Special issue: Deep Seismix.-- 15 pages, 8 figures, The Palomares continental margin is located in the southeastern part of Spain. The margin main structure was formed during Miocene times, and it is currently part of the wide deformation zone characterizing the region between the Iberian and African plates, where no well-defined plate boundary occurs. The convergence between these two plates is here accommodated by several structures, including the left lateral strike–slip Palomares Fault. The region is characterized by sparse, low to moderate magnitude (Mw < 5.2) shallow instrumental earthquakes, although large historical events have also occurred. To understand the recent tectonic history of the margin we analyze new high-resolution multibeam bathymetry data and re-processed three multichannel seismic reflection profiles crossing the main structures. The analysis of seafloor morphology and associated subsurface structure provides new insights of the active tectonic features of the area. In contrast to other segments of the southeastern Iberian margin, the Palomares margin contains numerous large and comparatively closely spaced canyons with heads that reach near the coast. The margin relief is also characterized by the presence of three prominent igneous submarine ridges that include the Aguilas, Abubacer and Maimonides highs. Erosive processes evidenced by a number of scars, slope failures, gullies and canyon incisions shape the present-day relief of the Palomares margin. Seismic images reveal the deep structure distinguishing between Miocene structures related to the formation of the margin and currently active features, some of which may reactivate inherited structures. The structure of the margin started with an extensional phase accompanied by volcanic accretion during the Serravallian, followed by a compressional pulse that started during the Latemost Tortonian. Nowadays, tectonic activity offshore is subdued and limited to few, minor faults, in comparison with the activity recorded onshore. The deep Algero-Balearic Basin is affected by surficial processes, associated to halokinesis of Messinian evaporites, The authors acknowledge the support from the Spanish Ministry of Economy and Competitiveness through the Complementary Action ESF TopoEurope TOPOMED (CGL2008-03474-E/BTE), National Projects SHAKE (CGL2011-30005-C02-02) and INSIGHT (CTM2015-70155-R), and the EU-COST Action FLOWS (ES 1301). Also extend our thanks to the Spanish Oceanographic Institute and Secretariat General of the Sea who provided the technical, financial and ship-time for the acquisition of the bathymetric data. This work was supported by the Spanish Ministry of Education, Culture and Sport through the FPU fellowship 2013–2017 to L. Gómez de la Peña (AP2012-1579), Peer Reviewed

19 pages, 10 figures, 2 tables, supporting information https://doi.org/10.1111/bre.12225, High‐resolution acoustic and seismic data acquired 100 km offshore Cape São Vicente, image with unprecedented detail one of the largest active reverse faults of the SW Iberian Margin, the Horseshoe Fault (HF). The HF region is an area seismogenically active, source of the largest magnitude instrumental and historical earthquake (Mw > 6) occurred in the SW Iberian Margin. The HF corresponds to a N40 trending, 110 km long, and NW‐verging active thrust that affects the whole sedimentary sequence and reaches up to the seafloor, generating a relief of more than 1 km. The along‐strike structural variability as well as fault trend suggests that the HF is composed by three main sub‐segments: North (N25), Central (N50) and South (N45). Swath‐bathymetry, TOBI sidescan sonar backscatter and parametric echosounder TOPAS profiles reveal the surface morphology of the HF block, characterized by several, steep (20°) small scarps located on the hangingwall, and a succession of mass transport deposits (i.e. turbidites) on its footwall, located in the Horseshoe Abyssal Plain. A succession of pre‐stack depth‐migrated multichannel seismic reflection profiles across the HF and neighbouring areas allowed us to constrain their seismo‐stratigraphy, structural geometry, tectono‐sedimentary evolution from Upper Jurassic to present‐day, and to calculate their fault parameters. Finally, on the basis of segment length, surface fault area and seismogenic depth we evaluated the seismic potential of the HF, which in the worst‐case scenario may generate an earthquake of magnitude Mw 7.8 ± 0.1. Thus, considering the tectonic behaviour and near‐shore location, the HF should be recognized in seismic and tsunami hazard assessment models of Western Europe and North Africa, The authors acknowledge the support of the Spanish Ministry of Science and Innovation (MICINN) through Acción Especial HITS (REN2000‐2150‐E) and National Projects EVENT (CGL2006‐12861‐C02‐02), SHAKE (CGL2011‐30005‐C02‐02), and INSIGHT (CTM2015‐70155‐R); the European Access of Seafloor Survey Systems EASSS‐III programme of the EC (HPRI‐CT99‐0047), the European Transnational Access SALVADORE program of the EU (RITA‐CT‐2004‐505322), the ESF EuroMargins SWIM project (01‐LEG‐EMA09F and REN2002‐11234E‐MAR), the EU program “Global Change and Ecosystems” contract n. 037110 (NEAREST), and the RSS “James Cook” Cruise JC027 of the National Oceanography Centre (Southampton, UK). We also acknowledge funding from the MICINN through the “Ramon y Cajal” program (R. Bartolome). [...] This work was carried out within the Grups de Recerca de la Generalitat de Catalunya B‐CSI (2014 SGR 940), Peer Reviewed

