Investigations on Local Seismic Phases and Evaluation of Body Waves Magnitude (Western Europe)

Abstract : During 1986, most of our efforts have concerned a better understanding of seismic sources and propagation on local and regional sismograms and m sub b optimum determination. The influence of source depth on local seismograms (10 - 60 km) has been carried on by using synthetic seisograms. Pg and Sg waves amplitudes are less influenced than Rg waves amplitudes by depth variations. Rg waves amplitudes are clearly decreasing when depth increases. We need to apply such a discriminant on real cases. A tomography method is used on Q Lg determination from regional seismic data over France. A systematic Q computation on a large amount of data is necessary to have a reasonable statistical value. For that purpose, a regional seismic data base including digital records and corresponding sources obtained by inversion technique (with a mean geometrical and anelastic attenuations) is prepared. More than 400 earthquakes are processed, all of them located in France or vicinity at crustal depths. Studies and processing concerning a better m sub b evaluation on teleseisms recorded on a large network (L. D. G. network) are continuing. Keywords: Quality factor; Source function; Data processing; Seismic moment; Stress drop; Fault dimension; Western Europe.