Wide-angle reflection and refraction seismic profile from the outer part of the gulf of Cadiz: nearest-seis cruise.

We will explain the first interpretations from a marine refraction and wide-angle reflection seismic profile acquired in the outer part of the Gulf of Cadiz in November 2008, in the framework of the Nearest-Seis cruise.Peer Reviewe

Configuration of geological domains and geodynamic evolution of the Africa-Eurasia plate boundary off SW Iberia revisited based on seismic velocity and density models

European Geosciences Union General Assembly 2015 (EGU2015), 12-17 April 2015, Vienna, Austria.-- 1 pageWe present a new classification of geological (basement) domains at the Africa-Eurasia plate boundary offshore SW Iberia, together with a regional geodynamic reconstruction spanning from the Mesozoic extension to the Neogene-to-present-day convergence. It is based on seismic velocity and density models along two regional wide- angle seismic transects, one running NW-SE from the Tagus to the Seine abyssal plains, and the other running N-S from S Portugal to the Seine Abyssal Plain, combined with previously available information. The seismic velocity and density structure at the Seine Abyssal Plain and the internal Gulf of Cadiz indicates the presence of a highly heterogeneous oceanic crust, similar to that described in ultra-slow spreading centers, whereas in the Horseshoe and Tagus abyssal plains, the basement structure resembles that of exhumed mantle sections identified in the Northern Atlantic margin. The integration of all this new information allows defining the presence of three oceanic domains off SW Iberia: (1) the Seine Abyssal Plain domain, generated during the first stages of slow seafloor spreading in the NE segment of the Central Atlantic (Early Jurassic); (2) the Gulf of Cadiz domain, made of oceanic crust generated in the Alpine-Tethys spreading system between Iberia and Africa, which was coeval with the formation of the Seine Abyssal Plain domain and lasted up to the North Atlantic continental break-up (Late Jurassic); and (3) the Gorringe Bank domain, mainly made of rocks exhumed from the mantle with little synchronous magmatism, which formed during the first stages of North Atlantic opening (Early Cretaceous). Our models suggest that the Seine Abyssal Plain and Gulf of Cadiz domains are separated by the Lineament South strike-slip fault, whereas the Gulf of Cadiz and Gorringe Bank domains appear to be limited by a deep thrust fault located at the center of the Horseshoe Abyssal Plain, which coincides with the seismicity cluster nucleated in the middle of the plain that shows moment tensor solutions of reverse faulting at depths of 40–60 km. The formation and evolution of these three domains during the Mesozoic is key to understand the sequence of events that occurred during the first stages of opening of the Northern Atlantic and its connection and interplay with the Western Mediterranean basinPeer Reviewe

Seismic and gravity constraints on the nature of the basement in the Africa-Eurasia plate boundary: New insights for the geodynamic evolution of the SW Iberian margin

We present a new classification of geological domains at the Africa-Eurasia plate boundary off SW Iberia, together with a regional geodynamic reconstruction spanning from the Mesozoic extension to the Neogene-to-present-day convergence. It is based on seismic velocity and density models along a new transect running from the Horseshoe to the Seine abyssal plains, which is combined with previously available geophysical models from the region. The basement velocity structure at the Seine Abyssal Plain indicates the presence of a highly heterogeneous, thin oceanic crust with local high-velocity anomalies possibly representing zones related to the presence of ultramafic rocks. The integration of this model with previous ones reveals the presence of three oceanic domains offshore SW Iberia: (1) the Seine Abyssal Plain domain, generated during the first stages of slow seafloor spreading in the NE Central Atlantic (Early Jurassic); (2) the Gulf of Cadiz domain, made of oceanic crust generated in the Alpine-Tethys spreading system between Iberia and Africa, which was coeval with the formation of the Seine Abyssal Plain domain and lasted up to the North Atlantic continental breakup (Late Jurassic); and (3) the Gorringe Bank domain, made of exhumed mantle rocks, which formed during the first stages of North Atlantic opening. Our models suggest that the Seine Abyssal Plain and Gulf of Cadiz domains are separated by the Lineament South strike-slip fault, whereas the Gulf of Cadiz and Gorringe Bank domains appear to be limited by a deep thrust fault located at the center of the Horseshoe Abyssal Plain

Processing and interpretation of multichannel seismic reflection data ( SWIN-06 cruise): from the horsehoe to seine abyssal plains (Gulf of Cadiz)

