弹性波叠前有限元反时偏移

PRE-STACK FINITE ELEMENT REVERSE-TIME MIGRATION FOR ELASTIC WAVES

Based on the concept of reverse-time extrapolation, we have developed the pre-stack reverse-time migration method for elastic waves by means of the finite element method and applied it to migrate offset synthetic surface data last year. In this paper we apply the method to migrate both the synthetic surface data and the synthetic VSP (vertical seismic profile) data simultaneously. The migration results are improved by using both the surface data and VSP data: the migration images are accurately converged to the true depth of the reflec-tors.Another improvement in the migrated depth section is made by introducing "modified field" display technique, which combines the vertical and the horizontal component migrated sections. The noise in the previously migrated section, which blurs the migration images in each individual displacement component, is now well eliminated in the " modified field" migrated, depth section. Consequently, the migration images delineate the reflectors more clearly.Two synthetic examples, one with two elastic layers over an elastic half-space and the other with a composite elastic dipping and horizontal layer over an elastic half-space, are presented to show the improvement by using both the surface data and VSP data and by introducing " modified field " display technique.