f Determination of transverse isotropy parameters from multiple offset VSP data

The Imperial College borehole test site in Northumberland, England consists of four 250 metre vertical holes which intersect a horizontally layered cyclical sequence of sandstones, shales and carbonates of the Namurian Upper Limestone Group. Our long term objective is to study seismic attributes (anisotropic velocity, attenuation, dispersion, reflectivity) over a very wide frequency range (50 Hz to 500 KHz). Previous studies at the site (Sams et al, 1993) have established that differences in horizontal to vertical P wave velocities of up to 25% determined from core samples are consistent with transversely isotropic velocities deduced from crosshole data which have a dominant frequency of approximately 1 kHz. The aim of this experiment is to determine elastic parameters at the low end of our frequency range.