Active faulting and earthquakes in the central Alboran Sea

Central Alboran Sea constitutes a key area to analyze the relationships between active tectonic structures and moderate seismicity. The heterogeneous crustal layered structure and the propagation of the deformation along the fault zones are key features to relate active faults and seismic hazard. The NW-SE oblique convergence between Eurasian and African plates determines the broad band of tectonic deformation and seismicity along the Alboran Sea basin (westernmost Mediterranean). The Betic-Rif Cordilleras are connected through the Gibraltar Arc and surround the Alboran Sea formed by thinned continental crust. This basin is filled since the Neogene by sedimentary and volcanic rocks. Central Alboran Sea is now undergoing shortening and is mainly deformed by a system of conjugated WNW-ESE dextral and NE-SW sinistral faults with recent activity formed by indenter tectonics related to a heterogeneous crustal behavior. In addition a NNW-SSE normal fault set and large ENE-WSW folds deform the central and northern Alboran Sea. These structures support a present-day N160 E maximum compression and orthogonal extension. In this setting, most of the recent seismicity is concentrated along a NNE-SSW zone that extends landward from Campo de Dalias (SE Spain) to Al Hoceima (Morocco). The Campo de Dalias 1993-1994 seismic crisis reached up to magnitudes Mw= 5.3, while the Al Hoceima area was affected by seismic crisis of 1994 (May 26, Mw=5.6) and 2004 (Feb 24, Mw= 6.4). The main active fault related to the 2004 earthquakes, even that it was a vertical NNE-SSW oriented fault and focal depth was 6 km, did not reach the surface probably due to the presence of a mechanically layered crust. The main active surface faults located in Al Hoceima area (the NNE-SSW transtensional sinistral Trougout fault zone) extended northwards towards the NE-SW sinistral Al Idrissi Fault that intersects the Alboran Sea and are connected with the normal NNW-SSE Balanegra Fault zone. Although these active faults determine most of the seismicity of the central Alboran Sea, the seismic crisis that occurred since January 2016, reaching Mw= 6.3 is located in a region westward of Al Idrissi Fault, underlining the relevance of growth of new faults to determine the seismic hazard of the region. Earthquake focal mechanisms support that the main active fault has a NNE-SSW orientation, similar to Al Idrissi Fault zone. Maximum magnitude suggests a surface rupture length of at least 12 km and a subsurface rupture of 20 km. Propagation of a new fault is more efficient to accumulate elastic deformation, and to produce highest magnitude earthquakes than already formed faults. This new fault is connected probably in deep crustal levels with the blind sinistral fault responsible of the 2004 Al Hoceima earthquake. The tsunami hazard of the region should be consequence of both seabottom displacement due to fault activity and co-seismic submarine landslides. The INCRISIS cruise, scheduled by May 2016, will provide evidences of seabottom effects of this seismic crisis

Contourite depositional system after the exit of a strait: Case study from the late Miocene South Rifian Corridor, Morocco

Idealized facies of bottom current deposits (contourites) have been established for fine-grained contourite drifts in modern deep-marine sedimentary environments. Their equivalent facies in the ancient record however are only scarcely recognized due to the weathered nature of most fine-grained deposits in outcrop. Facies related to the erosional elements (i.e. contourite channels) of contourite depositional systems have not yet been properly established and related deposits in outcrop appear non-existent. To better understand the sedimentary facies and facies sequences of contourites, the upper Miocene contourite depositional systems of the South Rifian Corridor (Morocco) is investigated. This contourite depositional system formed by the dense palaeo-Mediterranean Outflow Water. Foraminifera assemblages were used for age-constraints (7.51 to 7.35 Ma) and to determine the continental slope depositional domains. Nine sedimentary facies have been recognized based on lithology, grain-size, sedimentary structures and biogenic structures. These facies were subsequently grouped into five facies associations related to the main interpreted depositional processes (hemipelagic settling, contour currents and gravity flows). The vertical sedimentary facies succession records the tectonically induced, southward migration of the contourite depositional systems and the intermittent behaviour of the palaeo-Mediterranean Outflow Water, which is mainly driven by precession and millennial-scale climate variations. Tides substantially modulated the palaeo-Mediterranean Outflow Water on a sub-annual scale. This work shows exceptional examples of muddy and sandy contourite deposits in outcrop by which a facies distribution model from the proximal continental slope, the contourite channel to its adjacent contourite drift, is proposed. This model serves as a reference for contourite recognition both in modern environments and the ancient record. Furthermore, by establishing the hydrodynamics of overflow behaviour a framework is provided that improves process-based interpretation of deep-water bottom current deposits

The late Ollgocene-early BurdigaHan extensional stages in the Ghomarides nappes (internai Rif, Morocco)

The Ghomarides nappes are overlain by late OUgocene-eariy Burdigaiian moiassic deposits. These deposits show three successive extensional stages wich are oriented: 1- NE-SW during late Oligocene. 2- NW-SE duringAquitanian. 3- ENE-WSW during the early BurdigaiianLes nappes Ghomarides du Rif interne sont recouvertes par des dépôts post-nappes d'âge oligocène supérieur-burdigaHen inférieur. Ces dépôts, à caractères moiassiques, montrent des failles normales appartenant à trois épisodes estensifs: 7- NE-SW d'âge fin-Oiigocène. 2- NW-SE d'âge Aquitanien. 3- ENE-WSW d'âge burdigalien inférieu

Comment on "Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin: The Tanger-Ketama Unit (external Rif, northern Morocco)" by Vázquez et al., Geologica Acta 11 (2013), 277-293

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Geodynamics of the Gibraltar Arc and the Alboran Sea region

International audienceLocated at the Westernmost tip of the Mediterranean sea, the Gibraltar Arc is a very complex zone. The Betics in Spain and the Rif belt in Morocco surround the Alboran sea characterized by a thinned continental crust. The geodynamic evolution of this region results from the convergence of African and Iberian margins since the Late Cretaceous. It is controlled both by plate convergence and mantle dynamics, which significantly impact on morphology, sedimentary environments, tectonics, metamorphism and magmatism. We present here the contents of the special issue on the Gibraltar Arc and nearby regions, following the workshop organized at the University Abdelmalek Essaadi of Tetouan in Morocco from 27 to 28 October, 2011. The goal of this international workshop was to have an overview of the actual advance in research concerning the Rif and Betics chains, the Alboran basin, and their influence on the Iberian and African forelands

Kinematics and paleostresses in the Jebha-Chrafate transcurrent fault (northern Rif, Morocco)

4 páginas, 3 figuras.-- Trabajo presentado en la 38ª Sesión Científica, Teruel, 2005.The Jebha-Chrafate is an ENE-WSW sinistral major transcurrent fault of the Rif Cordillera, formed during the southwestwards emplacement of the Internal Zones on the Flysch units and the External Zones. The analysis of minor structures along the Jebha area indicates the activity of top to the SW low and high angle normal faults during the tectonic wedge emplacement. In addition, most of the kinematic indicators along the transcurrent fault zone point to a reactivation as dextral fault during the recent NW-SE Eurasia-Africa convergence and a final overprinting of normal faults during the late stages of relief uplift.Este trabajo se ha realizado gracias a la beca postdoctoral concedida al primer firmante por parte de la Agencia Española de la Cooperación Internacional (AECI) 2004-2005. El trabajo ha sido financiado por proyectos de la Consejería de Presidencia (Junta de Andalucia), AECI y BTE 2003-01699 (CICyT).Peer reviewe