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The SW Iberian margin host the present-day convergent plate boundary between Iberia and Nubia. Regional seismic activity is characterized by low to moderate events, although large historical and instrumental earthquakes (Mw>8.0) have been occurred, such as the 1755 Lisbon and 1969 Horseshoe ones. The NW-SE convergence (4-5 mm/yr) is accommodated by thrusts and a set of strike-slip faults that conforms a 600 km-long and 300 km-wide deformation band named the SWIM Fault Zone. The seismogenic Lineament South (LS), a WNW-ESE 350 km-long dextral strike-slip fault, is the most prominent among them and represents an important tsunami hazard for the SW Iberian coasts due to its extension, orientation and proximity to the coast. In this work we show multi-scale seismic profiles across the LS that reveal the Plio-Quaternary activity of the fault. The LS cuts and displaces the entire sedimentary sequence up to the seafloor, generating a set of continuous crest-and-troughs of hundreds of meters wide over the seafloor. Ultra-high resolution bathymetry acquired with AUV along two 15 km-long segments of the LS shows the presence of pull-apart basins, pressure ridges, semi-circular escarpments interpreted as collapsed structures, sedimentary features such as submarine dunes with lengths ranging from 200 m to 6 km, large longitudinal erosive bed-forms interpreted as furrows, and mass movement scars

The NW-SE convergence (4-5 mm/yr) between the African and Eurasian plates controls the present-day crustal deformation in the Alboran Sea (westernmost Mediterranean). Although instrumental seismicity is characterized by low to moderate magnitude events, large earthquakes (I > IX and M > 6.0) have occurred in this region (i.e., 1522 Almeria, 1790 Oran, 1910 Adra, or 2016 Al-Idrissi earthquakes). The dextral strike-slip Yusuf Fault System (YFS) is one of the largest active faults in the Alboran Sea and its seismogenic and tsunamigenic hazard needs to be characterized. The fault system trends WNW-ESE and has a length of ~150 km. Using multi-scale bathymetric data and different morphological analysis tools (i.e., slope or relief image maps), we have characterize the changes in the morphology of the seafloor along the YFS related to its Plio-Quaternary activity. The tectonic evolution of the fault system has resulted in the formation of a large pull-apart basin, which is deeper than the surrounding areas, a topographic ridge, an elongated depression and morphologic lineaments following its trend. The dataset also images several submarine landslides scars, mainly on the steeper slopes surrounding the pull-apart basin. In addition, the analysis of ultra-high resolution bathymetry acquired with AUV has revealed the presence of a series of en-echelon scarps with heights ranging from few centimeters to less than 10 meter. Seismic profiles across these scarps show that they are related to different fault strands of the YFS that are offsetting the seafloor, possibly because of an earthquake occurred in historical times

Active fault systems accommodating relatively slow deformation still produce moderate to large magnitude earthquakes, such as those in the Alboran Sea, a Neogene basin that absorbs most of the convergence between the Eurasian and Nubian plates (4-5 mm/ year) in the westernmost Mediterranean Sea (i.e., the Almeria 1522 IEMS98 VIII-IX or the Al-Idrissi 2016 Mw 6.4 earthquakes). Accurate characterisations of how fault segments grow and connect are crucial to better understand tectonic regional processes in this and other regions with slow deformation. We characterise the North-South fault system, which currently evolves due to the transtensional stress field in the northern Alboran Sea, by means of new geomorphologic analyses grounded on quantitative relief-processing methods applied over ultra-high-resolution data acquired by AUV. We modify the Red Relief Image Maps (RRIM, Chiba et al., 2008) with our own new, specific visualisation approach, Red-Blue Relief. This method displays relief accurately and without lighting bias and presents multiscale capabilities that allows coupling with seismic data at adequate scale. As a result, we identify several seafloor morphologies as scarps, pockmarks, horst, and grabens better than previous efforts. Combining the seafloor morphology analyses with high-resolution seismic profiles across the study area, we related morphologic scarps to different normal faults. Concluding, the high segmentation of the N-S fault system and its small cumulative fault displacements suggest that this is an active system presently growing

