Xl. Lei et al., On the spatio-temporal distribution of acoustic emissions in two granitic rocks under triaxial compression: the role of pre-existing cracks, GEOPHYS R L, 27(13), 2000, pp. 1997-2000
We used a new rapid data acquisition system to examine the role of pre-exis
ting crack density in determining the mechanical properties of crystalline
rock. Two similar coarse-grained samples, Tsukuba granite (TG) and granitic
porphyry (GP), were used in triaxial compression tests. The main differenc
e between the: two rocks is that TC contains main large pre-existing cracks
, whereas GP is almost crack-free. In our tests, the two rocks showed signi
ficantly different behaviors. In GP, before the fault nucleation, AE activi
ty was low and showed increasing b-values with increasing stress. But in TG
, a large number of AEs were observed and showed short-term b-value anomali
es - mutual fluctuations on a decreasing background. The short-term fluctua
tions of b-values are closely correlated with those of the spatio-temporal
clustering of AE locations. Our results demonstrate: 1) pre-existing cracks
are the most dominant factor of all heterogeneities that govern the fault
nucleation process in laboratory rock samples; 2) failure predictability is
dependent on the pre-existing crack density.