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During the TSUJAL marine geophysical survey, conducted in February and March 2014, Spanish, Mexican and British scientists and technicians explored the western margin of Mexico, considered one of the most active seismic zones in America. This work aims to characterize the internal structure of the subduction zone of the Rivera plate beneath the North American plate in the offshore part of the Jalisco Block, to link the geodynamic and the recent tectonic deformation occurring there with the possible generation of tsunamis and earthquakes. For this purpose, it has been carried out acquisition, processing and geological interpretation of a multichannel seismic reflection profile running perpendicular to the margin. Crustal images show an oceanic domain, dominated by subduction–accretion along the lower slope of the margin with a subparallel sediment thickness of up to 1.6 s two-way travel time (approx. 2 km) in the Middle American Trench. Further, from these data the region appears to be prone to giant earthquake production. The top of the oceanic crust (intraplate reflector) is very well imaged. It is almost continuous along the profile with a gentle dip (<10°); however, it is disrupted by normal faulting resulting from the bending of the plate during subduction. The continental crust presents a well-developed accretionary prism consisting of highly deformed sediments with prominent slumping towards the trench that may be the result of past tsunamis. Also, a bottom simulating reflector (BSR) is identified in the first half a second (twtt) of the section. High amplitude reflections at around 7–8 s twtt clearly image a discontinuous Moho, defining a very gentle dipping subduction plane., Consejo Nacional de Ciencia y Tecnología (México), Ministerio de Economia y Competitividad (España), Universidad Nacional Autonoma de Mexico, Generalitat de Catalunya, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

Processing and analysis of new multichannel seismic records, coincident with wide-angle seismic profiles, acquired in the framework of the TsuJal project allow us to investigate in detail the complex structure of the oceanic domain in the collision zone between Rivera Plate and Block Jalisco at its northern termination. The subducting Rivera Plate, which is overridden by the North American Plate–Jalisco Block, is clearly identified up to 21.5°N (just south of Maria Magdalena Island) as a two clear reflections that we interpret as the interplate and Moho discontinuities. North of the Tres Marias Islands the seismic images display a different tectonic scenario with structures that are consistent with large faulting and rifted margin. A two-dimensional velocity approach for the crustal geometry is achieved using joint refraction/reflection travel time tomography, the uncertainty of the results is assessed by means of Monte Carlo analysis. Our results show an average oceanic crustal thickness of 6–7 km with a moderate increase towards the Jalisco Block, an anomalous thick layers (~3.0 km) displaying a relatively low velocity (~5.5 km/s) underneath Maria Magdalena Rise, and an estimated Moho depth deeper than 15 km in the collision zone between Rivera Plate and Jalisco Block. We have also determined an anomalous crust on the western flank of the Tres Marias Islands, which may be related to the initial phases of continental breakup of the Baja California Peninsula and Mexico mainland. High-resolution bathymetry provides remarkable images of intensive slope instabilities marked by relatively large slides scars of more than 40 km2 extent, and mass-wasting deposits probably triggered by the intense seismicity in the area., Consejo Nacional de Ciencia y Tecnología (CONACYT) –FOMIXJal, Gobierno de España, Gobierno del Estado de Jalisco, Universidad Nacional Autonoma de Mexico, Agencia Estatal de Investigación (España), Programa Ramón y Cajal, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

In the spring of 2014, an onshore–offshore geophysical experiment (“Crustal Characterization of the Rivera plate–Jalisco Block Boundary and Its Implications for Seismic and Tsunami Hazard Assessment”) was carried out in the frame of the TsuJal project to define the crustal architecture of the western Mexican active margin and identify potential structural sources that can trigger earthquakes and tsunamis at the convergence between the Rivera plate (RP) and the Jalisco Block (JB) within the North American plate. In this work, we present the preliminary results about bathymetric, structural geology, and wide‐angle seismic data of the southern coast of Bahía de Banderas. These data indicate the slab thickness in this area is about 10 km and presents a dip angle of about 8°. Continental crustal thickness below Puerto Vallarta is about 20 km, but no evidences of continental Moho and clear subduction features (trench, accretionary prism) are observed. Nevertheless, this model supports the hypothesis that the region of Bahía de Banderas is under strong crustal stresses generating structural lineaments with the same trends offshore and inland due to the convergence of the RP against the JB. Most of the seismicity reported can be associated with the main structural lineaments. Moreover, the Banderas Canyon (BC) is apparently in an eastward opening process, which seems to continue through the Rio Pitillal river valley; no seismic or morphological evidences were found to suggest the BC is a continuation of the Vallarta graben. Offshore, the Sierra de Cleofas, located south of María Cleofas Island, marks the limit between the RP and the JB along 100 km. It may be the result of the RP pushing against the JB establishing the beginning of the current subduction process, with associated seismic activity. If a subduction type earthquake occurs in this area, the associated magnitude will be about 7.5 and could have a tsunamigenic effect., Consejo Nacional de Ciencia y Tecnología (México), Ministerio de Economía y Competitividad (España), Depto. de Física de la Tierra y Astrofísica, TRUE, pub