[EN] The western Mediterranean hosts the plate boundary between the Eurasian and Nubian plates. These plates have a NW-SE convergence of 4.5 mm/year that currently controls the active deformation of the marine basins. In the westernmost basin, the Alboran Basin, the plate boundary has traditionally been understood as a zone of diffuse deformation in which there is no major structure accommodating most of the convergence. However, studies of the deep basin structure with multichannel seismic data reveal that the main submarine fault system in this basin, formed by the Alboran Ridge frontal thrust and the Yusuf strike-slip fault, accommodates at least half of the total plate convergence since the Miocene-Pliocene boundary, when they began their activity. This result challenges the diffuse deformation model, and has major implications for the assessment of the seismic and tsunamigenic hazard in the coastal areas, [ES] En el Mediterráneo occidental se encuentra el límite de placas entre las placas Eurasia y Nubia. Estas placas tienen una convergencia NO-SE de 4,5 mm/año, que actualmente controla la deformación activa de las cuencas marinas. En la cuenca más occidental, la cuenca de Alborán, el límite de placas tradicionalmente se ha entendido como una zona de deformación difusa en la que no había una estructura principal acomodando la deformación. Sin embargo, el estudio de la estructura profunda de la cuenca con datos de sísmica multicanal revelan que el principal sistema de fallas submarino en esta cuenca, formado por el frente de cabalgamiento del Alboran Ridge y la falla en dirección de Yusuf, acomoda un deslizamiento total superior a la mitad de la convergencia de placas desde el límite Mioceno-Plioceno, cuando comenzaron su actividad. Este resultado contradice el modelo de deformación difusa, y tiene grandes implicaciones para el análisis de riesgo sísmico y tsunamigénico de las zonas costeras

[EN] A key element in assessing the hazards associated with moderate to high seismic activity is the growth and connections of fault segments. The Alboran Sea is a Neogene basin located in the westernmost Mediterranean Sea and accomodate most of the convergence between the Eurasian and Nubian plates (4 – 5 mm/year) through different fault systems. This study shows the surface and depth characterization of the North-South Fault System in the northern Alboran Sea to understand better the region’s kinematics using ultra-high-resolution geophysical data acquired in the area. The data analyses have revealed the presence of several fault scarps striking N-S, resulting in horst and graben systems and the presence of pockmarks in the area. The identified faults cut the post-Messinian seismostratigraphic units (last 5.3 Ma) up to the seafloor, which supports that the fault system is currently active. Moreover, results suggest that this fault system presents high segmentation and small accumulated displacements supporting that it is in its initial evolution stage of a transtensional system, [ES] Un elemento clave a la hora de evaluar los riesgos asociados a una actividad sísmica de moderada a alta es el crecimiento y las conexiones de los segmentos de falla. El mar de Alborán es una cuenca Neógena, situada en el extremo occidental del Mediterráneo, y absorbe la mayor parte de la convergencia entre las placas Euroasiática y Nubia (4 - 5 mm/año) a través de diferentes sistemas de fallas. Este estudio muestra la caracterización en superficie y en profundidad del sistema de fallas Norte-Sur en el norte del Mar de Alborán para comprender mejor la cinemática de la región utilizando datos geofísicos de ultra alta resolución adquiridos en la zona. Los análisis de los datos han revelado la presencia de varias escarpas de fallas con dirección N-S, que dan lugar a sistemas de horst y graben y a la presencia de marcas de viruela en la zona. Las fallas identificadas cortan las unidades sismoestratigráficas post-mesinianas (últimos 5,3 Ma) hasta el fondo del mar, lo que apoya que el sistema de fallas está actualmente activo. Además, los resultados sugieren que este sistema de fallas presenta una alta segmentación y pequeños desplazamientos acumulados que apoyan que se encuentra en su etapa inicial de evolución de un sistema transtensional

