Tsunamigenic-seismogenic structures, neotectonics, sedimentary processes and slope instability on the southwest Portuguese Margin

Terrinha, P., Pinheiro, L. M., Henriet, J.-P., Matias, L., Ivanov, M. K., Monteiro, J. H., Akhmetzhanov, A., Volkonskaya, A., Cunha, T., Shaskin, P. and Rovere, M. (2002) Tsunamigenic-seismogenic structures, neotectonics, sedimentary processes and slope instability on the southwest Portuguese Margin. Marine Geology, 195 (1-4), 235-258. (doi:10.1016/S0025-3227(02)00682-5).

Abstract

Tectonically active structures prone to cause devastating earthquakes and tsunamis, e.g. the Lisbon 1755 earthquake, were investigated during the UNESCO/IOC Training Through Research-10 (TTR-10) cruise on the southwest Portuguese Continental Margin using single channel seismic profiles, a 3.5-kHz hull-mounted sea-bottom profiler, 10-kHz OKEAN long range side-scan sonar, 30-kHz ORETECH deep-towed side-scan sonar, and a high-resolution deep-towed sea-bottom profiler. These data allowed the definition of new active faults and the establishment of morphological criteria for the classification of active faults in the study area. Landslides associated with the activity of a major tectonic structure, the Marquês de Pombal Fault, and other areas with clear signs of mass wasting phenomena were mapped. A slope-to-basin sedimentary system comprising 21 sedimentary ridges up to 20 km long was mapped and described. It was found that the sediments are mainly transported into the deep basins by mass transport processes across the steepest fault scarps forming a channel–levee system, while gravitational slides/slumps dominate the shallower slopes. The sedimentary ridges with an elevation of 40–50 m (50–60 ms TWT) above the seafloor are imaged on the high-resolution seismic profiles as an alternation of high and low amplitude reflectors. It is shown that the Pereira de Sousa Fault, its plateau and the Príncipes de Avis Plateau are experiencing uplift according to sedimentary and morphological criteria.

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