Submarine Active Faults and Morpho-Tectonics Around the Iberian Margins: Seismic and Tsunamis Hazards

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.

Networks of geometrically coherent faults accommodate Alpine tectonic inversion offshore SW Iberia

“…Generalised uplift of West Iberia's coastline is also recognised in the Pliocene-Quaternary and, locally, during major seismo-tectonic events such as the 1755 Lisbon Earthquake, which uplifted the Atlantic coast of Iberia in several locations (Silva et al, 2023). Neotectonic activity is also clear near reactivated structures such as the Pereira de Sousa Fault, the São Vicente Fault and multiple areas offshore Algarve (Terrinha et al, 2009;Somoza et al, 2021).…”

Neogene and Pleistocene geodynamics: the paleoseismic evolution of Armorica (Western France)

“…Because the Tortono-Messinian interval represents six eustatic cycles (Hardenbol et al, 1998), these are probably represented by the Cockburn Fm (Upper Miocene) and possibly the Pliocene Little Sole Fm (Zanclean to Gelasian) under a thin cover of middle to recent Quaternary (Le Roy et al, 2011). In the Western Approaches (Le Roy et al, 2011), the Garlizenn−1 core clearly reveals this succession, based on micropaleontological data (geological map Ouessant sheet 1/250,000), such as the well-dated record from offshore of Iberia (Somoza et al, 2021). This seems also valid for the Cenozoic early history of the Hurd Deep issued from seismic profiles (Bourillet et al, 2003).…”

Cinemática de fallas normales menores tardi- post-variscas en la sección costera de la ría del Eo (N de España)

“…En el sector atlántico, se caracteriza por una extensión continental aproximada O-E que culmina con la formación de varios miles de kilómetros de corteza oceánica y un adelgazamiento de la corteza continental (p. ej., Vázquez et al, 2008;Nirrengarten et al, 2018;Somoza et al, 2021). En el margen continental cantábrico se han descrito numerosas estructuras extensionales sumergidas que muestran una geometría coherente con la extensión N-S (Cadenas y Fernández-Viejo, 2017), pero en el continente, estas estructuras son menos reconocibles al haber sido afectadas por la deformación compresiva posterior durante el ciclo alpino (p.…”