Harmonic tremor

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.

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

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]

Notes
  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: http://www.esi-topics.com/volcanoes/interviews/BernardChouet.html Archived 2009-02-01 at the Wayback Machine .
  3. U.S. TV program on use of long-period events to predict volcanic eruptions: "Nova: Volcano's Deadly Warning": https://www.pbs.org/wgbh/nova/volcano/ . See also "Volcano Hell" episode of BBC TV series "Horizon" on same subject: http://www.bbc.co.uk/science/horizon/2001/volcanohell.shtml .
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