Marine Technology Workshop (Martech05), 17-18 November 2005, Vilanova i la Geltrú, Barcelona.-- 2 pages, 1 figurePeer Reviewe

Díez Tagarró, Susana

Gràcia, Eulàlia

Gutscher, Marc-André

Matias, L.

Mulder, Thierry

Somoza, Luis

Terrinha, Pedro

Digital.CSIC

Instrumentation ViewPoint. Autumn 200542Lebreiro, S.M., McCave, I.N., Weaver, P.P.E.,Late quaternary turbidite emplacement on theHorseshoe Abyssal Plain (Iberian Margin), J.Sed. Res., 67, 5, pp 856-870. 1997.Sartori, R., L. Torelli, N. Zitellini, D. Peis, E.Lodolo, Eastern segment of the Azores-Gibraltarline (central-eastern Atlantic): An oceanic plateboundary with dif fuse compressionaldeformation, Geology, 22, pp 555-558. 1994.Stich, D., Mancilla, F., Morales, J., Crust-mantlecoupling in the Gulf of Cadiz (SW Iberia),Geophys .  Res .  Le t t . ,  32 ,  L13306,doi:10.1029/2005GL023098. 2005Terrinha, P., Pinheiro, L.M., Henriet, J.P., Matias,L., Ivanov, M.K., Monteiro, J.H., Akhmetzhanov,A., Volkonskaya, A., Cunha, T., Shaskin, P.,Rovere, M, Tsunamigenic-seismogenicstructures, neotectonics, sedimentary processesand slope instability on the southwest PortugueseMargin, Mar. Geol., 195(1-4), pp 55-73. 2003.Zitellini, N., Mendes Victor, L., Córdoba, D.,Dañobeitia, J.J., Nicolich, R., Pellis, G., Ribeiro,A., Sartori, R., Torelli, L., BIGSETS Team,Source of the 1755 Lisbon Earthquake andTsunami Investigated, EOS Trans. AGU, 82, pp285-291. 2001.Bathymetric map of the Gulf of Cadiz, NE Atlantic Ocean: The SWIMmultibeam compilationS. Diez1, E. Gràcia1, M.A. Gutscher2, L. Matias3, T. Mulder4, P. Terrinha5, L. Somoza6, N.2Institut Universitaire Européen de la Mer (IUEM), UMR 6538 Domaines Océaniques, Pl. N. Copernic,29280 Plouzané, France3Centro Geofísica da Universidade de Lisboa-CGUL, Campo Grande C8, 1749-016 Lisboa, Portugal4Dpt. Géologie et Océanographie, UMR 5805 EPOC – OASU, Université Bordeaux 1, Avenue desFacultés, 33405 Talence, France5Laboratorio de Tectonofisica e Tectonica Experimental (LATTEX), Campo Grande C6, 1749-016,Lisboa, Portugal.6Instituto Geológico y Minero de España (IGME), Ríos Rosas 23 28003 Madrid, Spain7ISMAR,CNR, Via Gobetti 101, 40129 Bologna, Italy8IAMC-Geomare sud, CNR, Calata Porta di Massa, 80133, Napoli, Italy9Renard Centre of Marine Geology, Dpt. Geology and Soil Science, Ghent University, Krijgslaan 281s.8, B-9000 Gent, Belgium1. IntroductionThe Gulf of Cadiz, located at the convergentboundary between the European and AfricanPlates, is characterized by a significant andwidespread seismicity This area is also thesource of the largest event occurred duringhistorical times in Western Europe, the 1755Lisbon Earthquake and Tsunami [1]. Since the 1990s the Gulf of Cadiz has beenthe subject of numerous geological andgeophysical surveys, mainly based onmultibeam, sidescan sonar, high-resolution andmultichannel seismics, and sampling. The aimhas been unravelling the complex geodynamichistory of the Gulf of Cadiz, to characterize thedeep structure, and to identify active tectonicsources in the region.We focus on recently acquired multibeam datato present a new bathymetric compilation map.2. Swath Bathymetric Data and Generationof a Digital Terrain Model (DTM)The compilation of the deep multibeambathymetric data in the Gulf of Cadiz include,as essential components, the 100 m gridsacquired during the following cruises: TASYO-2000  PARSIFAL-2000, CADISAR-2001, HITS-2001, PICABIA-2003, MATESPRO-2004,CADISAR2-2004, DELILA-2004, DELSIS-2005,and SWIM2-2005.Additional data on specific localities, has beenprovided by J.P. Henriet, G. De Alteriis teams,and SISMER database. The multibeam systemsused to survey the seafloor are Simrad EM3000and EM1000 for shallow areas, and SimradEM300, EM12S, EM120 and Reson Seabat8150 for intermediate to deep waters.Figure 1. Bathymetric compilation mapInstrumentation ViewPoint.Autumn 200543The SWIM compilation includes data located inthe area between 34ºN and 38ºN and between12.5ºW and 5.5ºW (Fig. 1). For data processingand