A portable digital recorder with event-triggering capability has been designed, and four have been constructed and field tested. The design was based on that used for over 2 years in ocean bottom seismic capsules. The outputs of as many as four seismometers are amplified, filtered, and digitized continuously at 64, 128, 256, or 512 total samples per second. The digital data are mixed with a time code, identification and synchronization patterns, serialized, and passed through a 512, 1024, or 1536 sample shift register which acts as a delay line. Data are then recorded on an unmodified Sony TC800B tape recorder which is turned on when a seismic event occurs. The event is triggered when the analog/digital converter output jumps above a preset threshold. Data are recovered using the same or a similar recorder for playback. A decoder provides an analog output for field interpretation or a digital output for computer compatible input. The tape recorder capacity is 1.4 million samples, or 3 hr of recording of a single channel at 128 samples per second.

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