Prestack depth migration of dense wide-angle seismic data

Prestack depth migration of wide-angle seismic data represents an extension of traditional imaging with near-vertical incidence data because it includes a larger component of the recorded wave field. To date, however, studies that have employed wide-angle migration have suffered because only widely spaced data were available and because only very simple synthetic tests were performed. Although wide-angle migration has the potential to increase our ability to image deep-crustal structures, particularly when closely spaced data are collected, a thorough study of this technique has been lacking. To address this, we present a case study of prestack depth migration of relatively dense synthetic wide-angle marine data. The objectives are to identify potential benefits and limitations of this approach and answer such fundamental questions as how close the receiver spacing must be for a typical survey to image effectively with wide-angle data. This will facilitate the design of better seismic experiments. Our study employs Kirchhoff prestack depth migration of variably spaced full wave-field synthetic wide-angle ocean-bottom hydrophone (OBH) data generated using a realistic velocity model based on the passive eastern margin of the United States. We show how an increase in OBH density improves the migration by increasing the lateral resolution and signal-to-noise ratio. We also investigate the contribution of various offset ranges to the migrated image and show how the wider-angle components contribute primarily to the deepest parts of the image with relatively low spatial frequency compared to the near-vertical incidence components. To investigate how errors in the velocity model affect imaging as a function of offset range we migrate the data using a velocity model derived from refraction and reflection traveltime inversion. This example demonstrates the need to obtain an increasingly accurate model as increasingly wider-angle data are migrated. To effectively image structures in our 200 x 40 hn synthetic velocity model, an OBH spacing of approximately 2 km is required. (C) 1998 Elsevier Science B.V. All rights reserved.