19 pages, 13 figures, 3 tables, 2 appendices, Mud Volcanism and fluid seepage are widespread phenomena in the Gulf of Cadiz (SW Iberian Margin). In this seismically active region located at the boundary between the African and Eurasian plates, fluid flow is typically focused on deeply rooted active strike-slip faults. The geochemical signature of emanating fluids from various mud volcanoes (MVs) has been interpreted as being largely affected by clay mineral dehydration and recrystallization of Upper Jurassic carbonates. Here we present the results of a novel, fully-coupled 1D basin-scale reactive-transport model capable of simulating major fluid forming processes and related geochemical signatures by considering the growth of the sediment column over time, compaction of sediments, diffusion and advection of fluids, as well as convective and conductive heat flow. The outcome of the model is a realistic approximation to the development of the sediment pore water system over geological time scales in the Gulf of Cadiz. Combined with a geochemical reaction transport model for clay mineral dehydration and calcium carbonate recrystallization, we were able to reproduce measured concentrations of Cl, strontium and 87Sr/86Sr of emanating mud volcano fluids. These results support previously made qualitative interpretations and add further constraints on fluid forming processes, reaction rates and source depths. The geochemical signature at Porto MV posed a specific problem, because of insufficient constraints on non-radiogenic 87Sr/86Sr sources at this location. We favour a scenario of basement-derived fluid injection into basal Upper Jurassic carbonate deposits (Hensen et al., 2015). Although the mechanism behind such basement-derived flow, e.g. along permeable faults, remains speculative at this stage, it provides an additional source of low 87Sr/86Sr fluids and offers an idea on how formation water from the deepest sedimentary strata above the basement can be mobilized and eventually initiate the advection of fluids feeding MVs at the seafloor.

The dynamic reactive-transport model presented in this study provides a new tool addressing the combined simulation of complex physical-geochemical processes in sedimentary systems. The model can easily be extended and applied to similar geological settings, and thus help us to provide a fundamental understanding of fluid dynamics and element recycling in sedimentary basins, The manuscript benefited from additional support by the project FLOWS (EU-COST Action 1301). Project CTM2015-70155-R (INSIGHT) has been funded through the Spanish Ministry of Science and Innovation, Peer Reviewed

26 pages, 15 figures, tables, supporting information https://doi.org/10.1029/2017TC004946.-- All the data used are listed in the references or archived at the Barcelona‐CSI repository at the ICM (TOPOMED, EVENT‐DEEP, and ESCI cruises, http://www.icm.csic.es) and at the UTIG repository (CONRAD cruise, http://www.udc.ig.utexas.edu/sdc/).-- This work has been carried out within Grup de Recerca Consolidat de la Generalitat de Catalunya “Barcelona Center for Subsurface Imaging” (2017 SGR 1662), The Alboran Basin in the westernmost Mediterranean hosts the orogenic boundary between the Iberian and African plates. Although numerous geophysical studies of crustal structure onshore Iberia have been carried out during the last decade, the crustal structure of the Alboran Basin has comparatively been poorly studied. We analyze crustal-scale images of a grid of new and reprocessed multichannel seismic profiles showing the tectonic structure and variations in the reflective character of the crust of the basin. The nature of the distinct domains has been ground-truthed using available basement samples from drilling and dredging. Our results reveal four different crustal types—domains—of the Alboran Basin: (a) a thin continental crust underneath the West Alboran and Malaga basins, which transitions to (b) a magmatic arc crust in the central part of the Alboran Sea and the East Alboran Basin; (c) the North African continental crust containing the Pytheas and Habibas subbasins; and (d) the oceanic crust in the transition toward the Algero-Balearic Basin. The Alboran Basin crust is configured in a fore-arc basin (West Alboran and Malaga basins), a magmatic arc (central and East Alboran), and a back-arc system in the easternmost part of the East Alboran Basin and mainly Algero-Balearic Basin. The North African continental crust is influenced by arc-related magmatism along its edge and was probably affected by strike-slip tectonics during westward migration of the Miocene subduction system. The distribution of active tectonic structures in the current compressional setting generally corresponds to boundaries between domains, possibly representing inherited lithospheric-scale weak structures, The authors acknowledge support from the Spanish Ministry of Economy and Competitiveness through the Complementary Action ESF TopoEurope TOPOMED (CGL2008‐03474‐E/BTE), national projects EVENT (CGL2006‐12861‐C02‐02), INSIGHT (CTM2015‐70155‐R), FRAME (CTM‐2015‐71766‐R), and COST Action 1301 “FLOWS.” This work was supported by the Spanish Ministry of Education, Culture and Sport through the FPU fellowship 2013–2017 to L. Gómez de la Peña (AP2012‐1579). This publication is funded by the Cluster of Excellence “The Future Ocean,” within the framework of the Excellence Initiative by the Deutsche Forschungsgemeinschaft (DFG) on behalf of the German federal and state governments, Peer Reviewed

