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Depositional and erosional bedforms that shape prodelta deposits in the Gulf of Patti (southern Tyrrhenian Sea) and in the Al-Hoceima Bay (northern Morocco) were investigated using multibeam bathymetry as a basis for morphometric analysis. The two study areas have comparable structural settings and oceanographic regimes and share the occurrence of sediment undulations and closely spaced gullies. The resulting bedform fields are confined on prodelta deposits, from the inner to the outer shelf. The infrequent coexistence of these two types of bedforms on other Mediterranean margins makes our case study an ideal opportunity to investigate the processes that may control the combined or independent genesis of each type of bedform. Whereas gullies are more confidently interpreted as the result of erosion of the seafloor by hyperpycnal flows generated at river mouths and/or triggered by settling plumes and small-scale instabilities on delta front, unveiling the genetic mechanism behind sediment undulations is more difficult, and makes identifying the underlying processes, ranging from bottom currents to gravity flows or even internal waves, more ambiguous. Quantitative measurements of the main morphometric parameters of sediment undulations and gullies were computed to resolve relationships between their variability and their distribution over the prodelta area. Particular attention was paid to statistical analysis of sediment undulations using multivariate analysis based on principal component analysis (PCA) and k-mean fuzzy clustering. The individual and comparative analyses suggest that shelf gradients, location and distance from the river mouth, and sediment supply are keys in controlling the growth and scale of sediment undulations with respect to their distribution downslope. Although from our analysis, sedimentary gravity flows stand out as the most likely mechanism triggering the generation of sediment undulations, alternative causes (i.e., soft-sediment deformation or sediment remobilization by oceanographic processes) cannot be ruled out. Our results provide new insights into the possible origin of sediment undulations under the control of river-driven sediment gravity flows in prodelta settings, indicating that their concomitant occurrence with gullies is not accidental.

19 pages, 13 figures, 1 table, supplementary material https://doi.org/10.1016/j.margeo.2022.106739.-- Seismic reflection and bathymetric data collected during the MARLBORO and SARAS cruises are stored at SISMER repository (https://doi.org/10.17600/11480100, https://doi.org/10.17600/12450090, and https://campagnes.flotteoceanographique.fr/campagnes/12000010). Landslide parameters for MTDs mapped during this study are given in the appendix., Earthquakes are the most commonly cited cause of offshore slope failure, followed by high sedimentation rates and ensuing pore pressure build-up. In the South Alboran Sea, the moderate seismicity (Mw = 6.4) of the strike-slip Al Idrissi Fault Zone does not appear to control directly the landslides distribution. To provide a preliminary geohazard assessment, we characterized the spatial distribution, the volume and the ages of the submarine landslides from multibeam and seismic reflection data in the southern part of the Alboran Sea. Since the Quaternary numerous submarine landslide processes have affected the marine sedimentary cover with volumes of the mass transport deposits (MTD) estimated between 0.01 and 15 km3. West of the Al Idrissi Fault Zone, along the South Alboran Ridge's northern flank, the distribution of the MTD follows the SW-NE bank and ridge trend that correlates with blind thrusts and folds covered by a plastered contourite drift. A pockmark field, related to fluid escape, is visible near landslide scars where the contourite drift is relatively thicker. In this area, landslide scars occur on variable slopes (2–24°) and their associated MTDs show variable decompacted volumes (0.01-10 km3). East of the Al Idrissi Fault Zone, between the Alboran Ridge and the Pytheas Bank, the mapped MTDs have uneven volume. The smaller ones (10°), whereas those of the largest ones (3–15 km3) occur on gentler slopes (, This work was funded by the French programs Actions Marges, Défi Risques Naturels CNRS-IRD (MITI-ALARM) and UPMC-Emergence (ALARM project), the ALBAMAR JCJC ANR-17-03CE-0004, the EUROFLEETS program (FP7/2007-2013; n°228344), project FICTS-2011-03-01. Seismic reflection data were processed using the Seismic UNIX SU and Geovecteur© software. The processed seismic data were interpreted using Kingdom IHS Suite© software. This work also benefited from the DAMAGE (AEI/FEDER CGL2016-80687-R) and FAUCES (Ref CTM2015-65461-C2-R; MINCIU/FEDER) Projects financed by “Ministerio de Economía y Competitividad y al Fondo Europeo de Desarrollo Regional” (FEDER). This work acknowledges the ‘Severo Ochoa Centre of Excellence’ accreditation of ICM-CSIC (CEX2019-000928-S

