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A system comprising digital telemetry remote stations and an on-line event detection and data recording station has been developed. The remote stations employ time-division multiplexing of up to three seismic sensors operating at sampling rates of 60 samples/s. Higher sampling rates are available if fewer sensors are used per station. The highest single-sensor sampling rate is 240 samples/s. Companding Â¿-255 law analog-to-digital conversion is performed on-site utilizing an eight-bit transmission format and exhibiting a 72-dB dynamic range. Event detection at a data collection station has been implemented on a microprocessor, which also handles data acquisition and synchronization with a standard-time clock. A slave microprocessor controls data transmission via telephone lines and data recording on magnetic tapes employing a standard format to permit off-line data analysis on a computer. Three digital-to-analog output channels are provided for on-line signal monitoring.