Martech 2007 International Workshop on Marine Technology, 15-16 november 2007, Vilanova i la Geltrú, Spain.-- 2 pages, 1 figureThe authors acknowledge the support of the SWIM project (REN2002-11234- E-MAR), National project EVENT (CGL 2006-12861-C02-02) and the EU-NEAREST project (Ref. 037110)Peer reviewe

Acoustic and seismic imaging of the Adra Fault (NE Alboran Sea): in search of the source of the 1910 Adra earthquake

13 pages, 7 figures, 1 tableRecently acquired swath-bathymetry data and high-resolution seismic reflection profiles offshore Adra (Almería, Spain) reveal the surficial expression of a NW–SE trending 20 km-long fault, which we termed the Adra Fault. Seismic imaging across the structure depicts a sub-vertical fault reaching the seafloor surface and slightly dipping to the NE showing an along-axis structural variability. Our new data suggest normal displacement of the uppermost units with probably a lateral component. Radiocarbon dating of a gravity core located in the area indicates that seafloor sediments are of Holocene age, suggesting present-day tectonic activity. The NE Alboran Sea area is characterized by significant low-magnitude earthquakes and by historical records of moderate magnitude, such as the Mw = 6.1 1910 Adra Earthquake. The location, dimension and kinematics of the Adra Fault agree with the fault solution and magnitude of the 1910 Adra Earthquake, whose moment tensor analysis indicates normal-dextral motion. The fault seismic parameters indicate that the Adra Fault is a potential source of large magnitude (Mw ≤ 6.5) earthquakes, which represents an unreported seismic hazard for the neighbouring coastal areasThe authors acknowledge the support of the Spanish Ministry of Science and Innovation (MICINN) through National Projects IMPULS (REN2003-05996MAR), EVENT (CGL2006-12861-C02-02) and SHAKE (CGL2011-30005-C02-02); Acciones Complementarias EVENT-SHELF (CTM 2008-03346-E/MAR) and SPARKER (CTM 2008-03208-E/MAR) and the ESF TopoEurope TOPOMED project (CGL2008-03474-E/BTE). We thank the captain, crew, scientific party and technical staff of the UTM-CSIC on board the Spanish R/V “Hesperides” and R/V “García del Cid” during the IMPULS and EVENT-SHELF cruises, respectively. We thank Fabrizio Pepe (Univ. Palermo) for his assistance in using the Geotrace software.We thank guest editor Hans Nelson, Carlos Marín Lechado and an anonymous referee for constructive comments and reviews. This work has been carried out within Grup de Recerca de la Generalitat de Catalunya B-CSI (2009 SGR 146)Peer reviewe

Editorial: Submarine Active Faults: From Regional Observations to Seismic Hazard Characterization

Since the beginning of the XXI Century, our society has witnessed a number of catastrophic earthquakes with devastating consequences (e.g., Sumatra 2004, Haiti 2010, Japan 2010, Nepal 2015, Italy 2009 and 2016). Localizing the active faults and understanding their earthquake history is key to improve modern probabilistic seismic hazard assessment (PSHA) and, thus, to mitigate the consequences of future events. Seismicity models to characterize the earthquake frequency in a region in PSHA studies have been traditionally based on archaeological, historical and instrumental earthquake records. However, the rapid advance of active tectonics and paleoseismological studies has resulted in the development of seismicity models for faults, since they allow characterizing the active faults, reconstructing their 3D geometry at depth, and determining their past earthquake history and seismic potential based on the interpretation of the geological record. Traditionally, active tectonics and paleoseismological research had been mainly conducted to study onshore active faults. However, the occurrence of the offshore Sumatra (2004) and Japan (2010) earthquakes and consequent tsunamis, which caused tens of thousands of casualties and extensive and severe damage and economic losses, have brought into sharp focus the need to better understand the geohazards related to submarine active faults. In the last few years, the availability of offshore geological and geophysical data at various scales (e.g., deep and shallow borehole, wide angle seismic profiles, tomography, 3D and 2D seismic reflection surveys, high resolution bathymetry or seafloor imaging) has allowed for a better definition of offshore fault systems. These studies focused on accurately constraining the kinematic, architecture and linkage of active faults, and, in some cases, identify recent earthquake ruptures or recognize and date individual events. In addition, underwater active tectonics and paleoseismological studies benefit from: (1) low erosional rates that preserve fault morphology and segmentation; (2) continuous sedimentation in time and space that allows for local and/or regional stratigraphic and chronostratigraphic correlations; (3) multiscale seafloor mapping and sub-seafloor seismic imaging; and 4) absence–or lowest amount–of human modification. This Research Topic includes fourteen published articles focused in the study of underwater active tectonic regions or active fault systems around the world (Figure 1). They use different datasets (i.e., bathymetry, seismicity from a local seismic network, sub-bottom profiling, reflection seismic profiles or sedimentary cores) to identify and characterize the seismic cycle of active faults using multidisciplinary approaches and innovative methodologies. The main goal of this Research Topic has been to show the present advance in underwater active tectonics and paleoseismology in order to improve our understanding about the seismic and tsunami hazard. Here we provide a short review of the contributions grouped by the main topics

