ANALYSES OF WAVE-FIELDS BY THE COMMON EXCITATION ARRAY (CEA) METHOD

There is a number of problems associated with the processing of seismi c data acquired over crystalline rocks where velocities vary as much i n the horizontal direction as in the vertical direction and near-surfa ce low-velocity layers may distort the signals recorded on the surface . In addition, waves arriving at the same time but at different dips w ill interfere with one another thereby masking reflections of interest . Traditional CDP processing has some difficulties associated with it in separating out the interfering events, as well as in imaging steepl y dipping events. By employing a series of closely spaced shotpoints i n an array, quasi-planar waves emanating at different angles may be si mulated through slant stacking. Slant stacking is preferably done in t he common receiver domain where statics and trace to trace signal vari ations are less of a problem since near-surface velocity variations ar e less of a problem. After slant stacking to illuminate interfaces of various dips, the major reflecting events may be picked automatically and the data quantity reduced to the time, slowness and amplitude of t he picked events. These picked events can then be migrated onto a dept h section image where the interfering waves have been separated from o ne another and steeply dipping events are imaged. We apply the method to seismic data from the Urals near the SG4 deep borehole and compare the results with CDP processing of the same data. Results show that th e common excitation array method matches the geological interpretation s in the area better and that it images steeply dipping reflectors bet ter.