1. Combining the records from several sources at nearly the same location without correcting for static or offset differences. Used especially with surface sources in which the records from several successive weight drops, vibrations, pops, etc., are combined to give in effect the field record which would have resulted from a much stronger source. 2. Adding together the traces of a vertical seismic profile after time-shifting so as to horizontally align upward-traveling waves. 3. Sometimes used (incorrectly) to mean uphole stack (q.v.).