Near-offset vertical seismic profiling (VSP) is an established technique to obtain interval velocities for lithology characterization, time-to-depth calibrations, and seismic data processing. Unfortunately, these velocities are often insufficient to distinguish lithology types and can disagree with surface seismic stacking velocities. Multiple-source offset VSPs provide additional travel time information for calculating interval anisotropic velocities that can help discriminate lithology. In this paper, a technique is developed for computing transversely isotropic phase velocities over intervals less than the dominant seismic wavelength. Independent estimates of vertical and horizontal slowness are made for each receiver depth and source offset pair. These provide the magnitude and direction of phase velocity for calculating the in situ elastic properties of a transversely isotropic medium. This technique requires the assumption of lateral homogeneity because horiozontal slowness components are related to surface properties between sources and not to rock properties between receivers at depth.

Factors that violate this assumption such as source elevation differences and dipping layers are evaluated with synthetic data. Six impulsive source P wave offset VSPs in a 663-m well in east Texas are analyzed and a near offset SH wave vibrator VSP provides vertical shear wave phase velocities. Strong transversely isotropic velocity variations observed in the Tertiary and Cretaceous sediments penetrated by this well correlate with lithology types, suggesting that this technique is sensitive to local properties at the receiver. These results may not indicate exact intrinsic elastic properties and could be due in part to dipping layers, vertical heterogeneities, and unknown local surface variations. Percent ''phases velocity'' anisotropy appears to increase from 6 to 20% for P wave and 10 to 50% for SV wave with increasing amounts of calcareous material and shale in the rock. (Percentage anisotropy is defined as the ratio of the horizontal to vertical velocity for P waves and the ratio of velocity at 45¿ to vertical velocity for SV waves.) Sandstones and chalk exhibit the least amount of anisotropy, while the shales and calcareous shale exhibit the most. ¿American Geophysical Union 1990