Abstract
Abstract. Recently acquired swath-bathymetry data and high-resolution seismic reflection profiles offshore Adra (Almería, Spain) reveal the surficial expression of a NW–SE trending 20 km-long fault, which we termed the Adra Fault. Seismic imaging across the structure depicts a sub-vertical fault reaching the seafloor surface and slightly dipping to the NE showing an along-axis structural variability. Our new data suggest normal displacement of the uppermost units with probably a lateral component. Radiocarbon dating of a gravity core located in the area indicates that seafloor sediments are of Holocene age, suggesting present-day tectonic activity. The NE Alboran Sea area is characterized by significant low-magnitude earthquakes and by historical records of moderate magnitude, such as the Mw = 6.1 1910 Adra Earthquake. The location, dimension and kinematics of the Adra Fault agree with the fault solution and magnitude of the 1910 Adra Earthquake, whose moment tensor analysis indicates normal-dextral motion. The fault seismic parameters indicate that the Adra Fault is a potential source of large magnitude (Mw ≤ 6.5) earthquakes, which represents an unreported seismic hazard for the neighbouring coastal areas.
Highlights
Seismogenic faults may be silent in the instrumental and historical periods and, their seismic potential may remain inadvertently hidden
We focus on the area located to the west of the Carboneras Fault, in the Adra–Almerıa margin in
The new data shows that the Adra Fault is active given that it affects all the sedimentary sequences, cutting the uppermost units, which based on dates from sediment core CIM-4 are of late Holocene age (Fig. 5)
Summary
Seismogenic faults may be silent in the instrumental and historical periods and, their seismic potential may remain inadvertently hidden. A continuous effort has been made to adapt the paleoseismological approach to the slow active faults of the southeastern Iberian margin that accommodate the convergence between the Iberian and African plates (e.g. Martınez-Diaz et al, 2001; Martınez-Dıaz and Hernandez-Enrile, 2004; Masana et al, 2004, 2005; Gracia et al, 2006, 2010; Moreno et al, 2008) This approach, which considers the offshore faults, is crucial for estimating realistic values of the seismic hazard in this area largely based on the relatively short period of instrumental (< 100 yr) and historical (< 2000 yr) earthquake catalogues for the Iberian Peninsula (e.g. Pelaez and Lopez Casado, 2002)
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