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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.
Next: DISCUSSION
Up: PRESTACK GAUSSIAN BEAM DEPTH
Previous: Surface and crosswell seismic
Stanford Exploration Project
11/17/1997