This article have a datasets associated "Regional centroid moment tensors for earthquakes in the 2016 South Alboran seismic crisis" http://hdl.handle.net/10261/177887, Large continental faults extend for thousands of kilometres to form boundaries between rigid tectonic blocks. These faults are associated with prominent topographic features and can produce large earthquakes. Here we show the first evidence of a major tectonic structure in its initial-stage, the Al-Idrissi Fault System (AIFS), in the Alboran Sea. Combining bathymetric and seismic reflection data, together with seismological analyses of the 2016 M-w 6.4 earthquake offshore Morocco - the largest event ever recorded in the area - we unveil a 3D geometry for the AIFS. We report evidence of left-lateral strike-slip displacement, characterise the fault segmentation and demonstrate that AIFS is the source of the 2016 events. The occurrence of the M-w 6.4 earthquake together with historical and instrumental events supports that the AIFS is currently growing through propagation and linkage of its segments. Thus, the AIFS provides a unique model of the inception and growth of a young plate boundary fault system., This research was supported by projects CGL2011-30005-C02-02, CTM2015-70155-R and Acción IDRISSI (MINECO/FEDER), shiptime on board the R/V Sarmiento de Gamboa and R/V Angeles Alvariño, EuroFleets-2 grant agreement 312762, and access to IFREMER AUVs AsterX and IdefX (France) through Ocean Facilities Exchange Group (OFEG). We also thank the Instituto Geografico Nacional (IGN, Spain) for providing seismological data. H.P. acknowledges the EU Horizon 2020 programme under grant
agreement No H2020-MSCA-IF-2014 657769. E.d’A. acknowledges the French programme Actions Marges, the LabexMER (ANR-10-LABX-19-01) and the EuroFleets grant agreement 228344., Peer reviewed

13 pages, 12 figures, 5 tables, Sample disturbance is still a key issue in offshore investigations, especially when logistic and financial limitations do not allow the use of drilling equipment. This paper focuses on the comparison between the disturbance induced by a conventional free-fall piston corer (FF) and a modified piston corer (AD) equipped with a velocity control (Angel Descent method). Twin core samples were retrieved in two successions of pelitic sediments with a prevailing non-clayey fraction and a non-negligible sandy fraction. Comparison was based on different acquisition, physical and mechanical parameters ranging from accelerometer data to magnetic susceptibility logs and geotechnical parameters from laboratory investigations, including oedometer compression tests and cyclic simple shear tests. Accelerometer data highlighted the sharp reduction in velocity obtained for AD samples. Magnetic susceptibility logs, characterized by a pattern of peaks induced by several volcaniclastic levels present in the succession, indicated that the AD method significantly reduces core shortening. Among geotechnical investigations, cyclic shear tests provided small-strain shear moduli always higher in AD samples, whilst the response of oedometer compression tests was equivocal. In fact, methods for assessing sample disturbance have demonstrated to bear limited effectiveness when applied to soils with relatively low clay content and significant overconsolidation as it is the case of the studied sediments, R. Urgeles and J. Llopart acknowledge funding from project INSIGHT (CTM2015-70155-R) jointly funded by the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund. The research was funded by grants awarded to FB, AC and PT from the National Research Program Flagship Projects RITMARE – The Italian Research for the Sea - coordinated by the Italian National Research Council, Peer Reviewed

16 pages, 11 figures, 1 table, supplementary data https://doi.org/10.1016/j.margeo.2020.106219, 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, The authors are grateful for funding from MINECO through projects HITS (AC 2011), IMPULS (REN 2003-05996/MAR), ESF-EUROCORES “EuroMargins” (REN2002-11234-E MAR), SWIM (AE MCYT-DGI 2006), INSIGHT (CTM2015-70155-R), a MINECO FPI-2016 grant (ref. BES-2016-078877) to Cristina S. Serra (ICM-CSIC), and a MICINN “Juan de la Cierva-2017” grant (ref. 33838) to Sara Martínez-Loriente (ICM-CSIC)., With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