By creating a dependable, transparent, and cost-effective system for forecasting and ongoing environmental impact monitoring of exploration and exploitation activities in the deep sea, TRIDENT seeks to contribute to the sustainable exploitation of seabed mineral resources. In order to operate autonomously in remote locations under harsh conditions and send real-time data to authorities in charge of granting licenses and providing oversight, this system will create and integrate new technology and innovative solutions. The efficient monitoring and inspection system that will be created will abide by national and international legal frameworks. At the sea surface, mid-water, and the bottom, TRIDENT will identify all pertinent physical, chemical, geological, and biological characteristics that must be monitored. It will also look for data gaps and suggest procedures for addressing them. These are crucial actions to take in order to produce accurate indicators of excellent environmental status, statistically robust environmental baselines, and thresholds for significant impact, allowing for the standardization of methods and tools. In order to monitor environmental parameters on mining and reference areas at representative spatial and temporal scales, the project consortium will thereafter develop and test an integrated system of stationary and mobile observatory platforms outfitted with the most recent automatic sensors and samplers. The system will incorporate high-capacity data processing pipelines able to gather, transmit, process, and display monitoring data in close to real-time to facilitate prompt actions for preventing major harm to the environment. Last but not least, it will offer systemic and technological solutions for predicting probable impacts of applying the developed monitoring and mitigation techniques

Investigadores del Instituto de Ciencias del Mar de Barcelona han desvelado la imagen sísmica más detallada de la costa noroeste del Pacífico de México en la que se han registrado hasta tres grandes terremotos tsunami génicos de magnitud ocho en los últimos 100 años

The parameters allowing for near-trench megathrust ruptures are debated and commonly involve the presence of site-dependent tectonic factors (e.g. rough subducting topography, amount of sediments), implying the need for direct geophysical observations. Here we use seismic imaging techniques to explore the mechanisms triggering shallow ruptures in the Rivera subduction zone, along the non-accretionary Jalisco-Colima continental margin, W Mexico, where three large (Mw~8) tsunamigenic megathrust earthquakes occurred in the last century. The seismic image reveals large interplate topographic variations morphologically alike to incoming trench-parallel ridges seaward of the study area. Ridge subduction only occurs along the southern non-accretionary margin of the Rivera system, where past earthquakes released large near-trench coseismic energy, indicating that subducting ridges enhance interplate coupling. Subducting ridges uplift the margin, causing upper-plate fracturing and low rigidity areas. Such elastic structure quantitatively explains the dynamics of slow and tsunamigenic ruptures in the past. We conclude that ridge subduction beneath the Jalisco-Colima continental margin promotes shallow seismogenesis and explains the large tsunamigenic potential of the area

[EN] A new study led by the ICM-CSIC explains for the first time the large occurrence of tsunamis and earthquakes in the region, [ES] Un nuevo estudio liderado por el ICM-CSIC permite explicar por primera vez la gran ocurrencia de tsunamis y terremotos en la región, [CAT] Un nou estudi liderat per l'ICM-CSIC permet explicar per primer cop la gran ocurrència de tsunamis i terratrèmols a la regió