[EN] The southwest Iberia margin hosted the 1755 Lisbon earthquake and ensuing tsunami, one of the most destructive natural events in European history. Here we present a plausible source and mechanism responsible for this event combining geophysical data and numerical tsunami modelling. Our results show that an intra-plate, lithospheric-scale thrust fault located at the Horseshoe Abyssal Plain coincides with the location and focal mechanisms of the largest regional earthquakes and is likely to have suitable dimensions and fault-rock properties to account for the magnitude of the 1755 event. The tsunami simulations with the Horseshoe Abyssal plain Thrust as the source reproduce reported tsunami energy propagation patterns, arrival-times and run up heights more successfully than any other proposed source, [ES] El margen suroeste de Iberia es la región donde ocurrió el terremoto de Lisboa de 1755 y el posterior tsunami, uno de los eventos naturales más destructivos de la historia europea. Aquí presentamos una fuente plausible y un mecanismo responsable de este evento que combina datos geofísicos y modelos numéricos de tsunamis. Nuestros resultados muestran que un cabalgamiento de escala litosférica intraplaca ubicado en la llanura abisal de Horseshoe coincide con la ubicación y los mecanismos focales de los terremotos instrumentales más grandes ocurridos en la región, y es probable que tenga las dimensiones y propiedades de roca de falla adecuadas para explicar la magnitud del evento de 1755. Las simulaciones de tsunami con el Horseshoe Abyssal Plain Thrust como fuente reproducen los patrones de propagación de la energía del tsunami, los tiempos de llegada y las alturas máximas de ola con más éxito que cualquier otra fuente propuesta

The Alboran Basin is located in the westernmost Mediterranean Sea. This basin was formed during the Miocene, and since the late Miocene, has been deformed due to the Iberia – Africa tectonic plates convergence, producing the contractive reorganization of some structures at the basin. Thus, the Alboran Basin is a seismically active area, which hosts the plate boundary between the European and African tectonic plates. This plate boundary has been traditionally considered a wide deformation zone, in which several small faults are accommodating the deformation. Based on a modern set of active seismic data, we were able for the first time to quantify the total slip accommodated by the most prominent tectonic structures of the area, late Miocene - early Pliocene in age. Our results show that the estimated total slip accommodated by the main fault systems may be similar (with error bounds) to the estimated plate convergence value since the Messinian time (~24 km). Thus, slip on that faults may have accommodated most of the Iberian – African plate convergence during the Plio-Quaternary, revealing that the contractive reorganization of the Alboran basin is focused on a few first-order structures that act as lithospheric boundaries, rather than widespread and diffuse along the entire basin. These results have implications not only for kinematic and geodynamic models, but also for seismic and tsunami hazard assessments. Using the most complete dataset until the date, we performed a revision of the geometry and characteristics of the main fault systems offshore. Based on this data, we perform a first appraisal of the seismogenic and tsunamigenic potential of the main fault systems offshore. Our simulations show that the seismogenic and tsunamigenic potential of the offshore structures of the Alboran Basin may be underestimated, and a further characterization of their associated hazard is needed

How fault segments grow and connect in regions with moderate to high seismic activity is key to assess associated hazards. Earthquakes may affect populated areas and can trigger tsunamis that threaten coastal areas and affect marine infrastructures. Regions accommodating relatively slow tectonic deformation may still enclose active fault systems capable of generating moderate to large magnitude earthquakes, albeit at long recurrence intervals (103 to 104 years). Although the Alboran Sea is currently characterised by slow tectonic deformation and by earthquakes of low to moderate magnitude, large historical and instrumental events have also occurred (i.e., the Almeria 1522 IEMS98 VIII-IX or the Al-Idrissi 2016 Mw 6.4 earthquakes). This Neogene basin located in the westernmost Mediterranean Sea absorbs most of the convergence between the Eurasian and Nubian plates (3 - 5 mm/year) by means of four tectonic-scale fault systems: the Carboneras and Al-Idrissi left-lateral strike-slip faults, the Yusuf right-lateral strike-slip fault and the Alboran Ridge thrust. Our study characterises the North-South fault system on the northern Alboran Sea to better understand the kinematics of the region on a larger scale. This system is proposed as the northern termination of the Al-Idrissi fault, and it may be presently evolving due to the transtensional stress field that affects the area. The first step to characterise the fault system has been to elaborate a detailed geomorphological map of the area to describe the identified scarps, their distribution, and structural relations. To achieve this, we have used very high-resolution bathymetric data (1x1 m pixel resolution) acquired with an autonomous underwater vehicle. The bathymetry shows several fault scarps striking N-S, resulting in horst and graben systems. The second step has involved the interpretation of high-resolution multichannel airgun and sparker seismic profiles running across the N-S faults. The integration of this dat