This study was supported by projects CGL2016-80687-R AEI/FEDER, P18-RT-3275, B-RNM-301-UGR18 and RNM148 (Junta de Andalucia/FEDER); ALBAMAR JCJC ANR-17-CE030004; the EUROFLEETS program (FP7/2007-2013; no 228344); project FICTS-2011-03-01; and the FPU PhD grant (16/04038), and also by the Spanish Government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000928-S)., The IHS KINGDOM software package was utilized in the present study. We also to the marine surveys, MARLBORO2 and SARAS (https://campagnes.flotteoceanographique.fr/ campagnes/12450090/; https://campagnes.flotteoceanographique. fr/campagnes/12000010/)., Automation of the throw backstripping method has proven to be an effective tool for the determination of the evolution of tectonic activity in wide fault zones. This method has been applied to the Al Hoceima Bay (southwesternmost Mediterranean, Alboran Sea) for a time period covering the last 280 kyr on 672 faults imaged on 265 high-resolution seismic reflection profiles. This area was affected by major earthquakes and corresponds to a transtensional basin deformed by growth faults. The automated application of throw backstripping allowed for a faster deciphering of the migration of tectonic activity. Results show a westward migration of the deformation with quickly increasing deformation rates in the most recent time frames near Al Hoceima, one of the most populated cities. This migration is in agreement with the current seismicity, the GPS data, and recent brittle deformation data. Vertical throw rates of up to 0.47 mm/year have been calculated, for the most recent time periods, in segments of the Bokkoya fault zone. The westward migration of the deformation fits with the reconstruction suggested by the westernmost Mediterranean geodynamic models during the Pleistocene epoch, and it might be the consequence of the interaction between the northwest (NW) movement of the South Alboran indenter and the back Rif south-westward displacement. The highly accurate constraints of the evolution of the tectonic activity offered by this automation will substantially improve the seismic hazard assessment., Junta de Andalucia European Commission CGL2016-80687-R AEI/FEDER P18-RT-3275 B-RNM-301-UGR18 RNM148, ALBAMAR JCJC ANR-17-CE030004, EUROFLEETS program (FP7/2007-2013) 228344, German Research Foundation (DFG) 16/04038, Spanish Government through the 'Severo Ochoa Centre of Excellence' accreditation CEX2019-000928-S, FICTS-2011-03-01

25 pages, 14 figures, 1 table.-- Seismic reflection and bathymetric data collected during the MARLBORO and SARAS cruises are stored at SISMER and Seanoe (SEA scieNtific Open data Edition) (https://doi.org/10.17600/11480100, https://doi.org/10.17600/12450090, and https://campagnes.flotteoceanographique.fr/campagnes/12000010), Since the Miocene, the thinned continental crust below the Alboran Sea and its overlying sedimentary cover have been undergoing deformation caused by both convergence of Eurasia and Africa and by deep processes related to the Tethyan slab retreat. Part of this deformation is recorded at the Xauen and Tofiño banks in the southern Alboran Sea. Using swath bathymetry and multichannel seismic reflection data, we identified different stages and styles of deformation. The South Alboran Basin is made up of Early Miocene to Pliocene sedimentary layers that correlate with the West Alboran Basin depocenter and are dominated by E‐W trending folds and thrusts. The Xauen and Tofiño Banks first recorded the phase of extension and strike‐slip movement during the slab retreat, followed by the phase of compressional inversion since the Tortonian and are now structured by tight folds, thrusts, and mud bodies. This study proposes that the Banks were located on the southern‐inherited Subduction Tear Edge Propagator (STEP) fault related to the westward migration of the Alboran domain during the Miocene. The STEP fault zone, acting as a boundary between the African block and the Alboran block, was located along the onshore Jebha‐Nekor fault and the offshore Alboran Ridge and the Yusuf fault zone. Thick‐skinned and thin‐skinned shortening occurred when slab retreat stopped, and inversion began. The present‐day style of the deformation seems to be linked to a decollement level made of undercompacted shale on top of the Ghomaride complex, This work was funded by the French program Actions Marges, the ALBAMAR JCJC ANR‐17‐CE03‐0004, the EUROFLEETS program (FP7/2007‐2013; 228344), and project FICTS‐2011‐03‐01. [...] This work also benefited from the DAMAGE (AEI/FEDER CGL2016‐80687‐R) and Fauces (Ref CTM2015‐65461‐C2‐R; MINCIU/FEDER) Projects financed by “Ministerio de Economía y Competitividad y al Fondo Europeo de Desarrollo Regional” (FEDER)., With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