Conceptual models of magma-poor rifting are strongly based on studies of the nature of the basement in the continent-to-ocean transition of the Iberia Abyssal Plain, and suggest that exhumed mantle abuts extended continental crust. Yet, basement has only been sampled at a few sites, and its regional nature and the transition to seafloor spreading inferred from relatively low-resolution geophysical data are inadequately constrained. This uncertainty has led to a debate about the subcontinental or seafloor-spreading origin of exhumed mantle and the rift-related or oceanic nature of magmatic crust causing the magnetic J anomaly. Different interpretations change the locus of break-up by >100 km and lead to debate of the causative processes. We present the tomographic velocity structure along a 360-km-long seismic profile centered at the J anomaly in the Iberia Abyssal Plain. Rather than delineating an excessive outpouring of magma, the J anomaly occurs over subdued basement. Furthermore, its thin crust shows the characteristic layering of oceanic crust and is juxtaposed to exhumed mantle, marking the onset of magma-starved seafloor spreading, which yields the westward limit of an ~160-km-wide continent–ocean transition zone where continental mantle has been unroofed. This zone is profoundly asymmetric with respect to its conjugate margin, suggesting that the majority of mantle exhumation occurs off Iberia. Because the J anomaly is related to the final break-up and emplacement of oceanic crust, it neither represents synrift magmatism nor defines an isochron, and hence it poorly constrains plate tectonic reconstructions.

Gas hydrates (GHs) are susceptible to climate-induced perturbations such as changes in sea level and temperature and may provide feedback to such perturbations. The occurrence of GHs in the Pacific margin of the Antarctic Peninsula (PAP) is well known from seismic data, including a Bottom Simulating Reflector (BSR). Such BSR is widespread between Elephant and King George Is in water depths between 1000-3000 m. Previous studies in the area assessed the geothermal gradient from the BSR depth (~31°C/km±3.15 MAD) assuming the GH is in equilibrium. However, nearby heat flow determinations suggest that GHs are not in equilibrium, as the derived geothermal gradient is significantly higher (~97°C/km±36.4 MAD). Thus, the BSR is 100-400 m deeper than the theoretical Base of the GH Stability Zone (BGHSZ) in the area. Overpressure resulting from rapid sedimentation or tectonic stresses cannot explain alone the observed depth of the BSR, as it cannot balance for the thermal conditions at such depths. Vertical movements of tectonic and/or glacial-isostatic origin could be only partially responsible for the mismatch between observed BSR and theoretical BGHSZ depths. Hence, a better knowledge of the thermal regime of the PAP is needed to assess the dynamics of the GH system. A research cruise in 2024 aims to constrain better the dynamics of the GH system of the PAP using geophysical imaging and heat flow measurements. The cruise will also assess the potential export of methane into the ocean using a suite of geochemical indicators in sediments, pore waters and the water column

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

Conceptual models of magma-poor rifting are strongly based on studies of the nature of the basement in the continent-to-ocean transition of the Iberia Abyssal Plain, and suggest that exhumed mantle abuts extended continental crust. Yet, basement has only been sampled at a few sites, and its regional nature and the transition to seafloor spreading inferred from relatively low-resolution geophysical data are inadequately constrained. This uncertainty has led to a debate about the subcontinental or seafloor-spreading origin of exhumed mantle and the rift-related or oceanic nature of magmatic crust causing the magnetic J anomaly. Different interpretations change the locus of break-up by >100 km and lead to debate of the causative processes. We present the tomographic velocity structure along a 360-km-long seismic profile centered at the J anomaly in the Iberia Abyssal Plain. Rather than delineating an excessive outpouring of magma, the J anomaly occurs over subdued basement. Furthermore, its thin crust shows the characteristic layering of oceanic crust and is juxtaposed to exhumed mantle, marking the onset of magma-starved seafloor spreading, which yields the westward limit of an ~160-km-wide continent–ocean transition zone where continental mantle has been unroofed. This zone is profoundly asymmetric with respect to its conjugate margin, suggesting that the majority of mantle exhumation occurs off Iberia. Because the J anomaly is related to the final break-up and emplacement of oceanic crust, it neither represents synrift magmatism nor defines an isochron, and hence it poorly constrains plate tectonic reconstructions.

