Abstract
Louie et al. (1988) apply to COCORP survey data a prestack migration process, which they describe, to image better reflections associated with structure in the upper 5 km of the San Andreas fault zone near Parkfield, California. They demonstrate the usefulness of this approach in an area along the survey where, as they point out, the CMP-stacking process may be particularly troublesome. While the authors were sensitive to the extreme lateral heterogeneities in and about the fault zone, the crooked survey line, and the complex terrain in which the survey was mounted (McBride and Brown, 1986), I suspect they were nevertheless a little too zealous in discounting, in this case, the value of conventional stacking applied and interpreted judiciously. Moreover, Louie et al. imply that their approach yields previously unobtained results; however, this is not the case.
The discovery of structural features within the deep crust across the United States by the COCORP consortium through the use of conventional stacking is a highly significant achievement. The data sets they recorded are a valuable national resource that can be analyzed in many ways to address diverse geologic problems. Conventional stacking of the data provided initial glimpses of the nature of the crust. Other types of analysis may, however, be required to explain particular aspects of the data and to resolve more difficult structural problems.
