Abstract
Three-dimensional (3-D) locations of acoustic emissions (AE) and P-wave velocity anisotropy were investigated to analyse the failure zone development in two Yugawara andesites. The results were obtained during the deformation of rock under incremental loading and short-duration creep regimes at a confining pressure of 40 MPa. Creep tests were carried out at a constant differential stress of about 90–95% of short-term fracture strength of andesites for the single- and two-stage creep experiments. In both the experiments, the AE activity during loading was mostly confined to two region where AE hypocentres concentrated near the cylindrical surface of the rock. Prior to fault nucleation, the localized zone of microcracks attained a spheroidal shape in one sample and planar shape in the other. P-wave velocity anisotropy increased to 44% as final failure approached in the rock. The loading rate and the magnitude of creep stress were found to have a profound influence on the details of failure zone development and times of failure of the rocks studied.
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