IN SITU SEISMIC MEASUREMENTS OF CRACK ANISOTROPY IN THE CARBONIFEROUS LIMESTONE OF NORTHWEST ENGLAND*

Abstract

A bstract Seismic velocity anisotropy is predicted for cracked rocks containing either a naturally‐occurring or an artificially‐induced preferred orientation of cracks. Methods developed for the study of velocity anisotropy in the uppermost mantle have been applied to the in situ measurement of P‐wave velocity anisotropy in fractured Carboniferous Limestone in Northwest England. At three different sites, first‐arrival travel‐time data has been obtained using conventional refraction equipment and a weight‐drop source. Velocity anisotropy of 15–29% is identified with directions of maximum and minimum velocities that can be broadly related to previously mapped orientations of joints.