To better understand the phenomena leading to the failure of rock, unc
onfined compression experiments on Charcoal granite specimens were per
formed with the monitoring of acoustic emission (AE). Localization in
the form of spalling near the free surface was detected by the concent
ration of hypocenters. The AE locations, which look random in space an
d time before localization, actually were clustered and have fractal s
tructure in either space or time. After localization, the fractal dime
nsions reduced significantly in a certain range of distance and time.
The analysis of interaction between spatial and temporal clustering re
vealed the size of clusters in both space and time. The cluster sizes
may be related to the intrinsic properties of the rock. The seismic mo
ment tenser was evaluated through a deconvolution technique to obtain
the source mechanism and orientation of each AE event. The dominant mo
de of failure from AE was sliding on inclined planes, although a signi
ficant number of source planes were parallel to the loading axis, whil
e the growth of cracks perpendicular to the loading axis was inhibited
. This preferential growth of microcracks is related to a tensorial me
asure of damage and is used to study stress-induced anisotropy.