21 pages, 16 figures, 2 tables, Submarine landslides are common geomorphological features of continental margins. Some of the largest submarine landslides occurred on low-angle (< 4°), sediment-starved margins, yet their preconditioning and trigger mechanisms are still largely unconstrained. The southwestern continental margin of the East Sea (between 37.5°N and 38.0°N), Korea, occupies a narrow shelf (< 10 km), is characterized by low sedimentation rates (~3–7 cm /ka) with an average gradient of less than 2°. Here, we investigate submarine landslides using newly collected datasets including multibeam echosounder (MBES), chirp sub-bottom profiler, multichannel seismic (MCS) data and ten piston cores. MBES data from the margin reveal at least four major submarine landslides initiated at depths of 400 m to over 600 m. These landslides left clear headwall scarps on the seafloor with reliefs reaching over ~130 m and extend for over 40 km. MCS data show that some of the failures have resulted in the complete disintegration of the failed mass, while others have resulted in the deposition of well-defined hummocky debris flows. Sediments recovered downslope of the headwall scarps contain slides and debris flow deposits and turbidites that are overlain by bioturbated hemipelagic layers. Radiocarbon dating from hemipelagic units overlying MTDs within the headwall scarps reveal that major failures occurred at ca. 11 to 19 ka, coinciding with the time of the Last Glacial Maximum (LGM) to early deglaciation. Since then, hemipelagic sedimentation has prevailed throughout the sediment starved slope. Slope stability analyses based on geotechnical properties of sediments indicate that all areas are stable under static, and even stable under loads derived from earthquakes in instrumental records, but there were probably earthquakes in pre-historical records (i.e., with a longer recurrence interval) of potentially significant larger magnitude. We suggest that the preferential occurrence of major failures adjacent to the major faults on the lower slope may ultimately be tectonic-controlled although other factors may have contributed as well. Our work shows that coarse-grained clastic sediments are abundant in the shallow subsurface and that these higher-permeability units, often identified as weak layers, would focus fluid flow and could act as slip planes for slope failure. Our data also indicate that tectonic steepening and gas charging are other key parameters for controlling instability in sediment-starved margins, This study was supported by the project entitled “Geological survey in the Korean Peninsula and publication of the geological maps (GP2020-009)” of the Korea Institute of Geoscience and Mineral Resources (KIGAM) funded by the Ministry of Science and ICT. The Spanish “Ministerio de Ciencia e Innovación” and the European Regional Development Fund through grant CTM2015-70155-R (project INSIGHT) are also acknowledged, With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI), Peer reviewed

16 pages, 16 figures, 6 tables, The SW Iberian continental margin is well recognized as a tectonically active area, where major canyons and mass wasting events are both present. Earthquake triggered submarine landslides may cause tsunami and result in catastrophic damage to bordering coastal areas. In this setting, submarine landslide susceptibility mapping represents a major step towards a regional risk mitigation strategy. Landslide susceptibility mapping in large offshore areas presents significant challenges as a result of the limited information on controlling variables, large uncertainties in triggering mechanisms and limited geotechnical data. In this study, a geotechnical model-based approach has been followed that narrows the range of controlling factors and, within a probabilistic framework, allows a systematic treatment of parameter uncertainties. This model-based analysis covers the whole SW Iberian margin increasing by three orders of magnitude the areal extent of precedent offshore slope stability susceptibility studies. This jump in spatial scale is facilitated by application of a systematic Bayesian updating procedure, to combine geotechnical information from global databases and that available from regional sites. Seismic shaking is estimated using an available regional database of seismogenic faults. These tools are implemented within a GIS to generate, via Montecarlo simulations, probabilistic landslide susceptibility maps based on two different analytical seismic infinite slope stability models. These models differ mainly in the form of their final results, either as distributions of slope stability safety factors or as distributions of seismic-triggered slope displacements. Receiving Operator Curves are used to assess the different landslide susceptibility predictions obtained against a comprehensive regional database of submarine landslides. It turns out that the models analyzed correctly predict 92% and 82% of the mapped landslide subset chosen for validation for pseudo-static and displacement-based method respectively. This suggests that, within the limits of the currently available databases, seismic events are the dominant factor at the origin of the submarine landslides mapped in the study area. An advantage of the framework presented is that it can quickly incorporate new regional geotechnical information or better regional landslide databases, as they become available, This research received funding from the European Union's Horizon 2020 research and innovating programme under the Marie Sklodowska-Curie grant agreement No 721403. The Spanish “Ministerio de Ciencia e Innovación” and the European Regional Development Fund through grant CTM2015-70155-R (project INSIGHT) are also acknowledged, With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI), Peer reviewed