[EN] According to the World Wildlife Fund for Nature (United Nations, 2015), 50% of the world’s population lives within 100 km of the coast, 16 of the world’s 23 megacities face the oceans and one billion people live in communities with direct links to the sea. The need for a safe ocean, i.e. the need to reduce marine risks and losses, is key to the future of our planet’s inhabitants. According to the Hyogo Framework for Action of the United Nations Office for Disaster Risk Reduction (UNDRR), a risk is defined as a process, phenomenon or human activity that may cause loss of life, injury or other health impacts, property damage, social and economic disruption or environmental degradation. Risks range from natural hazards (geological, climatic or biological) to those induced by human activity (accidents and environmental changes). […], [ES] Según el World Wildlife Fund for Nature (Naciones Unidas 2015) el 50% de la población mundial vive a menos de 100 km de la costa, 16 de las 23 megaciudades del mundo están frente a los océanos y 1000 millones de personas viven en comunidades con vínculos directos con el mar. La necesidad de un océano seguro, es decir, de reducir los riesgos marinos y sus pérdidas, es clave para el futuro de los habitantes de nuestro planeta. Según el Hyogo Framework for Action of the United Nations Office for Disaster Risk Reduction (UNDRR), un riesgo se define como un evento, fenómeno o actividad que puede causar pérdidas humanas, sociales, económicas o la degradación medioambiental. En riesgos se incluyen desde los naturales (geológicos, climáticos o biológicos) a los inducidos por la actividad humana (accidentes y cambios medioambientales). […], [CAT] Segons el World Wildlife Fund for Nature (Nacions Unides 2015) el 50% de la població mundial viu en la franja de costa marítima de 100 km, 16 de les 23 megaciutats del món estan davant dels oceans i 1000 milions de persones viuen en comunitats amb vincles directes amb el mar. La necessitat d’un oceà segur, és a dir, de reduir els riscos marins i les seves pèrdues, és clau per al futur dels habitants del nostre planeta. Segons el Hyogo Framework for Action of the United Nations Office for Disaster Risk Reduction (UNDRR), un risc es defineix com un esdeveniment, fenomen o activitat que pot causar pèrdues humanes, socials, econòmiques o la degradació mediambiental. Dintre dels riscos s’inclouen des dels naturals (geològics, climàtics o biològics) als induïts per l’activitat humana (accidents i canvis mediambientals). […]

[EN] Multibeam bathymetry and more than 1519 nm of very high-resolution parametric profiles (TOPAS and ParasoundP-35) were used to characterize the recent morpho-sedimentary evolution of the Garrucha canyon system located in the Palomares continental margin (SW Mediterranean). For this purpose, unconventional seismic processing was performed to improve 784 nmof the parametric profiles that presented low-quality images.Three main echo-facies, (a) stratified (b) non-penetrative and (c) transparent were distinguished, mapped and interpretedin terms of sedimentaryprocesses, allowing the identification of several depositional, erosional and mass movement features distributed in the canyon domain and its margins. Upper-slope depositional systems, including contourite drifts, are interrupted by the tributaries of the Garrucha canyon system, which in turn, exhibits a network of gullies. Mass movement features (MTD) are distributed along the margin and are identified as the dominant sedimentary features in the continental slope on the canyon margins and walls.The most likely trigger of the near-surface slope failures described is the tectonic activity and the interaction of fluvio-marine processes, [ES] La evolución morfo-sedimentaria reciente del sistema de cañón de Garrucha localizado en el margen continental de Palomares (SO Mediterráneo), ha sido caracterizada mediante datos de batimetría multihaz y perfiles paramétricos de muy alta resolución (TOPAS y Parasound P-35). Debido a la escasa calidad de una parte de los perfiles paramétricos disponibles, unas 784 millas náuticas de perfiles se han procesado mediante un procedimiento no convencional pero aplicable a datos paramétricos. El análisis de los perfiles sísmicos ha permitido definir 3 tipos de eco-facies principales:(a) estratificada, (b) no-penetrativa y (c) transparente, así como su distribución en el área de trabajo. Esto interpretado en términos de procesos sedimentarios permitió delimitar los procesos deposicionales, erosivos e inestabilidades sedimentarias como los principales que definen el sistema de cañón de Garrucha. Los elementos deposicionales como los depósitos contorníticos presentes en el talud continental superior, se ven interrumpidos por el sistema de cañón que a su vez está afectado por elementos erosivos como cárcavas. Las inestabilidades sedimentarias (MTD) son los procesos dominantes tanto en los diferentes dominios del cañón como en los márgenes. La actividad tectónica y la interacción con procesos fluvio-marinos se han identificado como los principales detonantes (triggers) de la inestabilidad sedimentaria en la zona de estudio

