REGIONAL CODA Q-VARIATIONS IN THE WESTERN ALPS (NORTHERN ITALY)

To study the microseismicity of the central segment of the western Alps, a local temporal seismic network of six stations was installed in addition to the regional centralized network operating in the area. In 3 months about 220 shocks, with magnitude ranging between 1.0 and 3.8, have been analyzed and located. The epicenter distribution shows a possible subdivision into seismogenetic bands. This subdivision is also recognizable from the spectral characteristics of the analyzed seismic signals. A study of the wave attenuation, in a restricted area well covered by the local network, was carried out through a 'coda' analysis. The results show strong spatial Q(c) variations, in agreement with the strong lateral heterogeneities that characterize this area. In particular, the Brianconnais domain, the crystalline massifs and the inner part of the Alpine are appear to behave as decreasing attenuation bands.