19 pages, 14 figures, 1 table.-- Data Availability Statement: The original seismic images used for this publication are available online (at https://doi.org/10.5281/zenodo.4134048, Northern Tunisia contains the poorly defined boundary between the Nubia and Eurasian plates. Offshore north Tunisia, the continental margin is interpreted to be part of the North Africa collisional fold and thrust belt system, linking the Maghrebian and the Sicilian‐Apennine chains. The Tunisia margin deforms by a slow NW‐SE trending convergence resulting in a diffuse deformation zone with scarce and scattered seismicity, in contrast to the neighboring regions of north Algeria and north Sicily. The complex recent evolution of this region is poorly known due to the paucity of studies, particularly offshore in the north Tunisian continental margin. Here, we present the seismostratigraphic analysis of the last ~1.8 Ma tectonosedimentary evolution of this area. The seismostratigraphic analysis supports that individual Quaternary depocenters developed syntectonic to faulting and that faulting influenced sedimentation patterns. We identify an abrupt variation in the sediment accumulation rates (SARs) coeval to a change in the strata geometry of the units located near faults at 402 ± 5 ka (mid‐Middle Pleistocene), supporting a change in the rate of faulting associated to contraction tectonics. This change indicates that deformation is controlled by the NW‐SE convergence between Nubia and Eurasia, probably accelerated at the end of extension in the Tyrrhenian back‐arc. Therefore, the current driving mechanism in the Central Mediterranean is possibly lithospheric collision between Nubia and Eurasia, The authors were supported by the project Geomargen‐2 funded by REPSOL and the EU project EMODnet‐HRSM. Additional funding came from the Spanish Ministry of Science and Innovation projects: CTM2011‐30400‐C02‐01 “HADES,” CGL2011‐30005‐C02‐02 “SHAKE,” CTM2015‐70155‐R “INSIGHT,” and by Grup de Recerca de la Generalitat de Catalunya Barcelona Center for Subsurface Imaging (B‐CSI), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI), Peer reviewed

25 pages, 10 figures, 1 appendix, supporting information, https://doi.org/10.1029/2020JB021474.-- Data Availability Statement: Preprocessed prestack seismic data, processing horizons, migration velocities, and code to reproduce the results using Madagascar (Fomel et al., 2013) are archived in Ford (2020), Mass‐transport complexes (MTCs) are often characterized by small‐scale discontinuous internal structure, such as slide blocks, rough interfaces, faults, and truncated strata. Seismic images may not properly resolve such structure because seismic reflections are fundamentally limited in lateral resolution by the source bandwidth. The relatively weak seismic diffractions, instead, encode information on subwavelength‐scale structure, with superior illumination. In this paper, we compare diffraction imaging to conventional, full‐wavefield seismic imaging to characterize MTCs. We apply a seismic diffraction imaging workflow based on plane‐wave destruction filters to two 2D marine multichannel seismic profiles from the Gulf of Cadiz. We observe that MTCs generate a large amount of diffracted energy relative to the unfailed confining sediments. The diffraction images show that some of this energy is localized along existing discontinuities imaged by the full‐wavefield images. We demonstrate that, in combination with full‐wavefield images, diffraction images can be utilized to better discriminate the lateral extent of MTCs, particularly for thin bodies. We suggest that diffraction images may be a more physically correct alternative to commonly used seismic discontinuity attributes derived from full‐wavefield images. Finally, we outline an approach to utilize the out‐of‐plane diffractions generated by the 3D structure of MTCs, normally considered a nuisance in 2D seismic processing. We use a controlled synthetic test and a real‐data example to show that under certain conditions these out‐of‐plane diffractions might be used to constrain the minimum width of MTCs from single 2D seismic profiles, Data for this study were collected in the framework of the project INSIGHT (CTM2015‐70155‐R) funded by the Spanish “Ministerio de Ciencia e Innovación” and the European Regional Development Fund. J. Ford was supported by a Marie Curie Doctoral Fellowship through the SLATE Innovative Training Network within the European Union Framework Program for Research and Innovation Horizon 2020 under grant agreement no. 721403. With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI), Peer reviewed

