Effect of dilatancy on velocity anisotropy in Westerly granite

Journal Article · Sun Sep 10 04:00:00 EDT 1978 · J. Geophys. Res.; (United States)

OSTI ID:6050341

Martin, III, R J; Mizutani, H; Soga, N; Spetzler, H

Jacketed samples of Westerly granite were fractured at confining pressures up to 1 kbar and at strain rates of 2 x 10/sup -5/ sec/sup -1/ and 3 x 10/sup -7/ sec/sup -1/. Compr and horizontally as well as vertically polarized shear velocities were measured in orthogonal directions perpendicular to the compression axis. At approximately 60% of the ultimate axial strain the onset of dilatancy is noted by a decrease in the vs and vp velocities. As failure was approached, the compressional velocity across the fault decreased by nearly 40% for the low-strain-rate case vs. about 225 for the high-strain-rate case. In order to characterize the stress-induced cracks during dilatancy, an analysis of the velocity data was conducted with the assumptions that flat spheroidal cracks were oriented perpendicular to 3 orthogonal directions and that the effects of oblique cracks were vectorially divided between the effects of 3 mutually perpendicular crack types. The comparison between the observed velocities and those calculated from the 3 crack densities on the basis of the above assumptions showed good agreement. 28 references.

• OSTI ID: 6050341
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 83:B9; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
ANISOTROPY
CRACK PROPAGATION
DILATANCY
FRACTURE PROPERTIES
GRANITES
IGNEOUS ROCKS
MECHANICAL PROPERTIES
PLUTONIC ROCKS
ROCKS
SHEAR PROPERTIES
STRAIN RATE
VELOCITY