The south eastern durance fault permanent network: Preliminary results.

Volant, P; Berge-Thierry, C; Dervin, P; Cushing, M; Mohammadioun, G; Mathieu, F.
JOURNAL OF SEISMOLOGY, 4: (2) 175-189.

The Durance fault area is located in South Eastern France. This fault system is characterized by historical earthquakes (one every century, since 1509, with a magnitude between 5.0 and 5.3). This is the only fault in France with such a periodic historical seismic activity. In order to study an active fault in a moderate seismic context, the irsn (Institute for Nuclear Safety and Protection) decided to install a permanent network in 1992, surrounding the fault area. Such a permanent seismic network has been installed in the french Pyrenees in the Arette area (Gagnepain et al., 1980). While the Arette network covers a region affected by several major faults, our network is devoted to the study of the specific Durance fault. Major historical earthquakes are clearly associated with this structure. From an instrumental point of view, few earthquakes have been recorded since 1962 with the national network. Our network shows a small seismic activity, with the epicenters well aligned along the fault direction. Moreover, focal mechanisms computed for two events agree with the regional microstructural studies (Cushing et al., 1997). Finally, a study of the shear wave splitting underlines preferential S wave polarization for two stations. The H/V ratio on noise microtremors has been computed for each station in order to check their positions in term of site effects. It does not exhibit any amplification effect (except for two stations). The comparisons with H/V ratio on earthquake dataset show the important biases we can obtain with real earthquakes.