The Alboran Basin is located in the westernmost Mediterranean Sea. This basin was formed during the Miocene, and since the late Miocene, has been deformed due to the Iberia – Africa tectonic plates convergence, producing the contractive reorganization of some structures at the basin. Thus, the Alboran Basin is a seismically active area, which hosts the plate boundary between the European and African tectonic plates. This plate boundary has been traditionally considered a wide deformation zone, in which several small faults are accommodating the deformation. Based on a modern set of active seismic data, we were able for the first time to quantify the total slip accommodated by the most prominent tectonic structures of the area, late Miocene - early Pliocene in age. Our results show that the estimated total slip accommodated by the main fault systems may be similar (with error bounds) to the estimated plate convergence value since the Messinian time (~24 km). Thus, slip on that faults may have accommodated most of the Iberian – African plate convergence during the Plio-Quaternary, revealing that the contractive reorganization of the Alboran basin is focused on a few first-order structures that act as lithospheric boundaries, rather than widespread and diffuse along the entire basin. These results have implications not only for kinematic and geodynamic models, but also for seismic and tsunami hazard assessments. Using the most complete dataset until the date, we performed a revision of the geometry and characteristics of the main fault systems offshore. Based on this data, we perform a first appraisal of the seismogenic and tsunamigenic potential of the main fault systems offshore. Our simulations show that the seismogenic and tsunamigenic potential of the offshore structures of the Alboran Basin may be underestimated, and a further characterization of their associated hazard is needed

The identification and seismic characterization of the active structures in the Alboran Sea (westernmost Mediterranean) are essential to evaluate better the exposure of the South Iberian Peninsula and Maghreb coasts to different natural hazards. The Alboran Sea accommodates part of the present-day crustal deformation related to the NW-SE convergence (4-5 mm/yr) between the African and Eurasian plates. The area is characterized by low to moderate magnitude instrumental seismicity. However, large earthquakes (I > IX and M > 6.0) have occurred in this region in historical and recent times (i.e., 1522 Almeria, 1790 Oran, 1910 Adra, 1994 and 2004 Al-Hoceima or 2016 Al-Idrissi earthquakes). The dextral strike-slip Yusuf Fault System (YFS) is one of the largest active faults in the Alboran Sea and its seismogenic and tsunamigenic hazard needs to be characterized. The fault system trends WNW-ESE and has a length of ~150 km. Using multi-scale bathymetric (ranging from m to cm) and seismic data and different morphological and seismic analysis tools (i.e., slope or relief image maps), we have imaged and characterized the fault system. The analysis of this dataset reveals that the YFS is a complex structure composed of an array of strike-slip faults. The 3D structural model shows that most of the identified faults reach up and offset the seafloor and the Upper Quaternary sedimentary units. The current morphology of the seafloor is a consequence of the Plio-Quaternary tectonic evolution that have resulted in the formation of a large pull-apart basin, which is deeper than the surrounding areas, a topographic ridge, an elongated depression and morphologic lineaments following its trend. The dataset also images several submarine landslides scars, mainly on the steeper slopes surrounding the pull-apart basin. In addition, the analysis of ultra-high resolution data acquired along the Yusuf lineament with AUV has revealed the presence of a series of en-echelon scarps with heights rang

The current diffuse-strain model of the collision between Africa and Eurasia in the western Mediterranean predicts a broad region with deformation distributed among numerous faults and moderate-magnitude seismicity. However, the model is untested because most deformation occurs underwater, at poorly characterized faults of undetermined slip. Here we assess the diffuse-strain model analysing two active offshore fault systems associated with the most prominent seafloor relief in the region. We use pre-stack depth migrated seismic images to estimate, for the first time, the total Plio-Holocene slip of the right-lateral Yusuf and reverse Alboran Ridge structurally linked fault system. We show that kinematic restoration of deformational structures predicts a slip of 16 ± 4.7 km for the Alboran Ridge Fault and a minimum of 12 km for the Yusuf Fault. Thus, this fault system forms a well-defined narrow plate boundary that has absorbed most of the 24 ± 5 km Plio-Holocene Africa-Eurasia convergence and represents an underappreciated hazard

