AE GAP PRIOR TO LOCAL FRACTURE OF ROCK UNDER UNIAXIAL COMPRESSION

Abstract

Acoustic emission (AE) was monitored during uniaxial compression of andesite and granite specimens, and their hypocenters were located with an accuracy of a few millimeters in a cylindrical sample of 10 cm in length and 5 cm in diameter. P-wave polarity data suggests that AE is radiated from a shear-type cracking. We expect that the stress field is monitored by the mechanism solutions. An AE gap that is very similar to a seismic gap of the second kind defined by Mogi in 1979, was observed prior to an extremely large AE in an andesite specimen under uniaxial compression of about 90% of the fracture strength. The focal mechanism solutions for the foreshocks and aftershocks of the large AE suggest that the local stress field changes by the main shock.