Changes in the numerical frequency of microearthquakes have been observed at various active volcanoes. Identification of these periods of change can be made with a short-period, vertical seismometer driving a simple tally register counting circuit. A fully portable prototype model tested at various active volcanoes provided rapid estimations of the occurrence of microearthquakes. On Kilauea Volcano, Hawaii, the numerical results correlate very well with counts made from conventional seismograms. The device is no substitute for continuous seismic records, but provides a very simple method of monitoring changes in local seismicity which can then be evaluated by more sophisticated equipment.
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