25 pages, 16 figures, supplement https://www.solid-earth.net/11/741/2020/se-11-741-2020-supplement.pdf.- Seismic profiles presented in this article are provided in the Supplement. The bathymetry of the seafloor provided in this article is not publicly available, Progress in the understanding and dating of the sedimentary record of the Alboran Basin allows us to propose a model of its tectonic evolution since the Pliocene. After a period of extension, the Alboran Basin underwent a progressive tectonic inversion starting around 9–7.5 Ma. The Alboran Ridge is a NE–SW transpressive structure accommodating the shortening in the basin. We mapped its southwestern termination, a Pliocene rhombic structure exhibiting series of folds and thrusts. The active Al-Idrissi Fault zone (AIF) is a Pleistocene strike-slip structure trending NNE–SSW. The AIF crosses the Alboran Ridge and connects to the transtensive Nekor Basin and the Nekor Fault to the south. In the Moroccan shelf and at the edge of a submerged volcano we dated the inception of the local subsidence at 1.81–1.12 Ma. The subsidence marks the propagation of the AIF toward the Nekor Basin. Pliocene thrusts and folds and Quaternary transtension appear at first sight to act at different tectonic periods but reflect the long-term evolution of a transpressive system. Despite the constant direction of Africa–Eurasia convergence since 6 Ma, along the southern margin of the Alboran Basin, the Pliocene–Quaternary compression evolves from transpressive to transtensive along the AIF and the Nekor Basin. This system reflects the logical evolution of the deformation of the Alboran Basin under the indentation of the African lithosphere, This research has been supported by the CNRS-INSU-TOTAL-BRGM-IFREMER Actions Marges program, EUROFLEETS program FP7/2007-2013 (grant no. 228344), EU Regional Structural Fund (grant no. FICTS-2011-03-01) and DAMAGE Project (project no. FEDER/CGL2016-80687-R AEI), Fauces Project (project no. FEDER/CTM2015-65461-C2-R; MINCI), ALBAMAR Project (project no. ANR/ANR-17-CE03-0004), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

This study provides a first characterization of the geomorphic features and relative habitats of the Francesc Pages Bank, located on the upper slope of the Moroccan continental margin in the southern Alboran Sea, western Mediterranean. The Francesc Pages Bank is an ellipsoidal structural high covering 80 km2 within a depth range of 76–580 m. High-resolution swath mapping allowed to recognize different geomorphic features on the top of the Bank, including crests, banks and ridges. An automatic classification of multibeam sonar data has been performed to identify and map the different physical habitats using terrain parameters derived from the bathymetry as surrogate descriptors. A remotely operated vehicle (ROV) video track acquired in the area showed the occurrence of several dense and uncommonly well-preserved megabenthic assemblages composed of gorgonians, soft corals, and several demosponge species. Multivariate statistical analyses performed on species abundance and terrain parameters derived from ROV observations allowed to define the main substrates governing the distribution of the observed benthic species, which coincide with some of the physical habitats detected by the multibeam automated classification.

