Earthquake seismic Gaussian beam depth migration

Although the earthquake seismic recording is extremely sparse, there is in fact no lack of information available for migration. When an earthquake occurs, thousands of seismic stations all over the world record the signal. The signal is scattered, diffracted, and reflected throughout the neighborhood of the source. The source position can be located by direct wave traveltime inversion (Aki and Richards, 1980; Stein, 1991). The low wavenumber smooth background velocity model of the earth is assumed to be known. The scattered signal received at the numerous seismic stations is backprojected as Gaussian beams to the neighborhood of the source and the profile migration imaging condition is applied. The migrated image can then been made visible through constructive interference of adjacent wavelets, since we have numerous seismic stations deployed on the earth surface. The result is the high wavenumber velocity band, the reflectivity image of the neighborhood of the source. The records of each earthquake source are then migrated separately to obtain the local images near the sources. Finally, the local images from the many earthquakes are concatenated to form the global reflectivity image.