Seafloor Morphology and Processes in the Alboran Sea

The seafloor of the Alboran Sea reflects its complex tectonic, sedimentary, and oceanography dynamics as a consequence of the geological context, involving interaction between the Eurasian and African plates, and oceanographic context, as it is where the Atlantic and Mediterranean waters meet. Their physiography has a semi-enclosed configuration characterized by two margins (the Spanish Iberian and North Africa—mostly Moroccan margins) enclosing deep basins. Tectonic activity is mainly attested by folds and faults that predominantly affect the central and eastern seafloor sectors, as well as numerous seamounts and fluid-flow features (pockmarks, mud volcanoes, and diapirs) that dot the seafloor. The sedimentary and oceanographic processes allow us to distinctly define two principal environments in the Alboran Sea: the shallow proximal margin (continental shelf); and the deep distal margin (continental slope and base of the slope) with the adjacent sub-basins. The shelf mostly comprises prodeltaic and infralittoral prograding wedges, with local bedform fields, submarine valleys, and wave-cut terraces. Coastal and fluvio-marine sedimentary processes, acting since the last glacial period, are responsible for these features. The deep marine environment is characterised by the ubiquity of contourites, whose continuity is interrupted by turbidite systems, canyons, and landslides. The alongslope action of the Mediterranean waters and their interfaces with the Atlantic water has been the main process governing transport, seafloor reworking, and sedimentation of contourites. Mass-movement processes are responsible for the formation of: (1) turbidite systems—turbidity flows and mass flows were dominant during the last glacial sea-level lowstand, evolving to dilute gravity flows during present interglacial high stand; and (2) landslides—the main triggering factors comprising over-steepening, seismicity, under consolidation due to overpressure by interstitial fluids, stratigraphy, and high sedimentation rates. Locally, still-undetermined biological activity in the Spanish and coral activity in the Moroccan margin generated fields of mounded bioconstructions. The seafloor morphology of the Alboran Sea offers interesting clues for assessing the main potential geological hazards, with tectonic seismicity and landslides (as well as their related tsunamis) being some of the most important potential hazards affecting coastal populations. In addition, the seafloor morphology in combination with assemblages of habitat-forming species enables habitat identification and mapping.En prens

Use of Active Fault Data versus Seismicity Data in the Evaluation of Seismic Hazard in the Granada Basin (Southern Spain).

9 páginas, 5 figuras, 2 tablas.In this article we evaluate the seismic hazard in the Granada Basin (southern Spain), using for the first time the slip rate of known active faults. Our study, as an attempt to compute seismic hazard using active fault data in low to moderate seismicity regions, relies on a complete database of these faults containing information relevant to their seismic potential. We obtain peak ground acceleration values above 0.4g for a return period of 475 years. This result is compared with previous evaluations carried out on the basis of the historical seismicity of the area and the application of the well-known theorem of total probability. In these cases, maximum values of 0.2g are obtained. We explain the discrepancies found between the slip rate-derived and seismicity-derived estimates of seismic hazard as owing to the different strikes of the faults in relation to the directions of the main stresses affecting the Granada Basin, in the context of the Betic Cordilleras, some of them with evidence of aseismic slip.Peer reviewe

Seismic potential of faults in the Granada Basin (Betic Cordillera, Spain)

6 páginas, 2 figuras, 1 tabla.-- Trabajo presentado en Proceedings of the 9º Congress, Athens, Septiembre 2001.A fault datbase has been created for the Granada basin ( S. Sapin) concernig seismic potential in this area,. The fault lines have been entered as well as their geometry and displacement rate, when known from accumulated displacement. empirical relationships have been used between the lenght or surface of the faults and the estimates for displacements during earthquakes.Peer reviewe

Seismic Potential of the Main Active Faults in the Granada Basin (Southern Spain)

20 páginas, 5 figuras, 1 tabla.The main active faults of the Granada Basin are located in its central-eastern sector, where the most important tectonic activity is concentrated, uplifting its eastern part and sinking the western border. Several parameters related to the seismic potentiality of these active, or in some cases probably active, faults in this basin are used for the first time. Many of these faults can generate earthquakes with magnitudes larger than 6.0 MW, although this is not the general case. The fault situated to the N of Sierra Tejeda, probably the one responsible for the big earthquake of 25/12/1884, stands out, because it could generate an earthquake with magnitude 6.9 MW. Although at present all the data needed are not fully known, we consider that the final results show, as a whole, the average expected return periods of the faults in the Granada Basin.This article was funded by projects PB97-1267-C03-01 and REN2000-0777-C02- 01 RIES of the DGICYT and the group RNM 0217 of the Junta de Andalucía.Peer reviewe