The 74 km long Almanzora-Alías-Garrucha canyon system is one of the most important submarine canyons located in the Palomares continental margin (SW Mediterranean Sea). The canyon head and upper course are constituted by several tributaries such as Almanzora, Garrucha, Cabrera and Alias canyons from N to S. During 3 recent oceanographic cruises, different multibeam echosounder datasets were merged and also an extensive network of parametric profiles was recorded to study the canyon. A total of 1519 nautical miles of parametric profiles (TOPAS and Parasound P-35, penetration < 150 m) were acquired in order to characterize the main morphological features and to map the eco-facies defining the deposits and sedimentary processes along the different canyon domains, included its margins. The parametric profiles have been processed after the deconvolution of the continuous 4 kHz Carrier wave pulse acquired using a source wavelet extracted from the data itself. Processing steps include automatically picking of the seafloor, burst noise removing, time-frequency noise attenuation, spherical divergence correction, butterworth and 2D spatial filtering. Finally, reflection strength (envelope of the signal) has been calculated and time-variant amplitude corrected for displaying and interpretation. Different sedimentary features such as bedforms, mass-movement deposits, erosive surfaces, fluid dynamic features and contourites have been defined. Most of tributaries show a progressive indentation and features observed in the upper courses are related to the erosive processes e.g. a dense network of dendritic gullies and minor scars and falls affecting the canyon walls. The seafloor of the southern margin is highly irregular defining an area that extends from 600 to 2240 mwd affected by a mass flows deposits composite. In contrast, the northern margin presents a set of nested concave-downward scars, with a W-E trend, and lengths of 2 to 8 km

Contourite deposits are generated by the interplay between deepwater bottom-currents, sediment supply and seafloor topography. The Gulf of Cadiz, in the Southwest Iberian margin, is a famous example of extensive contourite deposition driven by the Mediterranean Outflow Water (MOW), which exits the Strait of Gibraltar, flows northward following the coastline and distributes the sediments coming from the Guadalquivir and Guadiana rivers. The MOW and related contourite deposits affect the stability of the SW Iberian margin in several ways: on one hand it increases the sedimentation rate, favoring the development of excess pore pressure, while on the other hand, by depositing sand it allows pore water pressure to dissipate, potentially increasing the stability of the slope. In the Gulf of Cadiz, grain size distribution of contourite deposits is influenced by the seafloor morphology, which splits the MOW in different branches, and by the alternation of glacial and interglacial periods that affected the MOW hydrodynamic regimes. Fine clay packages alternates with clean sand formations according to the capacity of transport of the bottom-current in a specific area. Generally speaking, coarser deposits are found in the areas of higher MOW flow energy, such as in the shallower part of the slope or in the area closer to the Strait of Gibraltar, while at higher water depths the sedimentation shifts to progressively finer grain sizes as the MOW gets weaker. Previous works show that at present-day the MOW flows at a maximum depth of 1400 m, while during glacial periods the bottom-current could have reached higher depths. In this study we derived the different maximum depths at which the MOW flowed by analyzing the distribution of sands at different depths along the Alentejo basin slope, in the Northern sector of the Gulf of Cadiz. Here we show how changes in sand distribution along slope, within the stratigraphic units deposited between the Neogene and the present day, are drive

In the shallow region of subduction zones, topographic variations of the interplate interface condition the structural integrity of the upper plate, and thus the distribution of elastic properties in this region, which determines its tsunamigenic potential. Yet, we know little about the distribution of elastic properties in these shallow regions, which yields large uncertainty during tsunami hazard assessment. Here we assess topographic variations of the interplate boundary as well as the distribution of elastic properties of the upper plate in two tsunamigenic regions of the Middle American Trench. We focus on the rupture area of three tsunami earthquakes, the 1992 Nicaragua event, and the 1932 and 1995 Jalisco-Colima earthquakes (Pacific Mexican coast). We use 2D coincident wide-angle (WAS) and multichannel seismic (MCS) lines acquired across the rupture area of each event to jointly invert refracted and reflected travel-times (TT) and obtain the P-wave velocity (Vp) structure of the tsunamigenic region of the upper plate, and the geometry of the interplate boundary. Mixing both types of seismic data allowed for the first time to retrieve small-scale local topographic variations of the interplate that would have been omitted with the classical inversion of WAS TT. From Vp, we derive other elastic parameters namely, density, S-wave velocity, and rigidity using well-established empirical relationships. The results show that the heterogeneous distribution of the elastic properties of the upper plate in the shallow tsunamigenic region correlates with topographic variations of the interplate in both margins. These results not only sustain the direct relationship between the interplate relief and the tectonic structure of the overriding plate as it has been already stated by previous authors, but they also allow to quantify the relationship between topographic highs of the subducted plate with low rigidity regions in the upper plate. This quantification is of paramount

