Spatial distribution of earthquakes in the SW iberian margin has been studied for the period 1984-1994. in the basement of the continental margin of iberia active fault zones occur, showing different trends: NW-SE, NE-SW and E-W. Seismicity is focused in a major limit between two continental blocks. It is concluded that this limit is an active fracture zone, extending from the Huelva meridian at least to the San Vicente cape. Crust in the SW Iberian margin is estimated to be about 30-35 km thick, whereas a thickness of 60 km is suggested for the whole lithosphere