20 pages, 14 figures, 1 table, In active basins, tectonics can segment the continental shelf and control its stratigraphic architecture and physiography. Segmentation can explain the local evolution and morphology of the continental shelf because of sea-level variations, local tectonic segmentation and hydrodynamic processes. Here we investigate the tectonically active Morocco continental margin (southern Alboran Sea) using high-resolution seismic profiles and multibeam bathymetric data. The active faults bounding the transtensive Nekor basin triggered the segmentation of the shelf into three sectors showing different subsidence rates: a western sector corresponding to an extensive fault relay, a central sector corresponding to the subsiding Al-Hoceima Bay and an eastern sector corresponding to the footwall of the Trougout senestral normal fault. Results show that the staircase morphology of the shelf corresponds to successive submarine terraces at the shelf edge (ST1), mid-shelf (ST2) and inner-shelf (ST3) around −110 m,-80 m, and −40 to −20 m deep, respectively. The terraces correspond to the top of prograding wedges seaward and are erosive landward. They are correlated with stillstand from the Last Glacial Maximum to the Holocene highstand. Above the terraces, sub-aqueous dune fields are interpreted as degraded and deposited during the post-glacial transgression. In the central sector, typical delta front seafloor undulations on the shelf and crescent shaped bedforms at the head of marine incisions on the upper slope denote a fluvial influence during the Holocene. Seismic stratigraphy analysis revealed the preservation of six seismic units bounded by polygenic regional unconformities (S1, S2, S3, S4 and S5). Based on comparison with other Mediterranean margins, S1 to S5 are attributed to 4th order maximum regressive surface. We discuss the local preservation of the system tracts as a function of the vertical motion and the physiography of this tectonically active domain. This study provides useful clues for future local paleo-seismic analysis and to advance our understanding of sedimentary processes in active areas, This work was funded by the French program Actions Marges, the EUROFLEETS program (FP7/2007-2013; n°228344), project FICTS-2011-03-01. Seismic reflection data were processed using the Seismic UNIX SU and Geovecteur software. [...]. This work also benefited from a State Grant from the French Agence Nationale de la Recherche (ANR) in the Program « Investissements d'avenir » reference ANR-10-LABX-19-01, Labex Mer and from the Fauces Project (Ref CTM2015-65461-C2-R; MINCIU/FEDER) financed by "Ministerio de Economía y Competitividad y al Fondo Europeo de Desarrollo Regional" (FEDER)

Rodriguez, Mathieu ... et al.-- 16 pages, 8 figures, 2 tables, The active Eurasia–Nubia plate boundary runs across the Alboran Sea in the Western Mediterranean Sea, where the connection between the Atlantic and Mediterranean water masses occurs. Earthquakes above magnitude Mw > 6 may favour the occurrence of landslides within contouritic drifts in the Alboran Sea. A compilation of recent multibeam data reveals for the first time the distribution of slope failures along the Xauen–Tofiño banks, in the southern Alboran Sea. Here, we provide a detailed mapping and description of the morphology of eight Holocene landslides, including volume estimations of the failed mass and the related mass transport deposits (MTDs). The most voluminous landslide mobilized ∼0.5 km3 of sediment at the initial stage of slope failure, and formed a ∼2.2–5.6 km3 MTD. A finite-difference numerical model, assimilating the landslide to a granular flow, simulates tsunami generation and propagation for a slide similar to the most voluminous one. Simulations show that the coastline of Al Hoceima may be impacted by a ∼0.5-m-high tsunami wave, whereas the coastline of Al Jebha may be impacted by a ∼1-m-high tsunami wave, only ∼13 min after sediment failure. The 0.2-m-high tsunami waves may impact the southern Spanish coast of the Iberian Peninsula ∼20 min after slide initiation. Although the elevations of the modeled tsunami waves are modest, landslides from the Xauen–Tofiño banks may represent a more dangerous source of tsunami in some parts of the Moroccan coast than earthquakes, This work was funded by the French program Actions Marges, the EUROFLEETS program (FP7/2007-2013; no. 228344), project FICTS-2011-03-01 and is a contribution to the CONTOURIBER (CTM2008-06399-MAR) and MONTERA (CTM-14157-C02) projects, funded by the Spanish Science and Innovation Ministry

The style of inversion of inherited extensional basins in the Western Alps is investigated through thermo-mechanical modelling. Two-dimensional models consist of a half-graben embedded in a relatively strong crust (basement) and filled with weak syn-rift sediments (cover). We investigate the relative influence of the internal friction (µ) of the basin-bounding normal fault, tectonic burial (h) under an overlying nappe and the geothermal gradient. We use a viscoplastic model with symmetrical shortening. The inherited normal fault is implemented as a curved thin body with a variable friction coefficient (µ) ranging from 0.1 to 0.6. The style of basin inversion is controlled at shallow depth by the internal friction coefficient, whose influence decreases with the increase of both burial depth and geothermal gradient. With increasing burial and/or geothermal gradient, fault reactivation is inhibited and distributed deformation in the basement induces the vertical extrusion of the cover. The basin inversion is accompanied by distributed deformation in the cover and by the shearing of the basin and basement interface. The results are consistent with the style of inversion of inherited half-grabens in the external Western Alps, where no significant fault reactivation occurred owing to tectonic burial underneath the Alpine internal units during the early Alpine collision.