9 pages, 6 figures, supplementary information https://doi.org/10.1038/s43247-021-00216-5.-- Data availability: The bathymetric data used for tsunami simulations are available from GEBCO (https://www.gebco.net/data_and_products/gridded_bathymetry_data/). Detailed bathymetry used to generate Figs. 1 and 2 is published in Zitellini et al 28. The epicentral location of the seismicity shown in Fig. 1 is from the IGN Seismic Catalogue (https://www.ign.es/web/ign/portal/sis-catalogo-terremotos). The HAT fault plane needed to reproduce the tsunami simulation is available in the figshare repository: https://doi.org/10.6084/m9.figshare.14589315.-- Code availability: The code necessary to reproduce the Fig. 3 is available in the figshare repository: https://doi.org/10.6084/m9.figshare.14589315, The southwest Iberia margin is widely believed to have hosted the 1755 Great Lisbon earthquake and ensuing tsunami, one of the most destructive natural events in European history. Here we combine geophysical data and numerical tsunami modelling to investigate the source and mechanism responsible for this event. We find 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. We present tsunami simulations with this fault as the source, and find that they reproduce reported tsunami energy propagation patterns, arrival-times and run up heights more successfully than other modelled sources. We propose that a reverse dip-slip mechanism on the northwest verging Horseshoe Abyssal plain Thrust, combined with the two-state mechanical behaviour of serpentinite, is the most likely candidate for the source of the 1755 Great Lisbon earthquake and for other recent large regional earthquakes, This work has been done in the framework of projects FRAME (CTM2015-71766-R) and INSIGHT (CTM2015-70155-R), both funded by the Spanish Plan of Research and Innovation, and has also had funding support of the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI). First author’s work was done in the framework of the “Juan de la Cierva - Incorporación” fellowship IJCI-2017-33838, Peer reviewed

28 pages, 10 figures, 1 table, supporting information https://doi.org/10.1111/sed.12844.-- Data availability The data that support the findings of this study are available from the corresponding author upon reasonable request., Synchronous interaction between bottom currents and turbidity currents has been reported often in channel–levée systems where the thickness of the turbidity currents exceeds that of the levées. Such interplay between along-slope and down-slope sedimentary processes is one of the mechanisms by which ‘mixed turbidite–contourite systems’ can originate. However, bottom currents flow over large areas of the seafloor, including continental slopes characterized by deeply incised submarine canyons rather than channel levées. In these cases, a direct interaction between along-slope and down-slope currents is, theoretically, unlikely to take place. In this study, oceanographic, swath bathymetry, multichannel seismic data and sediment cores are used to investigate a 25 km long, 10 km wide and up to 0.5 km thick deep-sea late Quaternary deposit that sits adjacent to the north-west flank of one of the major canyons in the North Atlantic, the São Vicente Canyon, in the Alentejo Basin (south-west Iberian margin). The area receives the influence of a strong bottom current, the Mediterranean Outflow Water, which has swept the continental slope at different water depth ranges during glacial and interglacial periods. Architectural patterns and sediment characteristics suggest that this sedimentary body, named Marquês de Pombal Drift, is the result of the interaction between the Mediterranean Outflow Water (particularly during cold periods) and turbidity currents flowing along the São Vicente Canyon. Because the canyon is incised significantly deeper (ca 1.5 km) than the thickness of turbidity currents, an additional process, in comparison to earlier models, is needed to allow the interaction with the Mediterranean Outflow Water and transport sediment out of the canyon. In the São Vicente Canyon, and likely in other canyons worldwide, interaction of turbidity currents with contour currents requires intermediate nepheloid layers that export the finer-grained fraction of turbidity currents out of the canyon at the boundary between major water masses, This research received funding by the European Union’s Horizon 2020 research and innovating programme under the Marie Sklodowska-Curie grant via project ITN-SLATE (grant agreement No 721403). The Spanish “Ministerio de Ciencia e Innovación” and the European Regional Development Fund are also acknowledged for funding through grant CTM2015-70155-R (project INSIGHT), With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed

