The pyrenean earthquake of february 29, 1980: An example of complex faulting

An M_b = 5.1 earthquake occurred on February, 29, 1980, in the Western Pyrenees near Arudy (France). The telemetred network of the I.P.G.P., operating in this area since 1978, allowed a good localization of this earthquake (43°4.21′N, 0°24.59′W, depth 4km). During the two years preceding this earthquake the seismic activity exhibited a gradual decrease. A foreshock of magnitude 1.6 was recorded three hours before the main shock.A temporary network set up in the epicentral area a few days after the main shock permitted a precise study of the aftershock sequence. Fifty fault-plane solutions for earthquakes ranging from magnitude 1.5-4 were obtained. A complex pattern of faulting was revealed, with both strike-slip and normal faulting. However, a regional tectonic stress tensor can be proposed from a detailed investigation of the aftershock sequence. This stress tensor is in agreement with previous results in this area.