cenozoic subduction in the northern Iberian Margin
The Case of the SW Iberian Margin: Active Inversion of a Passive Margin The thrust system that affects the morphology of the SW Iberian margin locally controls the present-day bathymetry and the pathway of the Mediterranean Outflow Water as it flows along the Gulf of Cádiz middle continental slope from the Strait of Gibraltar (Figure 3)
Summary
The Iberian Peninsula is bounded by a Cenozoic convergent margin between the Eurasia and former Iberian plates along their northern edge (North and Northwest Iberian Margin), and by a complex transform boundary (Gulf of Cádiz and Alborán Sea) to the south, between the Eurasia and Nubia plates (Figure 1). Scaling the source characteristics of the February 12th, 2007, Mw 6.0 Horseshoe earthquake, it was suggested another fault with a length of 230–315 km as potential source (Stich et al, 2006) This led to relate the potential source of the 1755-Lisbon tsunami to largescale WNW-ESE dextral strike-slip faults affecting the sedimentary cover over the continental and the oceanic basements. These structures were identified on multichannel seismic profiles by Medialdea et al (2009b) and seabed mapping as SWIM (South West Iberian Margin) lineaments on the compilation of multibeam bathymetry made by Zitellini et al (2009) in the Gulf of Cádiz
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