Marine Technology Workshop (Martech05), 17-18 November 2005, Vilanova i la Geltrú, Barcelona.-- 2 pages, 1 figureThe authors are grateful for funding from MCYT Acción  Especial  HITS  (REN2000-2150-E), European Commission EASSS-III programme (HPRI-CT99-0047), European Large Scale Facility (HPRI-CT2001-00120)  and  Spanish  National Project  IMPULS  (REN2003-05996MAR)Peer Reviewe

Dañobeitia, Juan José

Díez Tagarró, Susana

Gràcia, Eulàlia

Pallàs, R.

Terrinha, Pedro

Vizcaino, A.

Pallàs, Raimon

Digital.CSIC

Instrumentation ViewPoint. Autumn 200544Active tectonic and sedimentary processes along the São VicenteCanyon (SW Iberian Margin): High-Resolution ImagingA. Vizcaino (1), E. Gràcia (1),  R. Pallàs (2),  P. Terrinha (3), S. Diez (4), J. Dañobeitia (1)and D, Masson (4)(1) Unitat de Tecnologia Marina (CMIMA) - CSIC, Barcelona, Spain,+34 93 2309500, alexis@utm.csic.es.(2) Facultat de Geologia, Universitat de Barcelona, Barcelona, Spain,(3) Faculdade de Lisboa, Dept. de Geologia, Lisboa, Portugal,(4) Challenger Div. Seafloor Processes, Southampton Oceanography Centre, United Kingdom1. IntroductionThe SW Iberian Margin hosts the present-dayboundary between the Eurasian and AfricanPlates. Plate convergence of 4 mm/yr isaccommodated over a large and diffusedeformation zone, characterized by significantand widespread seismic activity. The region isalso the source of the largest earthquakes andtsunamis in Western Europe, such as the 1755Lisbon event. One of the most prominentstructures in this margin is the São VicenteCanyon (SVC), a deeply carved long conduitlinking the Portuguese shelf and HorseshoeAbyssal Plain at 5000 m depth. The seafloormorphology and shallow structure of the  SVCwas the object of study as part of the HITScruise on board the Spanish RV Hespérides(September, 2001).2. Results and DiscussionWe present here our main results based on theanalyses and integration of the newly acquireddata: swath-bathymetry, TOBI sidescan sonarbackscatter and high-resolution seismics.The SVC is deeply incised in a large amplitudesyncline bounded by active structures (the SãoVicente Faults and Horseshoe Faults), assuggested by swarms of shallow to intermediateearthquakes and seafloor faulting ruptures. TheSVC is over 100 km long, 20 km wide and withmore than 1000 m of vertical relief on its highestpart. The canyon has asymmetric and rectilinearflanks following three main segments, fromNorth to South: the canyon head with a N030trend, the central part with a N045 direction,and the canyon mouth trending N-S. TheHorseshoe Fault, which delineates the eastflank of the SVC at the Horseshoe AbyssalPlain, follows a main N43 direction. The TOBIimage from the SVC shows a large variety ofacoustic facies illustrating different tectono-sedimentary processes. The canyon floor ishighly reflective and heterogeneous, whereareas of coarse-grained bedload with chaoticseismic facies co-exist with localized outcropsof bared stratified rock-strata. The canyon flanksare mainly dominated by homogenouslow reflectivity characteristic of hemipelagicsedimentation. However, high reflective areasand strong acoustic shadows are commontowards the middle part and base of the canyonflanks, corresponding to incised gullies, landslideheadscarps and mass wasting deposits..3. ConclusionsTectonic activity, submarine erosion andephemeral sediment transport draining to theHorseshoe Abyssal Plain (HAP) defines thepresent-day morphostructure of the SVC. Duringthe Holocene, the most likely mechanism oflandslide triggering in the SW Iberian Margin isseismic activity. Thus, the mass wastingprocesses (turbidites and debris flows) fillingthe HAP may give us valuable information ofthe earthquake event history of the margin,which we are also studying as part of the ESFFig. 1. Bathymetric map of the SW PortugueseMargin (contour 200 m). High-resolution swath-bathymetry survey is depicted in colour (Gràciaet al., 2003a). TOBI sidescan sonar data andpiston cores longer than 1m acquired in the areaare also located. Large filled circles correspondto the acquired CALYPSO giant piston corer sitesInstrumentation ViewPoint.Autumn 200545EuroMargins SWIM project.The authors are grateful for funding from MCYTAcción Especial HITS (REN2000-2150-E),European Commission EASSS-III programme(HPRI-CT99-0047), European Large Scale Facility(HPRI-CT2001-00120) and Spanish NationalProject IMPULS (REN2003-05996MAR).4. References [1] W.E. Smith, “Instrumentation”, Marcel Dekker,New York, 1998.[2] L.W. Hi, Evolutions in Electronics Engineering,Proc.  IMTC Meet ing,  Phoenix,  2005.