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.
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Kusunose et al. (1986) studied this question.
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