| Since 1980, analysis of seismic signals recorded by the University of Washington (UW) and the U.S. Geological Survey (USGS) Mount St. Helens seismic network have been analyzed and correlated with observations made by field crews, pilots, radar operators, and the general public. These analyses have led to the development of criteria that enable identification of most kinds of seismic events that occur at Mount St. Helens. These events include gas-and-ash explosions, volcanic earthquakes, volcanic tremor, rockfalls, debris flows, dome-building eruptions, and many types of man-made seismic noise. Identification criteria are based on comparison of signal envelope, dominant frequencies, and relative amplitudes and timing among stations. -- Jonientz-Trisler, et.al., 1994 |
