No abstract

Comparisons of longitudinal (compressional) wave velocity with structural subfabrics have been made for Yule marble, Newberry Crater pumice, and Salisbury granite. Velocities were (1) measured omnidirectionally in spherical specimens by an ultrasonic pulse technique and (2) plotted and contoured on equal area nets. These contour patterns show velocity anisotropy that can be interpreted in terms of elastic symmetry. Microstructural subfabrics were determined from oriented thin sections of the specimens. Subfabrics were then displayed on equal area nets for comparison of their symmetries with those of the longitudinal wave velocities. The two structural subfabric elements selected for comparison were crystallographic orientation of constituent anisotropic minerals and shape and orientation of pores or cracks. The longitudinal velocity symmetry in Yule marble appears to be axial, whereas in both Newberry Crater pumice and Salisbury granite the pattern is orthorhombic. The pattern of longitudinal velocity anisotropy is associated with preferred orientation of calcite optic axes in Yule marble, preferred orientation of elongate vesicles in the Newberry Crater pumice, and preferred orientation of microfractures in quartz in the Salisbury granite. A prospectus given suggests that the petrophysical technique described can be used to determine elastic symmetry, orient rock to inherent elastic symmetry axes, indicate sample homogeneity, and supplement conventional petrofabric techniques.

Many applications of ultrasonic pulse techniques for studying the elastic behavior of rock have already been disclosed by Hughes et al (1950, 1951, 1952, 1957), Birch (1960, 1961), Simmons (1964 a, b, 1965), Christensen (1965, 1966a & b), and others. Although similar ultrasonic pulse measurement systems have been described by Tocher (1957), Fairhurst (1961), and Gregory (1967), the system described in this paper is automatic and permits continuous monitoring of elastic wave traveltime. Once set up, the system can record elastic wave traveltime at a preset rate for nearly any time period without intervention by an operator. This automated system has been used to study effects of environment on longitudinal pulse velocity in several rocks (Podnieks et al, 1968) and to make other preliminary investigations of longitudinal pulse velocity variations in rock under external influences. This report notes also several applications to problems of current interest to investigators of the elastic properties of rock.

No abstract

No abstract