Experimental study of the fracturing process in brittle rock

Many small cracking events or microfractures precede fracture in laboratory compression tests on rock. Each event radiates elastic waves. During the compression of granite to fracture, twenty-two of the largest microfracture events were located in space by using first arrivals of S waves detected with a multitransducer array. At about 92% of the fracture stress, a rapid acceleration of microfracturing activity occurred. The location of the events that occurred below this point showed no obvious relation to the eventual fault. At stresses within the region of accelerated activity, however, there was a marked clustering of microfractures on the eventual fault plane. These observations suggest that the approximate time and place of fracture could have been predicted. In the light of the similarity of microfractures and earthquakes, this suggests a possible method for predicting earthquakes.