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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.


Public Domain.

CPW seismic station