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Offset Vertical Seismic Profiling: Two-Dimensional Forward Modeling with Asymptotic Ray Theory
Michael H. Mellen
Submitted
to the Department of Earth, Atmospheric, and Planetary Sciences on May 11,
1984 in partial fulfillment of the requirements for the degree of Doctor of
Philosophy
Abstract
Offset vertical seismic profiling (VSP) is rapidly becoming a viable technique for delineating, in detail, subsurface geologic structure. In an effort to understand and use the information available in VSP data, a modeling study using asymptotic ray theory (ART) is undertaken. The basic theory and practical considerations for implementing ART in two-dimensional fully elastic media are discussed. A number of synthetic examples for simple models are presented to exhibit the effects of offset sources and laterally varying structures. Traveltime, amplitude, and phase effects are observed. The models show the significance of mode converted shear waves and the importance of full elastic modeling capabilities. Features in the data helpful in locating buried structures are investigated. A favorable compaison of ART synthetics to an actual VSP dataset acquired near a reef structure in northern Michigan is made. The agreement of both traveltime and amplitude effects shows the utility of the modeling technique in both field program planning and interpretive modeling.
