New marine infrastructures and technology development, application to Tsunami Early Warning System: EU Research Infrastructure EMSO European Multidisciplinary Seafloor and Water-Column Observatory

Presentación para la Jornada Técnica sobre el riesgo de maremotos: Proyecto de la Directriz básica de protección civil ante el riesgo de maremotos, 29 y 30 de septiembre de 2014, Rivas-Vaciamadrid, Madrid.-- 29 pagesPeer 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

Seismic structure of the northern continental margin of Spain from ESCIN deep seismic profiles

By the end of the Carboniferous, the crust of the continental shelf in northwestern Spain was made up of deeply rooted structures related to the Variscan collision. From Permian to Triassic times the tectonic setting had changed to mainly extensional and the northern Iberian continental margin underwent rifting during Late Jurassic-Early Cretaceous times, along with sea-floor spreading and the opening of the Bay of Biscay until the Late Cretaceous. Subsequently, the northern Iberian margin was active during the north-south convergence of Eurasia and Iberia in the Tertiary. A multichannel seismic experiment, consisting of two profiles, one north-south (ESCIN-4) crossing the platform margin offshore Asturias, and another (ESCIN-3) crossing the platform margin to the northwest of Galicia, was designed to study the structure of the northern Iberian margin. The ESCIN-4 stacked section reveals inverted structures in the upper crust within the Le Danois Basin. North of the steep continental slope, ESCIN-4 shows a thick sedimentary package from 6 to 9.5 s, two-way travel time (TWT). Within this latter package, a 40-km-long, north-tapering wedge of inclined, mainly south-dipping reflections is thought to represent a buried, Alpine-age accretionary prism. In the north western part of the ESCIN-3 (ESCIN-3-1) stacked section, horizontal reflections from 6.5 to 8.5 s correspond to an undisturbed package of sediments lying above oceanic-type basement. In this part of the line, a few kilometres long, strong horizontal reflection at 11.2 s within the basement may represent an oceanic Moho reflection. Also, a band of reflections dips gently towards the southeast, from the base of the gently dipping continental slope. The part of ESCIN-3 line that runs parallel to the NW-Galicia coast (ESCIN-3-2), is characterized by bright, continuous lower crustal reflections from 8 to 10 s. Beneath the lower crustal reflectivity, a band of strong reflections dips gently toward the southwest from 10 to 13.5 s. The part of ESCIN-3 that parallels the northern margin (ESCIN 3-3), shows good reflectivity in all levels. Upper crustal reflections image the sedimentary fill of probable Mesozoic to recent basins. Mid-crustal reflectivity is characterized by dipping reflections until 8 s that are probably related to compressional Variscan features. The lower crustal level shows 'layered' reflections between 8 and 12 s. Dipping reflections are found below the continental Moho.J. Alvarez-Marrón held a post-doc research grant from the Ministry of Education and Science of Spain. The ESCI-N program was sponsored by the Spanish agencies CICYT (project GEO 90-0660) and FICYT, and STRIDE Program of the EU.Peer Reviewe

Identificación de riesgos geoambientales y su valoración en la zona de hundimiento del buque Prestige

Potential geological hazard assessment has been carried out in the area where the Prestige vessel was sunk using a broad database that comprises: multibeam, high and ultra-high resolution seismic profiles, gravity cores, onland seismicity stations and Ocean Bottom Seismometers (OBS). The main results of this study indicate that among the geologic factors that can be considered as potential hazards, four main categories can be differentiated based on their origin: morphologic, sedimentary, tectonic, and seismicity. Hazards of morphologic origin include steep gradients; the morphologic features suggest the occurrence of mass-wasting instabilities. Hazards of sedimentary origin also includes the occurrence of slope instability processes in form of single slides and a great variety of erosive and depositional gravity flows (debris and turbidity flows). Hazards of tectonic and seismic origin are important because the sinking area straddles the Calida Bank which is a structural seamount with a moderate tectonic activity that results in a latent seismicity of low to moderate magnitude. The interaction of these factors leads to consider to the risk as medium, and the degree of exposure of the bow and stern as high. Several general and specific recommendations are made in order to increase the geological and geophysics knowledgement in the Prestige sinking area and Spanish continental margins and deep sea areas. These recommendations also should be used to elaborate the options for reducing the hazard and loss

Estudio mediante sísmica de reflexión de un grupo de estructuras submarinas situadas al Norte y Sur del archipelago Canario