The Lineament South (LS) is a major WNW-ESE trending dextral strike-slip fault located along all the Gulf of Cadiz (SW Iberian margin), and it has been considered as the plate boundary between Africa and Eurasia. The SW Iberian margin hosts a moderate to intermediate seismic activity, however, largest and destructive earthquakes and tsunamis have occurred in this area, such as the 1st of November 1755 Lisbon earthquake and tsunami (Mw ≥ 8.5) and the 28th February 1969 earthquake (Mw 7.8). Our work focus on the LS active structure and their potential seismic and tsunami hazard. To study the LS, we integrated the most advanced technologies in marine geosciences covering different scales of resolution, such as: a) Multibeam echosounder that allows us to obtain a bathymetric map that provides information of the seafloor; b) Sub-bottom profiler to acquire high-resolution seismic profiles of the uppermost layers below seafloor; c) Autonomous Underwater Vehicle (AUV) “Abyss” to carry out a micro-bathymetric survey (2 m resolution); and d) High-resolution 2D multichannel seismic profiles. With these dataset, we characterized the LS structure and their sub-surface, calculated the maximum magnitude earthquake and modelled the worst-case tsunami scenario that this fault may produce. The workflow to develop the tsunami modelling involves the following tasks: 1) Interpretation of the high-resolution seismic profiles; 2) Map the trace of the LS fault; 3) Generate a seismo-stratigraphic model of the fault subsurface; 4) Define the specific attributes and seismic/tsunamigenic parameters of the LS fault system; 5) Determine the maximum magnitude and slip according to Leonard (2014) scaling-laws; and 6) Run the tsunami simulation using the Tsunami-HySEA software. The LS extends for more than 370 km, from the Horseshoe Abyssal Plain to the Gulf of Cadiz Imbricated Wedge, as demonstrated for the sequence of MCS profiles across the lineament. In the AUV map, we can recognize fault trace

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 seismic activity is mainly characterized by low to moderate magnitude events, large and destructive earthquakes (I > IX) have occurred in this region (i.e., 1522 Almeria, 1790 Oran, 1910 Adra, 1994 and 2004 Al-Hoceima or 2016 Al-Idrissi earthquakes). The identification and the seismogenic characterization of the active structures in the Alboran Sea using ultra high-resolution (UHR) geophysical data is essential to evaluate better the exposure of the South Iberian Peninsula and North African coasts to related natural hazards (i.e., large earthquakes and related tsunamis and triggered landslides). During the SHAKE cruise, the Asterx and Idefx AUVs (Ifremer, france) were used to acquire UHR bathymetric (1m grid) and seismic (cm vertical resolution) data across the main active faults systems in the Alboran Sea with the aim to carry out sub-aqueous paleoseismological studies. One of the studied active structures has been the Yusuf Fault System (YFS), a dextral strike-slip system that is one of the largest structures in the Alboran Sea and a lithospheric boundary between different crustal domains: the East Alboran Basin to the north and the North African Margin to the south. It trends WNW-ESE, is ~150 km-long and can be divided into two main segments (W and E), producing the formation of a pull-apart basin where both overlap. The analysis of the UHR geophysical dataset reveals that in the imaged area this system is a complex structure composed by an array of strike-slip faults. Most of them reach up and offset the seafloor and the upper Pleistocene to Holocene sedimentary units. The results of the on-fault paleoseismological analyses reveal that the YFS may have generated at least 8 earthquakes in recent times. Although a detailed on-site geochronology is not available, a regional chronostratigraphi

