Present‐day stress field in the Gibraltar Arc (western Mediterranean)

Abstract

The Gibraltar Arc in the western Mediterranean consists of the Betic and Rif Alpine chains and the Alboran Sea Basin. Four types of stress indicators (wellbore breakouts, earthquake focal plane mechanisms, young geologic fault slip data, and hydraulic fracture orientations) indicate a regional NW–SE compressive stress field resulting from Africa‐Eurasia plate convergence. In some particular regions, deviations of SHmax are observed with respect to the regional stress field. They are gentle‐to‐moderate (22°–36°) anticlockwise rotations located along the North Alboran margin and moderate‐to‐significant (36°–78°) clockwise rotations around the Trans‐Alboran Shear Zone (TASZ). This is a broad fault zone composed of different left‐lateral strike‐slip fault segments running from the eastern Betics to the Alhoceima region in the Rif and resulting in a major bathymetric high in the Alboran Sea (the Alboran Ridge fault zone). Some of these stress rotations appear to be controlled by steep gradients of crustal thickness variation across the North Alboran margin and/or differential loading imposed by thick sedimentary accumulations in basin depocenters parallel to the shoreline. Other stress perturbations may be related to active left‐lateral, strike‐slip deformation within the TASZ that crosscuts the entire orogenic arc on a NE–SW trend and represents a key element to understand present‐day deformation partitioning in the western Mediterranean.

Recent and active faults and folds in the central-eastern Internal Zones of the Betic Cordillera

“…This continent collision is still active at a rate of 4-5 mm/yr (Argus et al, 1989;DeMets et al, 1990DeMets et al, , 1994 and continues driving the development of active folds and faults (e.g., Sanz de Galdeano et al, 1995;Galindo-Zaldívar et al, 2003). Therefore, current displacement of the Earth's surface reveals the oblique convergence between the Iberian and African plates, showing a movement of the Eurasian plate and the Betic Cordillera toward the SSW/SW with respect to the African plate (Stich et al, 2006;Fadil et al, 2006;Tahayt et al, 2008;Vernant et al, 2010), which is roughly in accordance with the present-day stress setting (e.g., Fernández-Ibáñez et al, 2007;Pedrera et al, 2011).…”

Testing the sensitivity of geomorphic indices in areas of low-rate active folding (eastern Betic Cordillera, Spain)

“…Seismological data reveal a low to moderate seismicity with diffuse distribution (e.g., IGN, 2008). Earthquake focal solutions obtained in the Eastern Betics also support the NW-SE compression (Stich et al, 2003(Stich et al, , 2006Fernández-Ibáñez et al, 2007).…”

Tsunami hazard at the Western Mediterranean Spanish coast from seismic sources

“…The active deformation of the area is caused by the North-NorthWestward motion of the African plate towards the Eurasian plate, taking the latter as fixed. The rate of motion is 4-6 mm/yr (DeMets et al, 1990;McClusky et al, 2003;Serpelloni et al, 2007). This motion is accommodated here by a system of thrusts and folds striking NE-SW to E-W, with a double vergence, towards the South-East and towards the North-West.…”

“…Two families of conjugate strike-slip fault systems are active in the Alboran Basin. The main branches of this conjugate system are the left-lateral system that runs from Almeria in South-Eastern Spain towards El Jebha in Northern Morocco, known as the Trans-Alboran Shear Zone (TASZ) (Larouzière et al, 1988;Fernández-Ibáñez et al, 2007); and the right-lateral that runs from Northern Algeria towards Malaga in Southern Spain. The NE-SW trending structures have been described as transpressive, being mainly left-lateral with dip-slip reverse component (Bourgois et al, 1992;Watts et al, 1993;Martínez-Díaz, 2002;Masana et al, 2004;Booth-Rea et al, 2004;Gràcia et al, 2006), while the WNW-ESE structures are mainly right-lateral presenting normal dip-slip component in some areas (Álvarez-Marrón, 1999).…”