19 pages, 9 figures, 1 table, supporting information https://doi. org/10.1029/2021JB022127.-- Data Availability Statement: Fault meshes and Slip distributions are available at the figshare repository: https://figshare.com/s/02e19886d2ded8ec9145. MCS data is available at the following published articles: SWIM profiles: Bartolome et al., (2012); Martínez-Loriente (2013); Martínez-Loriente et al., (2013); Martínez-Loriente et al., (2018). VOLTAIRE profiles: Banda et al., (1995); Zitellini et al., (2001); Terrinha et al., (2009). BIGSETS profiles: Zitellini et al., (2001); Zitellini et al., (2004); Vizcaino (2009); Serra et al., (2020). IAM profiles: Sartori et al., (1994); Jiménez-Munt et al., (2010); Terrinha et al., (2009); Zitellini et al., (2009). ARRIFANO profiles: Sartori et al., (1994); Zitellini et al., (2004); Serra et al., (2020). Bathymetry used for the tsunami simulations (Figures 3-7) is available in the SRTM public repository: https://www2.jpl.nasa.gov/srtm/. Detailed bathymetry used to define the fault traces is published in Zitellini et al., 2009. Seismicity data used in Figure 1a is available at the IGN catalog website: https://www.ign.es/web/ign/portal/sis-catalogo-terremotos, The SW Iberian margin is one of the most seismogenic and tsunamigenic areas in W-Europe, where large historical and instrumental destructive events occurred. To evaluate the sensitivity of the tsunami impact on the coast of SW Iberia and NW Morocco to the fault geometry and slip distribution for local earthquakes, we carried out a set of tsunami simulations considering some of the main known active crustal faults in the region: the Gorringe Bank (GBF), Marquês de Pombal (MPF), Horseshoe (HF), North Coral Patch (NCPF) and South Coral Patch (SCPF) thrust faults, and the Lineament South strike-slip fault. We started by considering for all of them relatively simple planar faults featuring with uniform slip distribution; we then used a more complex 3D fault geometry for the faults constrained with a large 2D multichannel seismic dataset (MPF, HF, NCPF, and SCPF); and finally, we used various heterogeneous slip distributions for the HF. Our results show that using more complex 3D fault geometries and slip distributions, the peak wave height at the coastline can double compared to simpler tsunami source scenarios from planar fault geometries. Existing tsunami hazard models in the region use homogeneous slip distributions on planar faults as initial conditions for tsunami simulations and therefore underestimate tsunami hazard. Complex 3D fault geometries and non-uniform slip distribution should be considered in future tsunami hazard updates. The tsunami simulations also support the finding that submarine canyons attenuate the wave height reaching the coastline, while submarine ridges and shallow shelves have the opposite effect, The authors are grateful for funding from MINECO through the project INSIGHT (CTM2015-70155-R), the project STRENGTH (PID2019-104668RB-I00), a MINECO FPI-2016 grant (BES-2016-078877) to Cristina S. Serra (ICM-CSIC), a MICINN “Juan de la Cierva-2017” grant (IJCI-2017-33838) to Sara Martinez-Loriente (ICM-CSIC), and from the Spanish government through the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S). We acknowledge the resources made available by the SISMOLAB-3D at INGV for the 3D fault modeling, Peer reviewed

20 pages, 19 figures, 1 table.-- Data Availability Statement: The original seismic images and maps used for this publication are available online (at https://doi.org/10.5281/zenodo.6350585, 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, Data collection and MC were supported by the project Geomargen-2 funded by REPSOL. The work was also supported by the EU project EMODnet-HRSM-2. Additional funding came from the Spanish Ministry of Science and Innovation projects: CTM2011-30400-C02-01 “HADES,” CGL2011-30005-C02-02 “SHAKE,” CTM2015-70155-R “INSIGHT,” PID2019-104668RB-I00 “STRENGTH,” CTM2015-71766-R “FRAME,” and PID2019-109559RB-I00 “ATLANTIS.” ICM has also had funding support of the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI), Peer reviewed

30 pages, 19 figures, 1 table.-- Data Availability Statement: The following key data set are used and made available in this paper: The new landslide database covering the Gulf of Cadiz is available through the following repository (Urgeles et al., 2021). The main outputs from the simulation, that is, those displayed in in Figures 9-12 and 14-19 are available through (Zengaffinen-Morris, 2022). The landslide model BingClaw has been published previously in the AGU journal Geophysical Research Letters, with the availability statement given in (Løvholt et al., 2017). Please note that the entire data set resulting from the model simulations, exceed 1 TB and is hence too large to place in a public repository. Hence, only the main outputs from the simulations are made available here, Probabilistic tsunami hazard analysis (PTHA) due to submarine landslides is much less developed than PTHA for earthquake sources. This is partly because of less constrained data available for quantifying source probability, and partly because of the lack of knowledge related to the tsunami generation process due to landslide dynamics. This study provides a basis for estimating the uncertainty related to landslide dynamics for PTHA from submarine landslides based on a new landslide database in the Gulf of Cadiz. The establishment of this new database is described herein. We use submarine landslide run-out statistics from this database to calibrate landslide parameters and related uncertainties employing the cohesive landslide model BingClaw. In turn, coupling the landslide motion to tsunami genesis is performed in order to characterize the inferred tsunami uncertainties. Important parameters that can explain the large tsunami uncertainties are the initial water depth of the landslide, the slope, the landslide volume, and the initial yield strength of the landslide material. Kinematic properties such as the initial landslide acceleration or the Froude number are found to strongly correlate with the tsunami-genesis. In this study, we show how matching numerical landslide models with observed run-out from past events in the field can give information about the uncertainty in their tsunami-genic strength. This can in turn be applied in future PTHA for spanning uncertainty ranges due to the landslide dynamics on tsunami-genesis, constrained by landslide run-out data, This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 721403. The Spanish “Ministerio de Ciencia e Innovación” and the European Regional Development Fund through grant CTM2015-70155-R (project INSIGHT) and Expert Analytics AS in Oslo are also acknowledged, Peer reviewed

