SIMULTANEOUS INVERSION OF REFLECTION AND REFRACTION SEISMIC DATA AND APPLICATION TO FIELD DATA FROM THE NORTHERN RIO-GRANDE RIFT

An inversion scheme that determines a velocity model simultaneously fr om normal-incidence reflection and refraction/wide-angle reflection se ismic data has been developed, tested, and applied to real seismic dat a. Simultaneous inversion minimizes the non-uniqueness of inversion re sults. A common midpoint (CMP) stacked reflection section provides a d etailed image of the structural configuration in time. Refraction or w ide-angle reflection data can be used to derive a velocity model. If b oth refraction data and normal-incidence reflection data are available along coincident profiles, simultaneous inversion of the data sets ca n produce an improved model. With the extra control of the interface d epth provided by reflection data, it is also possible to avoid ambigui ty of phase identification. The commonly used damped-least-squares (DL S) inversion method often results in significant inversion artefacts. We provide effective methods for reducing inversion artefacts using bo th damping and smoothing. From tests using synthetic data, we conclude that the simultaneous inversion scheme can improve resolution and can be applied to velocity models with a reasonably complex structure. Th e simultaneous inversion scheme has been successfully applied to coinc ident seismic reflection and refraction data recorded by the SAGE prog ram in 1990-1991 in the western boundary area of the Rio Grande rift n ear Abiquiu, New Mexico. In this example, the simultaneous inversion d erived a velocity model in which stratigraphic units and extensional f ault blocks can be resolved.