Harmonic tremor describes a long-duration release of seismic energy, with distinct spectral (harmonic) lines, that often precedes or accompanies a volcanic eruption. More generally, a volcanic tremor is a sustained signal that may or may not possess these harmonic spectral features.
A harmonic tremor is a sustained release of seismic and/or infrasonic energy typically associated with the underground movement of magma and/or venting of volcanic gases from magma. Being a long-duration continuous signal from a temporally extended source, a volcanic tremor contrasts distinctly with transient sources of seismic radiation, such as tremors that are typically associated with earthquake and explosion.
For more info, see the work of Bernard Chouet, a USGS volcanologist who was working at the United States Geological Survey and who first observed a relation between long-period events and an imminent eruption.
Famous quotes containing the word harmonic:
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—Kyle D. Pruett (20th century)