PRECURSORY LOCALIZATION AND DEVELOPMENT OF MICROFRACTURES ALONG THE ULTIMATE FRACTURE PLANE IN AMPHIBOLITE UNDER TRIAXIAL CREEP

In a triaxial creep experiment in amphibolite, we clearly found a prec ursory localization and development of microfractures along the final fracture plane using an AE (acoustic emission) source location techniq ue. The precursory localization of AE hypocenters first nucleated near a pre-existing macroscopic defect and then extended gradually along t he final fracture plane prior to failure. On the other hand, no signif icant precursory localization of AE hypocenters on the final fracture plane before failure has been reported in rock samples free of pre-exi sting macroscopic defects. This difference in AE occurrence patterns b efore failure could be explained by the difference in the degree of da mage in the portion of the rock surrounding the localization zone when it nucleates.