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Active Faulting on the Coral Patch Ridge Area (SW Iberian Margin) Based on High-resolution PSDM Seismic Profiles: Significance for Earthquake and Tsunami Hazard

Sara Martínez-Loriente, Eulàlia Gràcia, Rafael Bartolome, Christopher Connors, Valenti Sallares, Hector Perea Manera, Claudio Lo Iacono, Dirk Klaeschen, Juanjo Dañobeitia, and Nevio Zitellini

The external part of the Gulf of Cadiz is an area of great interest where have been nucleated large historical and instrumental earthquakes, such as the 1755 Lisbon Earthquake (Mw 8.5) and the 1969 Horseshoe Earthquake (Mw 8.0). The NW-SE convergence of the African and Eurasian Plates controls the seismic activity of moderate magnitude that characterizes the region. Multi-scale acoustic and seismic reflection profiles acquired on the external part of the Gulf of Cadiz during the SWIM-2006 survey reveal active faulting and folding affecting the preexisting structures formed during the Jurassic and Cretaceous rifting. The present study focuses on the characterization of the tectonic pattern and timing of deformation associated to the active structures located south from 36.553251 N (deg). This region embraces a prominent NE-SW trending structure, the Coral Patch Ridge (CPR), which is bounded by the Horseshoe and Seine abyssal plains (HAP, SAP). E-W trending dextral strike-slip faults showing surface deformation and flower structure geometry predominates across the HAP, whereas NE-SW-trending thrust faults characterize the structures of the CPR and SAP. A pre-stack Kirchhoff depth-migration (PSDM) was performed to selected SWIM-2006 profiles to obtain the correct and real geometry of these structures which allowed us to build a regional cross-section and restore it to the non-deformed stage. Then, we calculate the shortening of the lithosphere in this region due to the compressive regime occurring since the Oligocene. Furthermore we have evaluated the seismic potential of these active faults based on the calculation of their seismic parameters (geometry, kinematics, slip-rate, maximum magnitude). The results show that although the CPR, HAP and SAP areas are characterized by a subdued seismic activity, the active structures located there are able to generate large magnitude earthquakes (Mw > 7.0), thus implying a significant earthquake and tsunami hazard previously unaccounted.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013