Study of Original Phases Stations Correction and Common Signal

Abstract : In a first approach, we have evaluated the attenuation due to geometrical spreading and anelasticity of recorded regional phases for a set of selected earthquakes which occurred in France or around the French territory. This purely experimental study leaded to the conclusion that a global attenuation factor in the range of distances from 100 to 1000km could be defined on broad band data (0.5 - 16Hz). In a second approach, we tried to model regional phases by using the Bouchon's method, in order to understand the influence of the source (depth, source mechanism) and of the propagation model on the seismograms built at various distances. The principal part of this report concerns the study of Lg phases in France. We show here that it is possible to derive directly from the records, not only the attenuation but simultaneously the source function and the transfer function at each station. We also present in this report, the first part of a signal processing, which will enable to improve the magnitude determination of quakes as well as the transfer function of our network for teleseisms. Keywords:Seismic waves; Attenuation; Data processing.