Acoustic imaging of thermally fractured rock

Recent proposals for the disposal of nuclear waste in granitic rock have generated interest in thermally induced fracturing of the rock formations. For these reasons, a program of research has been undertaken in the laboratory to image thermal fracturing using concurrent ultrasonic tomographic imaging and acoustic emission (AE) location. In these experiments, a cartridge heater was used to cycle the temperature of a 15-cm cubic rock sample in a series of heating phases. Full waveform AEs were acquired from a fixed array of twelve transducers during the heating cycles, while tomographic data were taken before and after heating, using four scanned transducers. Source locations and tomographic images correlated extremely well, both detecting the formation of macroscopic fracture patterns