The megathrust topography is key in conditioning the structural integrity of the overriding plate, and thus, the generation of tsunamigenic structures. Our objective is to investigate the Rivera subduction zone, offshore the Mexican Pacific coast, known for hosting large megathrust tsunamigenic earthquakes (Mw > 7.5), and where little is known regarding the distribution of tsunamigenic structures along the margin. Our working hypothesis is that there is an interaction between the megathrust relief at the surface of the subducted slab (Rivera Plate) and the existence of tsunamigenic structures in the above unsubducted plate (North America). To investigate this interaction, we used seismic methods to characterize the variations of the physical properties of the overriding plate, generally related to tectonic (faults) structures that are sources of tsunamis, with the reliefs of the deeper subducted plate obtained with the same method. Here, we use spatially coincident 2D multichannel seismic (MCS, 5.85 km long-streamer) and active marine wide-angle seismic (WAS) data acquired during the TSUJAL survey in 2014 offshore west of Mexico to measure structural variations of the overriding plate and the megathrust interface. We have jointly inverted refracted and reflected travel-times (TT) from both MCS and WAS data to constrain the P-wave velocity (Vp) structure of the overriding plate and the geometry of the megathrust. Before the inversion and to increase the amount of refracted TT we have applied the downward continuation technique to MCS field data allowing to better image the refracted waves in the records. MCS data has a higher spatial sampling than OBS data, which translates into a higher density sampling of the refracted waves and hence the tomographic resolution. Therefore, the resulting tomographic model displays small-scale velocity structure variations of the overriding plate and the megathrust relief that would not be resolved with TT from OBS data only. We used

Marie Tharp (1920-2006) was a pioneer of modern oceanography. She was an American geologist and oceanographic cartographer who, together with his husband Bruce Heezen, generated the first bathymetric map of the Atlantic Ocean floor. Tharp's work revealed the detailed topography and geological landscape of the seafloor. Her work revealed the presence of a continuous rift valley along the Mid-Atlantic Ridge axis, causing a paradigm in earth sciences that led to the acceptance of plate tectonics and continental drift theories. Piecing maps together in the late 1940s and early 1950s, Marie and his partner Bruce Heezen discovered the 75.000 km underwater ridge bounding around the globe. By this finding, they laid the conclusion from geophysical data that the seafloor spreads from mid-ocean ridges and that continents are in motion with respect to one another¿a revolutionary geological theory at that time. Many years later, satellite images demonstrate that Tharp¿s maps were accurate. In this contribution, we focus on detailed bathymetric maps collected from year 1992 to today, which include bathymetric maps from diverse parts of the world. For instance, we will show a) Back-arc basins (i.e. the Bransfield Basin, Antarctica; and the North Fiji Basin, SW Pacific); b) Mid-ocean ridges and fracture zones (i.e. the MAR at the South of Azores, the MAR at the Oceanographer-Hayes, and the St. Paul Fracture Zone at the Equator), and c) Active tectonic structures from the Gulf of Cadiz and Alboran Sea, located at the Africa-Eurasia plate boundary (Gibraltar Arc). Regarding this last area, we will characterize the seafloor expression of the fault systems, as well as the subsurface structure of the faults in the Gulf of Cadiz and Alboran Sea. This zone is characterized by a moderate seismicity, mainly reverse and strike-slip focal mechanisms; although large historical (AD1755, AD1829) and instrumental earthquakes or large/great magnitude also occurred, such as the earthquakes of 1969

