Abstract
Seismic-wave velocities in cracked rocks increase with stress. It is believed that, within less than half the rupture pressure, this velocity increase occurs due to the closure of cracks. Previous studies have shown that, if a cracked rock is subjected to three mutually perpendicular stresses, the velocity increase is maximum in the direction parallel to the maidmum stress axis and minimum in the direction parallel to the minimum stress axis. Furthermore, some investigators have been able to relate the pattern of velocity increase with stress to the preferential crack directions (if any) and the type of stress-induced anisotropy. In this study P-and S-wave velocities were measured in a cubic sample of Westerly granite subjected to two perpendicular axial stresses (ranging from 0 to 7.0 MPa). The general agreement in the velocity values in different directions at zero pressure suggests an isotropic rock sample. The P-wave velocity increased by about 9% along the direction of the maximum stresses and about 3% along the direction of the minimum stresses and showed an anisotropy of about 6%. The shear-wave velocity increased by different amounts in different directions. The amount of increase ranged from 3.4% to about 6%. The anisotropy in S-wave velocity was in the order of 1.6%.
Al-Shaibani, Abdulaziz Muhareb (1994). Variation of seismic-wave velocities in westerly granite under stress. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1994 -THESIS -A4617.