First AUV and ROV investigation of seismogenic faults in the Alboran Sea (Western Meditarranean)

In May-June 2015 we carried out the SHAKE cruise on board the RV “Sarmiento de Gamboa” the first in situ investigation using state-of-the-art underwater vehicles, the AUVs “AsterX” and “IdefX” (IFREMER, France) and the ROV “Max Rover” (HCMR, Greece). Here we present how these vehicles helped us to achieve our main goals to survey active seismogenic faults and associated structures of the Eastern Alboran Sea (Western Mediterranean).Peer Reviewe

Is The Iberian-African plates boundary well defined in the Alboran Basin of the Westernmost Mediterranean?

European Geosciences Union (EGU) General Assembly 2018, 8-13 April 2018, Vienna, Austria.-- 1 pageThe Alboran Basin (Westernmost Mediterranean) hosts the boundary between the Iberian and African plates. Traditionally, this boundary has been described as a wide deformation zone, in which the convergence is accommodated by several onshore-offshore tectonic structures. Extensional processes that led to the Alboran Basin formation took place from the Early to the Late Miocene, led by slab roll-back and slab tearing. During the Plio-Quaternary, the basin has been deformed due to the Iberia – Africa tectonic plates convergence, producing the contractive reorganization of some structures at the basin. In this study, we estimate the total slip accommodated by the most prominent tectonic structures in the area of Ear-liest Pliocene in age. We use Pre-Stack Depth Migrated sections of the crustal structure, that allow us to analyzed the real geometry of these structures at depth and to measure strain. We use the deformation-related geometry of strata and faults to estimate slip on the main faults. Results show that estimated total slip accommodated by the main fault system may be similar (with error bounds) to the estimated plate convergence value since the Messinian time (∼24 km). Thus, slip on that faults may have accommodated most of the Iberian – African plate convergence during the Plio-Quaternary, revealing that the contractive reorganization of the Alboran basin is focused on a few first-order structures that act as lithospheric boundaries, rather than widespread and diffuse along the entire basinPeer Reviewe

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

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

Compressional tectonic inversion of the Algero-Balearic basin: Latemost Miocene to present oblique convergence at the Palomares margin (Western Mediterranean)

Interpretation of new multichannel seismic reflection profiles indicates that the Palomares margin was formed by crustal-scale extension and coeval magmatic accretion during middle to late Miocene opening of the Algero-Balearic basin. The margin formed at the transition between thinned continental crust intruded by arc volcanism and back-arc oceanic crust. Deformation produced during the later positive inversion of the margin offshore and onshore is partitioned between ~N50°E striking reverse faults and associated folds like the Sierra Cabrera and Abubacer anticlines and N10–20°E sinistral strike-slip faults like Palomares and Terreros faults. Parametric subbottom profiles and multibeam bathymetry offshore, structural analysis, available GPS geodetic displacement data, and earthquake focal mechanisms jointly indicate that tectonic inversion of the Palomares margin is currently active. The Palomares margin shows a structural pattern comparable to the north Maghrebian margins where Africa-Eurasia plate convergence is accommodated by NE-SW reverse faults, NNW-SSE sinistral faults, and WNW-ESE dextral ones. Contractive structures at this margin contribute to the general inversion of the Western Mediterranean since ~7 Ma, coeval to inversion at the Algerian margin. Shortening at the Alboran ridge and Al-Idrisi faults occurred later, since 5 Ma, indicating a westward propagation of the compressional inversion of the Western Mediterranean

Tsunami hazards in the Catalan Coast, a low-intensity seismic activity area

The final publication is available at Springer via http://dx.doi.org/10.1007/s11069-017-2918-zThe potential impacts of tsunamis along the Catalan Coast (NW Mediterranean) are analysed using numerical modelling. The region is characterized by moderate to low seismic activity and by moderate- to low-magnitude earthquakes. However, the occurrence of historical strong earthquakes and the location of several active offshore faults in front of the coast suggest that the possibility of an earthquake-triggered tsunami is not negligible although of low probability. Up to five faults have been identified to generate tsunamis, being the highest associated possible seismic magnitudes of up to 7.6. Coastal flooding and port agitation are characterized using the Worst-case Credible Tsunami Scenario Analysis approach. The results show a multiple fault source contribution to tsunami hazard. The shelf dimensions and the existence of submerged canyons control the tsunami propagation. In wide shelves, waves travelling offshore may become trapped by refraction causing the wave energy to reach the coastline at some distance from the origin. The free surface water elevation increases at the head of the canyons due to the sharp depth gradients. The effects of potential tsunamis would be very harmful in low-lying coastal stretches, such as deltas, with a high population concentration, assets and infrastructures. The Ebro delta appears to be the most exposed coast, and about the 20% of the delta surface is prone to flooding due to its extremely low-lying nature. The activity at Barcelona port will be severely affected by inflow backflow current at the entrance of up to 2 m/s.Peer ReviewedPostprint (author's final draft

Alhama de Murcia slip rate based on paleoseismology and a morphotectonic analysis

Se calcula la velocidad de desplazamiento de la falla de Alhama de Murcia mediante la aplicación de dos técnicas: a) la paleosismología y b) el análisis morfotectónico. Estas metodologías basan el cálculo en la velocidad en la dislocación tectónica de un elemento lineal de edad conocida. Se han excavado trincheras 3D en el segmento Lorca-Totana con el fin de identificar y medir la dislocación de un paleocanal enterrado. La edad del canal ha sido delimitada gracias a dataciones de OSL, radiocarbono y series del uranio aplicadas a pequeñas cantidades de carbonato pedogénico. La velocidad total obtenida es 0.9 mm/a. En la terminación sur de la falla (segmento Goñar-Lorca) se han analizado ocho canales dislocados en superficie. Las edades máximas de estos canales (edad de la superficie en la que se encajan) se han aproximado gracias a dataciones publicadas basadas en la termoluminiscencia, junto con nuevas dataciones de carbonato pedogénico. La velocidad lateral mínima obtenida con esta metodología es de 1.7-1.6 mm/a. Estos valores, coincidentes con los de las trincheras 3D y mayores a los obtenidos hasta la fecha, reafirman la falla de Alhama de Murcia como una de las más activas de la Zona de Cizalla de las Béticas Orientales.We calculated the slip rate of the Alhama de Murcia fault by means of two techniques: a) paleoseismology, and b) a morphotectonic analysis. These methodologies measure the offset of a linear feature whose age is known. In the Lorca-Totana segment of the fault, we carried out a three-dimensional trenching campaign to identify and measure the offset of a buried paleochannel. The age of the paleochannel was constrained by new approaches of OSL, radiocarbon and U-series applied to small amounts of pedogenic carbonate datings. The mean net slip rate obtained is 0.9 mm/a. In the southernmost termination of the fault (Goñar-Lorca segment), we analysed eight offset channels in surface. The maximum ages of the channels (age of the surface in which they are entrenched) were estimated in base of previous geomorphological maps and of published ages (thermoluminescence) together with new datings of pedogenic carbonate. The minimum lateral slip rate for the fault in this area is 1.7-1.6 mm/a. These slip rate values position the Alhama de Murcia fault as one of the most active faults in the Eastern Betics Shear Zone.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Economía y Competitividad (MINECO)Generalitat de Catalunyapu