10 pages, 8 figures.-- Data availability: The authors do not have permission to share data, Sediment undulations are widely distributed along continental shelf and slope worldwide. The driving mechanisms of undulations are crucial for assessing the long-term stability of continental slope, which, however, remain poorly understood. We used high-resolution 3D seismic data to investigate the internal architecture and origin of a field of seafloor and subsurface undulations along the slope of South China Sea (SCS). The undulations have narrow troughs and broad ridges. The reflection geometries in the troughs between undulations tend to be continuous and not offset by faults. These troughs terminate at different subsurface depths, commonly ranging from 50 to 400 ms in two-way travel time (TWTT) below the seafloor, often at locations related to subsurface geological structures, such as buried faults and steps within mass transport deposits (MTDs). These subsurface terminations therefore suggest that the undulations are probably depositional features not linked to creep-related basal detachment. The troughs between undulations display an absence of growth features, while the undulations increase in amplitude from base to top (characteristics that are also incompatible with gravitational deformation). Erosional and depositional features are commonly found in the undulations; thus, we interpret the narrow troughs between undulations to represent the areas where sediment-laden bottom currents undergo passage from supercritical to subcritical conditions. These troughs nucleated mostly from fault scarps and seafloor steps induced by past slope failures. Previous alternative interpretations report that these features originate from subsurface creep; alternatively, the present interpretation as sediment transport structures has significant implications for seafloor management and engineering projects, This study is supported by the National Key R&D Program of China (2022YFC3103800), National Natural Science Foundation of China (42276222, 42306092, and 52004047), Guangzhou Basic and Applied Basic Research Program (202201010488) , Development Fund of South China Sea Institute of Oceanology of the Chinese Academy of Sciences (SCSIO202207), Chongqing Municipal Scientific Research Institutions Performance Incentive and Guidance Project (cstc2022jxjl90001), and National Natural Science Foundation of ChongQing (CSTB2022NSCQ-MSX1406). RU thanks the “Ministerio de Ciencia, Innovación y Universidades, Spain” and the European Regional Development Fund for funding trough project INSIGHT (CTM2015-70155-R), With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed

16 pages, 7 figures, 2 tables, supplemental material https://doi.org/10.1130/B37954.1.-- Bathymetry data for the study area and the studied mud volcanoes, seismic data for the profiles GMV01, GMV03, INS2_Line13 and INS2_Line23, and a MATLAB-based pore water modeling code are archived in Zenodo https://doi.org/10.5281/zenodo.10393503), Mud volcanoes (MVs) are important gateways for fluid migration, particularly in subduction zones. We investigate five MVs in the Gulf of Cadiz and the Mediterranean Ridge, revealing underappreciated fluid pathways responsible for fluid expulsion. By utilizing pore water geochemistry, advection-diffusion modeling, and high-resolution seismic profiles, we trace fluid origins, quantify fluxes, and constrain migration pathways, focusing on the Ginsburg MV. The Cl-depleted summit fluids originate from clay dehydration within the Allochthonous Unit of the Gulf of Cadiz (AUGC) and are channeled by central conduits, reaching high advection velocities (2.8−15 cm/yr). The Cl-enriched moat fluids exhibit slower advection velocities (0.3 cm/yr) and show additional evaporite effects. To constrain moat fluid sources, fluid formation temperatures have been calculated using water isotopes and Mg-Li geothermometer. The resulting low temperatures suggest source depths atop the AUGC (∼0.8 kmbsf), consistent with seismic data across the Ginsburg MV (showing high-amplitude reflections at the same depths) but different from the summit sites, where the source is deeper within the AUGC (∼2.2 kmbsf). We relate moat seepage occurrence to fractures formed due to edifice subsidence, marked by stacked enhanced reflectors. Upon comparison with all analyzed MVs, we suggest that peripheral seepage of MV edifices is a widespread process that appears in a specific evolutionary stage, during which it represents an important component of fluid budget. This phenomenon, which has been observed in terrestrial MVs, is rarely described for their submarine counterparts but has wide biogeochemical implications for fluid budget in subduction zones and the sustenance of seafloor biological communities, Shuhui Xu is supported by the China Scholarship Council (CSC), and Walter Menapace is supported by the H2020 MSCA-IF-TURBOMUD project (grant 101018321). This research was funded in part by the Austrian Science Fund (FWF; grant M 3146-417 N) and projects CTM2015-70155-R (INSIGHT) and PID2020-114856RB-100 (ICEFLAME) funded by the Spanish Ministry of Science and Innovation (MCIN/ AEI/10.13039/501100011033). The European project EUMarineRobots (EUMR) is acknowledged for cofunding the M167 expedition (grant 731103), With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed