AMPLITUDE SPECTRA OF ACOUSTIC EMISSION ARISING FROM STEPWISE LOADING OF ROCKS

Abstract

The method of acoustic emission (AE) was used to study defect generation during stepwise loading of granite specimens. The AE amplitude spectrum was found to shift to the left toward smaller values when the specimen was kept under a constant load after its rapid growth. It is hypothesized that the amplitude of acoustic pulses is proportional to the length of the resulting structural defect. The observed effect can be explained by overstresses being released at structural heterogeneities that had been caused by the stress growth. These results provide the indirect evidence of the hypothesis stating that the precursory period of an earthquake can be very short when the earth is under rapidly varying stresses compared with the estimates based on the traditional concept of a quasistationary stress distribution in the Earth's crust.