[1] D.F., Argus, Gordon, R.G., De Mets, C. &S,Stein, Closure of the Africa-Eurasia-NorthAmerica Plate Motion Circuit and Tectonics ofthe Gloria Fault. Journal of Geophysical Research,94, B5: 5585-5602. 1989.[2] M.A. Baptista,., P.M.A., Miranda, J.M., Miranda,and L., Mendes Victor, Constrains on the sourceof the 1755 Lisbon Tsunami inferred fromnumerical modelling of historical data: J.Geodynamics, 25: 159-174. 1998.[3] E., Buforn, C. Sanz de Galdeano and A. UdiasSeismotectonics of the Ibero-Maghrebian region.Tectonophysics, 248: 247-261. (1995)[4] N.L. Grimison, and W.P., Chen, The Azores-Gibraltar Plate Boundary: Focal Mechanisms,Dephts of Earthquakes and their TectonicImplications. Journal of Geophysical Research,91, B2, 2029-2047. 1986.[5] E., Gràcia, J.J., Dañobeitia, and HITS cruiseparty,High-Resolution Imaging of TsunamigenicStructures in the SW Iberian Margin (Eurasia-Africa Convergence): Implications for SeismicHazard Assessment. EOS Trans AGU, 82(47),Fall meeting Suppl., San Francisco (USA),S51B-0610. 2001.[6] E., Gràcia, J.J., Dañobeitia, J., Vergés, andR., Bartolomé, Crustal architecture and tectonicevolution of the Gulf of Cadiz (SW IberianMargin) at the convergence of the Eurasian andAfrican plates. Tectonics, 22 (4), 1033-10572003a.[7] E., Gràcia, J.J., Dañobeitia, J., Vergés, andPARSIFAL Team, Mapping active faults offshorePortugal (36ºN-38ºN): Implications for seismichazard assessment in the SW Iberian Margin.Geology, 31(1): 83-86. 2003b.[8] R., Sartori, L. Torelli, N. Zitellini, D. Peis,and E. Lodolo, Eastern segment of the Azores-Gibraltar line (central-eastern Atlantic): Anoceanic plate boundary with di f fusecompressional deformation, Geology, 22:, 555-558. 1994.[9] L., Torelli, R., Sartori, and N., Zitellini, Thegiant chaotic body in the Atlantic ocean offGibraltar: new results from a deep seismicreflection survey. Marine and PetroleumGeology, 14: 125-138. 1997,[10] N., Zitellini, L., Mendes Victor, D., CórdobaJ.J.,, Dañobeitia, R., Nicolich G.,, Pellis, A.,Ribeiro, R., Sartori, L., Torelli, and BIGSETSTeam, Source of the 1755 Lisbon Earthquakeand Tsunami Investigated. EOS Trans. AGU,82: 285-290-291. 2001.Georeferenced Photo-Mosaicing of the SeafloorR. Garcia, X. Cufí, R. Prados, A. Elibol, J. Ferrer, M. Villanueva, T. NicoseviciComputer Vision and Robotics Group, University of Girona,Campus Montilivi, Edif. P-4, Girona, Spain, E-17003. Tel. +34 972 418881.E-mail: rafa@eia.udg.es.1. IntroductionOptical imaging provides to scientists high levelof detail of the ocean floor. Unfortunately, un-derwater imaging has to face the problems relatedto the special transmission properties of the lightin the aquatic medium, namely absorption andscattering [1]. These transmission properties ofthe medium cause blurring of image features andlimited visual range [2, 3], restricting the practicalcoverage of a single image to only a few squaremeters.Seafloor imagery is routinely acquired in near-bottom geophysical surveys with AUVs, ROVs orsubmersibles. Due to the large number of imagesand the lack of adequate tools to properly visualizethese data, they are often under-utilized. If imagesare systematically acquired and properly aligned,a composite image that combines the set of framestaken from the camera can be built. This compositeimage is known in the literature as photo-mosaic,and can be used as a visual map for underseaexploration and research [4]. Seafloor photo-mosaicing is an important tool to study thestructure and characteristics of the seafloor,providing a “panoramic” view of the interestarea. They also provide the basis to carry outtemporal studies of the floor, by comparingphoto-mosaics taken at different times.FOTOGEO is a research project funded by theSpanish Ministry of Science and Technologywith the aim of developing new algorithms andtechniques to build seafloor photo-mosaics.Specifically, the test bed of the project will beprocessing a large set of seafloor images col-lected over the Lucky Strike site during theLUSTRE’96 cruise [5]. This is one of thehydrothermal vent sites in the MOMAR areathat is the focus of integrated studies to charac-terize active processes and their interactionsat the axis of slow-spreading ridges. An ARGOII survey was carried out over the vent field(map), with N-S and E-W tracks spaced at ~50m, with closer spacing over particular vent fields.A total of 20.000 black and white, electronic stillimages where recorded. At the same time, navi-gation data of the vehicle Argo II was acquiredby means of an acoustic transponder network(LBL).

Active tectonic and sedimentary processes along the São Vicente Canyon (SW Iberian Margin): High-Resolution Imaging

Abstract

Similar works

Full text

Available Versions

Digital.CSIC