The coasts of Portugal, Spain and Morocco are earthquake and tsunami prone area as testified by the historical occurrence of large events, among which the "1755 Lisbon Earthquake" was one of largest episode ever occurred in this area. Part of the tectonic structure which probably cause this event has been recently identified offshore Cabo de Sao Vicente ZITELLINI1999. This identification is also reinforced by a recent backward ray-tracing tsunami modeling BAPTISTA1997, showing that the preferred solution implies a double rupture, trending NNW-SSE to NW-SE, centered approximately at 100 km W of Cabo de Sao Vicente, within the area encompassed by the present survey. BIGSETS 98 cruise was planned in order to investigate the tectonic and sedimentary history of the sedimentary column, the deformation pattem of the area surrounding the structure and of the thrust itself A MCS survey together with a SBP survey and core sampling were performed. In particular the SBP survey was planned to locate the faults, previously imaged by MCS survey, cutting the sediments till the sea bottom. The target of sampling were the erosional areas wherein the eventually collected pre-compressional sediments would allow the estimate of the uplift rate over both recent and long time spans. Once the geometry and kinematics of a seismo-tsunamigenic structure is defined, it is possible to estimate the characteristic earthquake associated with the rupture in one or more of its segments; the knowledge of the geometry of the source area, the knowledge of its present day activity and of the slip rate of the active structure, that may be inferred from vertical separation and from the age of the displaced sediments, is part of the information required to work out this estimate. Moreover the detailed characterization of the seismo-tsunamigenic source allows a better risk assessment and the definition of specific tsunami warning criteria.