Search

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

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)

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)

European Geosciences Union (EGU) General Assembly 2020, 4-8 May 2020, 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 driven by glacial – interglacial period alternation that influenced the hydrodynamic regime of the MOW. By deriving the depositional history of sand in the Alentejo basin, we are able to correlate directly the influence that climatic cycles had on the MOW activity. Furthermore, by interpreting new multi-channel seismic profiles we have been able to derive a detailed facies characterization of the uppermost part of the Gulf of Cadiz. An accurate definition of sand distribution along slope plays an important role in evaluating the stability of the slope itself, e.g. to understand if the sediments may be subjected to excess pore pressure generation. As sand distribution is a direct function of the bottom-current transport capacity, the ultimate goal of this study is to understand how climate variations can affect the stability of submarine slope by depositing contourite-related sand, This project has received funding from the European Union’sHorizon 2020 research and innovation programme under grantagreement No 721403

European Geosciences Union (EGU) General Assembly 2020, 4-8 May 2020, 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, 1994, 2004 and 2016. In addition, the Gulf of Cadiz-Alboran Sea area is compartmentalized in different crustal domains, bounded by active strike-slip fault systems. We adopted a multi-scale approach, including morphological analysis of shipboard multibeam bathymetry, near-bottom bathymetry obtained with Autonomous Underwater Vehicles (AUVs) at a resolution of 1-2 m, and medium to deep penetration multi-channel seismic (MCS) data. Finally, we will also show a couple of videos from recent marine cruises in the Gibraltar Arc (SHAKE-2015 and INSIGHT-2018), both using state-of-the-art high-resolution marine technologies

European Geosciences Union (EGU) General Assembly 2020, 4-8 May 2020, 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 traces, which are not continuous and show a set of crests and troughs of a width of 100s of meters. The deformation associated to LS span’s about 2-3 km at the seafloor cutting the seismo-stratigraphic sequences, including the Quaternary unit, which reach up to the seafloor. According to the scaling-law of Leonard (2014), the maximum magnitude earthquake that LS can generate is up to Mw 7.9. An earthquake of this magnitude can produce a tsunami that may affect the SW Iberian Peninsula, with a wave amplitude higher than 1 m. Eventually, the LS may generate a significant earthquake and tsunami along the Portuguese, Spanish and Moroccan coasts