Active deformation in old oceanic lithosphere and significance for earthquake hazard: Seismic imaging of the Coral Patch Ridge area and neighboring abyssal plains (SW Iberian Margin)

Martínez-Loriente, S. ... et al.-- 26 pages, 13 figures, 1 tableRecently acquired high-resolution multichannel seismic profiles together with bathymetric and sub-bottom profiler data from the external part of the Gulf of Cadiz (Iberia-Africa plate boundary) reveal active deformation involving old (Mesozoic) oceanic lithosphere. This area is located 180 km offshore the SW Iberian Peninsula and embraces the prominent NE-SW trending Coral Patch Ridge, and part of the surrounding deep Horseshoe and Seine abyssal plains. E-W trending dextral strike-slip faults showing surface deformation of flower-like structures predominate in the Horseshoe Abyssal Plain, whereas NE-SW trending compressive structures prevail in the Coral Patch Ridge and Seine Hills. Although the Coral Patch Ridge region is characterized by subdued seismic activity, the area is not free from seismic hazard. Most of the newly mapped faults correspond to active blind thrusts and strike-slip faults that are able to generate large magnitude earthquakes (Mw 7.2-8.4). This may represent a significant earthquake and tsunami hazard that has been overlooked so far. Key Points New active structures have been mapped in the Coral Patch Ridge area The newly mapped faults are able to generate large magnitude earthquakes (Mw>7) These new structures may represent a significant earthquake and tsunami hazard ©2013. American Geophysical Union. All Rights ReservedThe authors acknowledge the support of the Spanish Ministry of Science and Innovation (MICINN) through National Projects EVENT (CGL2006–12861-C02-02) and SHAKE (CGL2011–30005-C02-02); 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), the ESF TopoEurope TOPOMED project (CGL2008–03474-E/BTE), and the SWIMGLO project (PTDC/MAR/100522/2008). We also acknowledge funding from the MICINN through the ‘‘Ramon y Cajal’’ program (R. Bartolome) and from the CSIC through a JAE Pre-Doc fellowship (S. Martínez-Loriente)Peer Reviewe

Characterizing active faults and associated mass transport deposits in the South Iberian Margin (Alboran Sean and Gulf of Cadiz): on-fault and off-fault paleoseismic evidence

During the last years we have carried out successive high-resolution marine geological and geophysical surveys to investigate the seismic potential of the slow-moving seismogenic faults from the South Iberian Margin. Based on ,ultiscale acoustic mapping, sub-seafloor seismic imaging and dating methods we have characterized submarine fault systems with unprecedented resolution. We present primary paleoseismic evidence obtained by direct investigations of selected faults from theMediterranean Sea (i.e. Carboneras Fault, Bajo Segura Fault, Adra Fault) and the external part of the Gulf of Cadiz (i.e. Marques de Pombal Fault, Horseshoe Fault, Coral Patch Ridge Fault and SWIM lineaments). The obtained fault seismic parameters suggest that these faults are active and capable of generating large magnitude (Mw > 6) seismic events, representing an earthquake and tsunami hazard for the surrounding coastal areas. Secondary paleoseismic evidence in the SW Iberian Margin (based on landslides and turbidite deposits) yields a regional recurrence rate of large magnitude earthquake of 1800 - 2000 years

The crustal domains of the Alboran Basin (Western Mediterranean)

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 sub‐basins, and d) the oceanic crust in the transition towards 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

A tribute to Marie Tharp: Mapping the seafloor of back-arc basins, mid-ocean ridges, continental margins and plate boundaries

European Geosciences Union (EGU) General Assembly 2020, 4-8 May 2020Marie 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 technologie