Sedimentology, physical properties and age of mass transport deposits associated with the Marques de Pombal Fault, Southwet Portuguese Margin

摘要

The SW Iberian Margin is located at the convergence of the European and African Plates, where the largest magnitude earthquakes in Western Europe occur. Several active structures, such as the Marques de Pombal fault, are potential sources of large magnitude earthquakes and tsunamis. Associated with faulting, submarine landslides are also commonly observed. A large area (similar to 260 km(2)) of high acoustic backscatter in the central part of the Marques de Pombal escarpment corresponds to a complex translational slide and debris flow. Detailed lithological description, physical properties and dating of four sediment cores sampled on the toe of the slide allow us to investigate the sediment facies, age and triggering mechanism of the Marques de Pombal slides. The maximum age of the Marques de Pombal landslide is 3270 +/- 60 Cal yr BR Radiocarbon dating of previous and subsequent Holocene mass wasting deposits gives an estimated recurrence rate of < 2 kyr. Although a number of mechanisms may be invoked to account for landslide triggering, earthquakes are the most likely triggering mechanism for the observed slope instabdities in the Marques de Pombal area, at least during the Holocene.