Importance of AE Study for Fracture Process of Heterogeneous Solid Material-High-Speed, Multi-channel AE Measurement System in Geological Survey of Japan/AIST

In order to investigate detailed features of the space-time distributions of microfractures generated during rock fracture experiments, we have developed a high-speed, multi-channel acoustic emission (AE) waveform measurement system. This system consists of 32 channels of transient-memory controlled by a microcomputer. The transient-memory has a 16 MB RAM buffer in each channel, which enables us to record the waveform data for more than 8000 AE events. AE waveform is digitized with a sampling interval of 50 nanoseconds and a resolution of 12 bits, and is recorded on the RAM buffer with a very short system dead-time of about 200 microseconds. We have also developed a visual and interactive processing system for dealing with a huge amount of AE waveform data. From AE waveform data, P-wave first arrival time is automatically picked, and AE hypocenter is determined. The AE data processing system also has functions of manual re-location of AE hypocenters, focal mechanism determination, some statistical analysis of AE time series, and so on. Using this system, we clearly found clustering of AE hypocenters around a macroscopic fracture plane during a 10 second interval before final fracture of a granite sample under triaxial compression. This demonstrates that the system could be a very powerful tool for studying the space-time distribution of AE events, especially when the AE activity is very high.