Actividad sísmica en el Noroeste de la Península Ibérica observada por la red sísmica local del Proyecto Gaspi (1999-2002)

The northwestern part of the Iberian Peninsula is of low to moderate magnitude within the seismotectonic context of the Euro-Mediterranean region. However, a significant increase of the seismic activity has taken place since 1995. Several crises occurred in Lugo province, with a main earthquake of magnitude 5,3 in 1997. The poor coverage from permanent stations monitoring the area has traditionally made difficult any rigorous analysis of this activity. Hence, we undertook a detailed study of the local seismicity between 1999 and 2002, based on the deployment of a temporary seismic array. More than 500 local events were collected during this period. The seismicity is scattered over the NW Iberian Peninsula including the continental platform. The highest concentration of events is located in the Southern and Eastern part of Galicia, decreasing progressively towards the western part of Asturias. The most active seismic focus is located near the epicentre of the 1997 earthquake (SW of Becerrea, Lugo). The detection of a poorly-known ‘background seismicity’ through all the NW Iberian Peninsula is another important finding of this work. The results allow to differentiate two seismotectonic domains within NW Iberia: the Atlantic and the Cantabrian domains. In the Atlantic one the seismicity seems to be associated mainly to a NNE-SSW fault system. Lower activity has been found in the Cantabrian domain were the active faults are generally NNW-SSE oriented. The most active zone coincides with the limit between these two zones.