Cold-water corals are key species of benthic ecosystems, sensitive to changes in climate and capable of recording them in the chemical composition of their skeletons. The study of cold-water coral mound development in relation to palaeoceanographic variations during the Pleistocene and Holocene stages in the Mediterranean Sea has mainly been focussed in the Alboran Sea (Western Mediterranean). The present study describes the coral deposits and corresponding ages of 3 gravity cores, acquired from the newly discovered Tunisian Coral Mound Province (Central Mediterranean), which comprises several ridge-like mounds. All the cores acquired displayed dense coral deposits, dominated by Desmophyllum pertusum fragments embedded within a muddy sediment matrix. Overall, 64 coral samples have been dated with the Usingle bondTh laser ablation MC-ICP-MS method, revealing corals of mostly Pleistocene age ranging from ~MIS 11 to 8.4 ka BP. Although coral mound formation was reduced for most of the last 400 kyr, a main stage of pronounced mound formation occurred during the last glacial period, which contrasts to the findings previously published for coral mounds in other regions of the Mediterranean Sea. Coral mound formation during the last glacial was most likely associated with a colder seawater temperature than the one observed in the present-day, an increased surface productivity and an appropriate depth of the interface between Atlantic Waters and Levantine Intermediate Waters. The combination of the data acquired here with that of previous mound formation studies from the Alboran Sea also suggests that cold-water coral mounds located at greater depths develop at slower rates than those found in shallower settings

Us presentem vint-i-cinc investigadores que estan desenvolupant projectes punters en els camps de la ciència i la tecnologia a casa nostra

A poorly defined boundary between the Nubia and Eurasian plates runs along the Northern Tunisian continental margin. The Tunisia margin is deformed by a slow NW–SE trending convergence resulting in a diffuse deformation zone with scarce and scattered seismicity compared to the seismic activity into the neighboring regions to the east and west along the boundary. The area has been poorly studied and therefore its recent evolution is almost unknown, particularly offshore. Here, we present a structural analysis of the active tectonics in this submarine continental margin. The data used for this analysis are high-resolution bathymetric maps together with parametric echosounder images which have allowed to obtain a map of active faulting with unprecedented detail. The structural analysis supports a dominantly transpressive to compressive component of faulting, resulting from the current regional NW–SE trending compressive regime between plates. The North-eastern Domain of the study region contains the highest number of active faults with numerous pockmarks aligned along them. This study shows that the plate boundary across the North Tunisia margin is incipient and poorly developed, which may be due to the fact that deformation is partitioned over a large number of structures, each accommodating a small percentage of convergence, with the exception of the Hayat fault system. The Hayat reverse fault, striking WSW–ENE, is the largest fault system that comparatively may accommodate a greater amount of displacement, and is probably responsible for the uplift of the North-eastern Domain of the continental margin

The westernmost Mediterranean hosts part of the plate boundary between the European and African tectonic plates. Based on the scattered instrumental seismicity, this boundary has been traditionally interpreted as a wide zone of diffuse deformation. However, recent seismic images and seafloor mapping studies support that most of the plate convergence may be accommodated in a few tectonic structures, rather than in a broad region. Historical earthquakes with magnitudes Mw > 6 and historical tsunamis support that the low-to-moderate instrumental seismicity might also have led to underestimation of the seismogenic and tsunamigenic potential of the area. We evaluate the largest active faults of the westernmost Mediterranean: the reverse Alboran Ridge, and the strike-slip Carboneras, Yusuf and Al-Idrissi fault systems. For the first time, we use a dense grid of modern seismic data to characterize the entire dimensions of the main fault systems, accurately describe the geometry of these structures and estimate their seismic source parameters. Tsunami scenarios have been tested based on 3D-surfaces and seismic source parameters, using both uniform and heterogeneous slip distributions. The comparison of our results with previous studies, based on limited information on the fault geometry and kinematics, indicates that accurate fault geometries and heterogeneous slip distributions are needed to properly assess the seismic and tsunamigenic potential in this area. Based on fault scaling relations, the four fault systems have a large seismogenic potential, being able to generate earthquakes with Mw > 7. The reverse Alboran Ridge Fault System has the largest tsunamigenic potential, being able to generate a tsunami wave amplitude greater than 3 m in front of the coasts of Southern Spain and Northern Africa