Queremos agradecer la ayuda prestada por la tripulacidn del buque oceanográfico holandes M.V. Tyro, asi como los comentarios críticos de J.I. Diaz, Marcel-li Farrhn, C. R. Ranero y la ayuda en la parte gráfica de E. Clavero.[ES] El Archipiélago Canario es un complejo volcánico intraplaca situado al oeste del margen occidental africano. La realización de una campaña de sísmica de reflexión ha permitido estudiar un grupo de estructuras submarinas asociadas al Archipiélago Canario. Este estudio ha confirmado la existencia de alineaciones estructurales (Dorsal Canaria) de direcci6n NNE-SSW al Norte del Archipiélago, con un acimut de 51' y con una disposición en escalón. Sin embargo, no se han encontrado conexiones subyacentes entre estas estructuras y las Islas Canarias, a pesar de que las propias alineaciones podrían sugerir la existencia de fallas en el basamento oceánico. Algunos edificios volcánicos como las Islas Salvajes, La Complutense y la Topera pueden definirse como independientes por no encontrase en la alineación de la Dorsal Canaria. Por otra parte, se han localizado pequeñas cuencas sedimentarias en los flancos de las elevaciones submarinas que ponen de manifiesto la importancia de la flexura ocasionada por tales cargas. Las características de la sedimentaci6n cambian gradualmente de la zona occidental a la oriental, donde la influencia de los procesos que se desarrollan en el margen continental africano controlan de manera importante tanto la morfologia de los depósitos como el espesor de sedimentos. La correlaci6n de los datos sísmicos con sondeos próximos (DSDP) sugiere que el volcanismo submarino al norte del Archiélago probablemente comenzó en el Paleógeno y ha continuado hasta nuestros días de manera intermitente, confirmindose la existencia de una reactivación importante en el Mioceno medio. Mientras que el inicio del volcanismo al sur del Archipiélago es de edad miocena.[EN] The Canarian Archipelago is an intraplate volcanic feature situated on the Western African Margin. A seismic reflection reconnaissance was carried out in the surrounding waters of the Canarian Archipelago to study a series of submarine structures. A linear trend NNE-SSW for the submarine structures (Canary Ridge) was confirmed, exhibiting an echelon morphology with an azimuth of 51". No indication of subbottom structures have been observed connectlng these seamounts with the Canary Islands, despite that the lineation suggests the existence of faulting in the oceanic basement. Some independent volcanic highs are found, like I. Salvajes, La Complutense and La Topera. Significant sedimentary basins have been found on the flanks of the seamounts, pointed out the importance of the flexure produced by the seamounts. The sedimentation pattern changes gradually westward and the proximity of the continental margin greatly affects the sedimentary thicknesses on the eastern side. There is evidence from the correlation of seismic-reflections with near DSDP holes, that the volcanic activity north of the Archipelago, could not have started before Paleogene and has been episodic through time with some reactivation at least on Middle Miocene. South of the Archipelago the starting of the volcanic activity is younger (= Miocene).Este trabajo se ha llavado a cabo gracias a una beca de intercambio, obtenida por el primer autor, entre el Consejo Superior de Investigaciones Científicas y el Vening Meinesz Laboratorium de la Universidad de Utrecht. La campaña oceanogrhfica ha sido subvencionada por el Zuiver Wetenschappelijk Onderzoek.Peer reviewe

Magmatic underplating in the Canary Archipelago

15 pages, 12 figuresThe location of the Canary Archipelago, at the east edge of the North Atlantic, a few hundred kilometres from the West African coast, has for years posed a serious difficulty in understanding the complex interaction between long-lasting volcanic activity and one of the oldest seafloor basements (>150 Ma) on earth. Many different hypotheses have been proposed in the last two decades to understand the genesis of the Canary Archipelago. There is an increasing acceptance to explain the archipelago as the product of the slow passage of the African plate over a mantle hotspot. In rival tectonic models, stretching and thinning of the lithosphere would determine the islands as independent volcanic blocks. We review recent geophysical and geological evidence supporting a mantle plume origin for the Canary Islands, based on the recognition of crustal thickening by mafic intrusions produced by the interaction between the mantle plume and the old oceanic lithosphere beneath the Canary Archipelago. © 2000 Elsevier Science B.V. All rights reserve

