State of the art

The Azores-Gibraltar Plate boundary (AGP) /Fig. 1 connects the Azores triple junction with the continental collision zone of the West-Mediterranean and separates the Eurasian Plate from the African plate. Along this line the relative motion is divergent West of the Azores, transcurrent in the middle part and convergent East of Tore Madeira ridge to the Gibraltar Strait. Here diffuse compressional deformation is present, as testified by scattered seismicity. Topography, geoid and gravity anomalies indicate significant deformation in a wide area, either in the oceanic or in the continental crust. Major seismic events, like 1755 Lisbon Earthquake PEREIRA1919 that may have reached extreme magnitude (M=8.5) require large rupture areas and perhaps large displacements. This suggests a transitional tectonic regime where new plate boundaries are being nucleated and significant deformation is occurring in a compressive setting (Ribeiro et al., 1996). Notwithstanding considerable efforts devoted during the last two decades in the understanding of the geodynamic regime at the continental margins of the Southwestem European block PURDY1975, MAUFFRET1989, PINHEIRO1992, WHITMARSH1993, SARTORI1994, BANDA1995, GONZALES1996 the deformational process present in the offshore of SW Portugal is practically still poorly understood.