Seismogram (CPW), 112 km (70 mi) NW of Mount St. Helens, May 18, 1981
Detailed Description
Annotated seismogram indicates the signals for a Low-Frequency (LF) volcanic earthquake, relative quiescence, and then harmonic tremor as the eruption of May 18, 1980 accelerated. Each horizontal line represents 15 minutes of time.
Sources/Usage
Public Domain.
CPW seismic station