Although several real-time detection and recorder systems exist, few address the problem of continuously measuring the amplitude of seismic signals during volcano-crisis conditions, when individual events are difficult to recognize. We developed a real-time seismic-amplitude measurement system (RSAM) that uses an inexpensive eight-bit analog-to-digital converter controlled by a laptop computer to provide 1-minute-averaged, absolute-amplitude information for eight seismic stations near Mount St. Helens. The absolute voltage level for each station is digitized at 50 samples/second, averaged, and immediately transmitted to a host computer for analysis. The RSAM proveds a convenient-to-access, continuous time history of seismic activity at the volcano. RSAM systems calculating 10-minute amplitude averages have been installed at the Cascades, Alaska, and Hawaiian Volcanoes Observatories. The RSAM has been a useful tool in predicting eruptive activity at Mount St. Helens and Redoubt Volcano, Alaska.
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