Deployment of a local semi-permanent seismic network along the northern Guadiana Menor River area (Betic Cordillera)

Congreso realizado en Toledo del 28 de noviembre al 1 de diciembre de 2022.[EN] In the last decade, the Guadiana Menor River region, in the Guadalquivir foreland Basin, has suffered some low to moderate magnitude seismic sequences. For instance, the 2012-2013 Sabiote-Torreperogil seismic sequence, 1 to 5 km deep, being the biggest recorded event a mbLg 3.9, and the 2016-2018 Jódar-Peal de Becerro seismic sequence, less than 2 km and other events at 9 to 13 km deep, located 20 km southeast of the previous one, being a mbLg 4.1 earthquake the greatest recorded magnitude. In the last years, the Spanish IGN national seismic network has also recorded several low magnitude earthquakes in the region, clearly showing that the fault that hosted the 2016-2018 seismic sequence continues to be active.This has been the reason to deploy a local seismic network in the region, designed with the aim to study this persistent seismicity in terms of both locations and focal mechanism solutions. It is equipped with seven triaxial broadband sensors, also sharing data coming from two nearby IGN seismic stations. Most of them are recording data from September 2021. Real-time records are shared with the Spanish IGN seismic network in order to improve regional locations.Peer reviewe

Tsunamigenic risk associated to vertical offset in transcurrent fault termination (Westernmost Mediterranean)

European Geosciences Union (EGU) General Assembly, 7-12 April 2019, Vienna, Austria.-- 1 pageThe Mediterranean Sea has one of the longest records of tsunami and represents the 10.1 percentage distribution of tsunami in the world’s oceans and seas. The Alboran Basin (Westernmost Mediterranean) is tectonically active as it is suggested by recent earthquakes triggered by several faults, mostly located in the central zone, and formed due to the tectonic indentation in a context of convergence between Africa and Eurasia plates. One of these active faults is the Averroes fault, a NW-SE dextral transcurrent structure with vertical offset at its termination, which is analysed to test its tsunamigenic potentiality. While the propagation of tsunamis by normal or reverse faults is well simulated by numerical models, those generated by structures as the Averroes fault, has not received the interest of the scientific community attention. Through a multidisciplinary approach that involves morphological, seismic stratigraphy, and physical and numerical modellings, we test the generation of tsunamis or the subsequent inundation by the Averroes fault. The bathymetric and seismic analysis point to the Averroes fault has a maximum vertical offset of 5.4 m. The crustal deformation at the sea bottom surface generated by a given earthquake hosted in the Averroes Fault has been computed using the Coulomb 3.3 code, where calculations are done using the Okada’s 1992 approach, assuming an elastic halfspace with uniform elastic properties. Computed deformation pattern is characterized by an uplifting lobe (footwall block) and a subsiding lobe (hanging wall block). The Mw for this event is 7.03. The tsunami wave propagation generated by the seafloor deformation has been modelized with the Tsunami-HySEA (HySEA stands for Hyperbolic Systems and Efficient Algorithms). The tsunami modelling shows three main wave fronts directed towards the NW, NE and S, being the most affected areas the Campo de Dalias (Almeria) and Malaga, located to the north of the Averroes Fault in the Spanish coast. The maximum wave heights reach about 3 m in the Averroes fault area, and about 2.5 m in the Campo de Daliasand Malaga coasts. The time arrivals are 15’ for the first case and about 25’ for the last.The results of this work contribute to increase the number of tsunamigenic sources to be considered in the Alboran Sea. Although transcurrent structures have not been considered by their kinematics as potential triggers of tsunamis, here we demonstrate that the vertical offset at their terminations may generate destructive tsunamis. In addition, in the case of the Alboran Sea, those tsunamis would represent rapid-onset hazards, with time arrivals too short for alert systems, in a densely populated coast that increases during tourist arrivals during the spring and summer periods. This study also highlights the need to review the tsunamigenic potential hazards for similar strike-slip faults with vertical offsets in other seas and ocean