Large continental faults extend for thousands of kilometres and often form the tectonic boundaries between plates that are associated with prominent topographic features. In these active areas, well-defined faults produce large earthquakes, and thus imply a high seismic hazard. These paradigms are called into question in the Alboran Sea, which hosts an allegedly complex diffuse boundary between the Eurasia and Nubia plates, and we discovered one of the few examples worldwide of the initial stages of these key tectonic structures. On the 25th January 2016, a magnitude Mw6.4 submarine earthquake struck the north of the Moroccan coast, the largest event ever recorded in the Alboran Sea. The quake was preceded by an earthquake of magnitude Mw5.1 and was followed by numerous aftershocks whose locations mainly migrated to the south. The mainshock nucleated at a releasing bend of the poorly known Al-Idrissi Fault System (AIFS). According to slip inversion and aftershock distribution, we assume a rupture length of 18 km. Here we combine newly acquired multi-scale bathymetric and marine seismic reflection data with a resolution comparable to the studies on land, together with seismological data of the 2016 Mw 6.4 earthquake offshore Morocco – the largest event recorded in the area – to unveil the 3D geometry of the AIFS. We found that, despite its subdued relief, the AIFS is a crustal-scale boundary. We report evidence of left-lateral strike-slip displacement, characterize their fault segments and demonstrate that the AIFS is the source of the 2016 events. The occurrence of the Mw 6.4 earthquake and previous events of 1994 and 2004 supports that the AIFS is currently growing through propagation and linkage of its segments, which eventually might generate a greater rupture (up to Mw 7.6), increasing the potential hazard of the structure. The AIFS provides a unique model of the inception and growth of a young plate boundary system in the Alboran Sea (Western Mediterranean)

Según el World Wildlife Fund for Nature (Naciones Unidas, 2015) el 50% de la población mundial vive en la franja de costa marítima de 100 km, 16 de las 23 megaciudades del mundo están frente a los océanos, y 1000 millones de personas viven en comunidades con vínculos directos con el mar. Por tanto, el estudio de los procesos geológicos en el océano y sus geo-riesgos (entre ellos terremotos y tsunamis) son claves para la humanidad siendo las geociencias (geofísica y geología) marinas la disciplina apropiada. El estudio de los procesos geológicos en el océano (externos e internos) abarca a la geosfera, uno de los cuatro sistemas que interactúan en el planeta Tierra junto con la atmosfera, la hidrosfera y la biosfera. Se podría definir como el estudio de la secuencia de eventos naturales en el tiempo que ocurren en el océano y modifica las estructuras de la Tierra. Son el objeto de mi estudio desde la etapa universitaria mediante técnicas geofísicas, que son métodos indirectos fundamentalmente acústicos dada la imposibilidad de acceder al objeto de estudio bajo el océano. De todos los procesos geológicos, me centraré en los que modifican la litosfera (la capa sólida superficial de la Tierra), caracterizada por su rigidez. Su estructura es fragmentada, formando placas tectónicas y con tres tipos de límites claros: convergente (subducción), divergente (ruptura o rifting) y transformante. Los procesos geológicos son tradicionalmente separados en externos cuando la energía proviene del exterior (Sol) y modelan el relieve (erosión, transporte, sedimentación, deposición,…), e internos cuando la energía proviene del interior de la Tierra y modifican la estructura litosférica (convección, volcanismo, uplift, subducción, orogénesis,…) Esta charla de vocación científico-divulgativa está adaptada y basada en la que se presentó durante la segunda fase del concurso a científico titular de la plaza de título homónimo, en la que R. Bartolomé consiguió acceder a un puesto permanente e

A multi-scale dataset consisting of multi-beam echo-sounder, 2D multi-channel seismic and sidescan sonar (TOBI) data allows us to identify a large variety of morphologies originating from sedimentary and tectonic processes along the São Vicente Canyon (SVC), which is the largest submarine canyon developed in the external part of the Gulf of Cadiz. The SVC is located in one of the most seismogenic areas of Western Europe. The convergence between the Eurasian and African plates has controlled the formation and evolution of the canyon. The SVC is tectonically controlled by three main thrust faults: the Marquês de Pombal Fault, the São Vicente Fault and the Horseshoe Fault. No major rivers feed sediment to the canyon head, but the main sediment source is related to the dismantling of canyon flanks and the MOW (Mediterranean Overflow Water). This current contributes sediments by two different processes: a) conturites deposition at the head and flanks of the SVC that periodically fail into the canyon; and b) the coarser-grained and denser sediment of the MOW might be trapped at the head of the canyon and could develops into hyperpycnal flows. The SVC is characterized by retrogressive erosion being submarine landslide deposits and scars the main seafloor morphologies. The tectonic and stratigraphic interpretation of seismic profiles indicate that the SVC is a clear example of a diachronous and segmented canyon developed since the Late Miocene in an area of present-day active plate tectonics. This study investigates the interaction between active tectonics, the dynamics of submarine canyons and the resulting geomorphologies