Seismic triggering in a stable continental area: The Lugo 1995-1997 seismic sequences (NW Spain)

The northwestern area of the Iberian Peninsula traditionally is considered a seismically stable area. However, since 1979 this region has experienced a significant increase in seismic activity. In 1995 and 1997, two earthquakes, with magnitude Mw 4.2 and 5.1, respectively, caused significant damage in the region (intensity EMS: V). In this work, we analysed the focal mechanisms that had the most coherence with the local structures and tectonics. Modelling of the coseismic Coulomb static stress changes generated by the 1995 sequence was performed in order to find a possible genetic relationship with the 1997 sequence. Models using oblique (reverse strike-slip) movement on a fault with the same geometry and orientation as the Baralla fault, mapped at the surface, yield the best fit with the spatial distribution of the 1997 sequence. The existence of causal relationships between two close seismic sequences is important for the improvement of future seismic hazard assessments methodologies.