The Canary Islands swell: A coherence analysis of bathymetry and gravity

10 pages, 7 figures, 1 tableThe Canary Archipelago is an intraplate volcanic chain, located near the West African continental margin, emplaced on old oceanic lithosphere of Jurassic age, with an extended volcanic activity since Middle Miocene. The adjacent seafloor does not show the broad oceanic swell usually observed in hotspot-generated oceanic islands. However, the observation of a noticeable depth anomaly in the basement west of the Canaries might indicate that the swell is masked by a thick sedimentary cover and the influence of the Canarian volcanism. We use a spectral approach, based on coherence analyse, to determine the swell and its compensation mechanism. The coherence between gravity and topography indicates that the swell is caused by a subsurface load correlated with the surface volcanic load. The residual gravity/geoid anomaly indicates that the subsurface load extends 600 km SSW and 800 km N and NNE of the islands. We used computed depth anomalies from available deep seismic profiles to constrain the extent and amplitude of the basement uplift caused by a relatively low-density anomaly within the lithospheric mantle, and coherence analysis to constrain the elastic thickness of the lithosphere (Tc) and the compensation depth of the swell. Depth anomalies and coherence are well simulated with Tc=28-36 km, compensation depth of 40-65 km, and a negative density contrast within the lithosphere of ∼33 kg m-3. The density contrast corresponds to a temperature increment of ∼325°C, which we interpret to be partially maintained by a low-viscosity convective layer in the lowermost lithosphere, and which probably involves the shallower parts of the asthenosphere. This interpretation does not require a significant rejuvenation of the mechanical properties of the lithospher

Magnetic anomalies in the canary basin and the Mesozoic evolution of the central North Atlantic

23 pages, 16 figures, 1 tableThe data from a recent magnetic compilation by Verhoef et al. (1991) off west Africa were used in combination with data in the western Atlantic to review the Mesozoic plate kinematic evolution of the central North Atlantic. The magnetic profile data were analyzed to identify the M-series sea floor spreading anomalies on the African plate. Oceanic fracture zones were identified from magnetic anomalies and seismic and gravity measurements. The identified sea floor spreading anomalies on the African plate were combined with those on the North American plate to calculate reconstruction poles for this part of the central Atlantic. The total separation poles derived in this paper describe a smooth curve, suggesting that the motion of the pole through time was continuous. Although the new sea floor spreading history differs only slightly from the one presented by Klitgord and Schouten (1986), it predicts smoother flowlines. On the other hand, the sea floor spreading history as depicted by the flowlines for the eastern central Atlantic deviates substantially from that of Sundvik and Larson (1988). A revised spreading history is also presented for the Cretaceous Magnetic Quiet Zone, where large changes in spreading direction occurred, that can not be resolved when fitting magnetic isochrons only, but which are evident from fracture zone traces and directions of sea floor spreading topography. © 1992 Kluwer Academic Publisher

Mapping the Moho in the Iberian Mediterranean Margin by Multicoverage Processing and Merging of Wide-Angle and Near-Vertical Reflection Data

Nonnal incidence seismic reflection data have been collected recently in the Iberian Mediterranean margin within the Spanish ESCI programme. The experiments include in-line recordings onshore of marine profiles, and provide coincident small and large-offset multicoverage of complex areas such as the onshore/offshore transition, where classic stacked images of the vertical reflectivity lack resolution and hamper a thorough comprehension of the structure and its lateral evolution. We obtained coherent and enhanced crustal images by developing a wide-angle multichannel processing analogous to the near-vertical conventional one and merging the final stacked and migrated sections. All the wide-angle sections generated show clear images of the Moho reflectivity. In the Valencia trough, a combined transect documents the lateral evolution of the deep crustal reflectivity across strike of structures. A steady thinning of the crust is revealed in the Iberian margin, from a depth of 32 km beneath the Catalap ranges up to 19 km depth at 60 km seawards. A similar thinning rate is observed on the Balearic flank. In the central part of the trough the Moho is imaged at constant depths around 16-17 km. The lower crustal reflectivity as well as the velocity-depth and gravity results indicate that the thinning is accomodated mainly by the lower crust. Underplating features reported in continental passive Atlantic margins are not supported here by the low velocities of 6.4-6.5 km/s found in the lower crust. In the central part of the BeticsAlboran domain the wide-angle stacked section suggest, in agreement with previous gravity interpretations, that the thin Alboran Sea crust extends beyond the shoreline, up to 10-15 km inland where a Moho jump down of about 3 s TWT marks the southernmost limit of the internal Betics thick crust. The strong stretching rates inferred from the present crustal images in the Iberian Mediterranean margin are to be related with the interaction of extensional processes within a convergent regime between the African and Iberian plates, or even with shear tectonics in the Betics-Alboran domain.The ESCI seismic programme is supported by the spanish "Plan Nacional de I+D". This work has been partially financed by CICYT projects n. GEO89-0858-E; GEO90-0733; GEO90-0617.Peer reviewe