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Seismograph recording of harmonic tremor.
Four major types of seismograms, or seismic signatures.

A harmonic tremor is a sustained release of seismic and infrasonic energy typically associated with the underground movement of magma, the venting of volcanic gases from magma, or both. It is a long-duration release of seismic energy, with distinct spectral 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. 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 earthquakes and explosions.

The relation between long-period events and an imminent eruption was first observed by Bernard Chouet, a volcanologist who was working at the United States Geological Survey.[1][2][3]


  1. ^ Chouet, Bernard A. (1996). "Long-period volcano seismicity: its source and use in eruption forecasting". Nature. 380 (6572): 309–316. Bibcode:1996Natur.380..309C. doi:10.1038/380309a0. ISSN 0028-0836.
  2. ^ Interview with Bernard Chouet regarding his research into long-period events and volcanic eruptions: .
  3. ^ U.S. TV program on use of long-period events to predict volcanic eruptions: "Nova: Volcano's Deadly Warning": . See also "Volcano Hell" episode of BBC TV series "Horizon" on same subject: .

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