merging, we have used the CARAIBESsystem [2], a complete submarine mappingsoftware developed by IFREMER to process datafrom multibeam echo-sounders (bathymetry andacoustic backscatter).The main steps during data processing includequality control, validation and data filtering. Afterfiltering, bathymetric data is interpolated at nodesof a regular-spacing grid in order to get a finalDTM [3].In the compilation map the swath bathymetriccolour grid is overlaid by contours at 200-m intervalfrom the “General bathymetric chart of the oceans”at 1 minute grid (1852 m) (GEBCO, 2004) [4].For the land areas, we used digital grids releasedby the Seamless Shuttle Radar TopographyMission (SRTM-3) at 3 arc second interval (~90m). Coastlines are extracted from the full-resolutionGMT database.3. ConclusionsThe SWIM bathymetric compilation illustrates themain physiographic features of the Gulf of Cadiz,such as the talus, dominated by deeply incisedsubmarine canyons; the central part dominatedby faulted tectonic blocks (i.e. Marques de Pombal,Guadalquivir Bank) and mud volcanoes anddiapirs of the accretionary wedge; and the oceanicexternal areas, comprising the Horseshoe AbyssalPlain and Gorringe Bank. The map reveals activemorphostructures of tectonic, sedimentary andbiogeochemical origin imprinted on the seafloor.In particular, this cartography allows us to identifyseafloor ruptures of active faults, potential sourcesof large seismic events in the Gulf of Cadiz. Thepotential sources of the Great 1755 LisbonEarthquake and Tsunami, i.e. Marques de Pombal,Horseshoe, and Pereira da Souza Faults,Guadalquivir Bank, and Gibraltar arc accretionarywedge [5-6-7-8-9-10], are included in this newbathymetric map, which will help to elucidatebetween the different tectonic sources suggested.4. References[1] Baptista, M.A., Miranda, P.M.A., Miranda, J.M.,Mendes Victor, L., Constrains on the source ofthe 1755 Lisbon Tsunami inferred from numericalmodelling of historical data, J. Geodynamics, 25,pp 159-174. 1998. [2] Bourillet, J. F., Edy, C., Rambert, F., Satra,C. and Loubrieu, B., . Swath Mapping SystemProcessing: Bathymetry and Cartograph, MarineGeophysical Researches, 18, 487-506. 1996.[3] Diez, S., and Gràcia, E., Submarine Mappingusing Multibeam Bathymetry and AcousticBackscatter: I l luminating the Seafloor.Instrumentation Viewpoint, 3, Spring 2005, p. 10-14. 2005.[4] GEBCO, 2004. Development of the GEBCOworld Bathymetry grid, GEBCO website.[5] Gutscher M.-A., J. Malod, J.-P. Rehault, I.Contrucci, F. Klingelhoefer, W. Spakman, L.Mendes-Victor,. Evidence for active subductionbeneath Gibraltar? Geology; v. 30; no. 12; p.1071–1074. 2002.[6] Baptista, M.A., Miranda, J.M., Chierici, F.,and Zitellini, N.. New study of the 1755earthquake source based on multichannelseismic survey data and tsunami modeling.Natural Hazards and Earth System Sciences,3, 333-340. 2003.[7] Gràcia, E., Dañobeitia, J.J., Vergés, J.,PARSIFAL, Mapping active faults offshorePortugal (36º-38ºN): Implications for seismichazard assessment in the SW Iberian Margin,Geology 31, pp 83-86. 2003a.[8] Terrinha, P., Pinheiro, L.M., Henriet, J.P.,Matias, L., Ivanov, M.K., Monteiro, J.H.,Akhmetzhanov, A., Volkonskaya, A., Cunha,T., Shaskin, P., Rovere, M, Tsunamigenic-seismogenic structures, neotectonics,sedimentary processes and slope instability onthe southwest Portuguese Margin, Mar. Geol.,195(1-4), pp 55-73. 2003.[9] Zitellini, N., Mendes, L.A., Cordoba, D.,Danobeitia, J., Nicolich, R., Pellis, G., Ribeiro,A., Sartori, R., Torelli, L., and BIGSETS Team,Source of 1755 Lisbon Earthquake and TsunamiInvestigated. EOS Trans. AGU, 82, Number 26.2001.[10] Zitellini, N., Rovere, M., Terrinha, P., Chierici,F., Matias, L., and BIGSETS Team, Neogenethrough Quaternary tectonic reactivation of SWIberian Passive Margin. Pure Appl. Geophys.,161,565-587. 2004.

Bathymetric map of the Gulf of Cadiz, NE Atlantic Ocean: The SWIM multibeam compilation

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