To investigate detailed features of the space-time distributions of microfractures generated during rock fracture experiments, we have developed a new high-speed, multi-channel acoustic emission (AE) waveform recording system. The system consists of 32 channels of transient-memory controlled by a microcomputer. The transient-memory has a 16MB RAM buffer in each channel. The large amount of RAM buffer enables us to record more than 8000 AB events with very short system dead-time, which is the time interval in which we are unable to detect an AE event due to recording of waveform data. The dead-time is about 200us before the RAM buffer becomes full, and about 0.4 5 afterwards. The newly-introduced controller, which can check the status of the RAM buffer, synchronizes the transient-memory so that all channels can record an AE event at the same time even after the RAM has been filled. 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 new system could be a very powerful tool for studying the space-time distribution of AE events, especially when the AE activity is very high.
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