International audience; The geodynamic processes in the western Mediterranean are driven by both deep (mantle) processes such as slab-rollback or delamination, oblique plate convergence and inherited structures. The present-day deformation of the Alboran Sea and in particular the Nekor basin area is linked to these coeval effects. The seismically active Nekor basin is an extensional basin formed in a convergent setting at the eastern part of the Rif Chain whose boundaries extend both onshore and offshore Morocco. We propose a new structural model of the Nekor basin based on high-resolution offshore data compiled from recent seismic reflection profiles, swath bathymetry acquisitions and industrial seismic reflection profiles. The new data set shows that the northern limit of the basin is oriented N49° with right-stepping faults from the Bousekkour–Aghbal fault to the sinistral Bokkoya fault zone. This pattern indicates the presence of an inherited left-lateral basement fault parallel to the major inherited Nekor fault. This fault has been interpreted as a Quaternary active left-lateral transfer fault localized on weak structural discontinuities inherited from the orogenic period. Onshore and offshore active faults enclose a rhombohedral tectonic Nekor Basin. Normal faults oriented N155° offset the most recent Quaternary deposits in the Nekor basin, and indicate the transtensional behaviour of this basin. The geometry of these faults suggests a likely rollover structure and the presence at depth of a crustal detachment. Inactive Plio-Quaternary normal faults to the east of the Ras Tarf promontory and geometries of depocentres seem to indicate the migration of deformation from east to west. The local orientations of horizontal stress directions deduced from normal fault orientations are compatible with the extrusion of the Rifian units and coherent with the westward rollback of the Tethyan slab and the localization of the present-day slab detachment or delamination.

We explored the submarine portions of the Enriquillo–Plantain Garden Fault zone (EPGFZ) and the Septentrional–Oriente Fault zone (SOFZ) along the Northern Caribbean plate boundary using high-resolution multibeam echo-sounding and shallow seismic reflection. The bathymetric data shed light on poorly documented or previously unknown submarine fault zones running over 200 km between Haiti and Jamaica (EPGFZ) and 300 km between the Dominican Republic and Cuba (SOFZ). The primary plate-boundary structures are a series of strike-slip fault segments associated with pressure ridges, restraining bends, step overs and dogleg offsets indicating very active tectonics. Several distinct segments 50–100 km long cut across pre-existing structures inherited from former tectonic regimes or bypass recent morphologies formed under the current strike-slip regime. Along the most recent trace of the SOFZ, we measured a strike-slip offset of 16.5 km, which indicates steady activity for the past ~1.8 Ma if its current GPS-derived motion of 9.8 ± 2 mm a−1 has remained stable during the entire Quaternary.

D'Acremont, E. ... et. al.-- 7 pages, 4 figures, Two recent destructive earthquakes in 1994 and 2004 near Al Hoceima highlight that the northern Moroccan margin is one of the most seismically active regions of the Western Mediterranean area. Despite onshore geodetic, seismological and tectonic field studies, the onshore–offshore location and extent of the main active faults remain poorly constrained. Offshore Al Hoceima, high-resolution seismic reflection and swath-bathymetry have been recently acquired during the Marlboro-2 cruise. These data at shallow water depth, close to the coast, allow us to describe the location, continuity and geometry of three active faults bounding the offshore Nekor basin. The well-expressed normal left-lateral onshore Trougout fault can be followed offshore during several kilometers with a N171°E ± 3° trend. Westward, the Bousekkour–Aghbal normal left-lateral onshore fault is expressed offshore with a N020°E±4° trending fault. The N030°E±2° Bokkoya fault corresponds to the western boundary of the Plio-Quaternary offshore Nekor basin in the Al Hoceima bay and seems to define an en échelon tectonic pattern with the Bousekkour–Aghbal fault. We propose that these three faults are part of the complex transtensional system between the Nekor fault and the Al-Idrissi fault zone. Our characterization of the offshore expression of active faulting in the Al Hoceima region is consistent with the geometry and nature of the active fault planes deduced from onshore geomorphological and morphotectonic analyses, as well as seismological, geodetic and geodynamic data. © 2014 Elsevier B.V., This work was funded by the French programs: LabexMER “Investment for the future” (ANR-10 LABX-19-01) and the Actions Marges (Total, CNRS-INSU, Ifremer, BRGM). The CNRS-INSU provided marine facilities