A portable seismic system designed for use in crustal experiments is discussed in this paper. The main features of the system which make it attractive are (1) a 7-lb commercial stereo tape recorder, (2) a simple chronometer, (3) a capability to be monitored in the field with a speaker rather than with a paper recorder, (4) a timer for self-operation, and (5) low overall power requirements.
The seismic signal from the seismometer is amplified and fed to one channel of the recorder via a voltage-to-frequency converter so that very low-frequency signals can be recorded. Three additional signals made up of a WWVB radio time signal, a 100-Hz oscillator signal (to be used for compensation) and a 10-sec mark from a chronometer are fed into the second channel of the stereo recorder. The total weight of the instrumentation including the seismometer and carrying case is only 51 lb. This system will operate for over 120 hr with 27 lb of 6-volt batteries. This is more than sufficient for most crustal experiments. Because of its lightness and self-operating features, the system can easily be transported to remote areas by light aircraft at a minimum of expense and trouble.