Triggered telerecording seismic equipment*

Abstract

Electronic equipment is described which has been designed for research into the Witwatersrand earth tremors. It enables six seismograms (originating at different sites up to 17 km. away) to be recorded side by side on a common time scale. High-speed recording is obtained by automatically triggering the (usually stationary) recorder, while the signals are “stored” for six seconds on a magnetic tape delay unit so that no part of the record is missed. Automatic magnification control is used at the transmitting end, and a method of frequency-modulating a subcarrier, appropriate for transmitting very low-frequency signals, is described. Some seismograms obtained by this means are shown.