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 in volcanoes, and with repetitive stick-slip or other impulsive activity in non-volcanic systems. It is a long-duration release of seismic energy, often containing distinct spectral lines. Volcanic tremor often precedes or accompanies a volcanic eruption. Being a long-duration continuous signal from a temporally extended source tremor contrasts distinctly with transient and often impulsive sources of seismic radiation typically associated with earthquakes and explosions.
Nonvolcanic, episodic tremor at plate boundaries (particularly in subduction zones) has been attributed to swarms of long-period earthquakes [1] and is distinguished by the term episodic tremor and slip (ETS) and may occur during slow earthquakes.
Iceberg impacts with the seafloor or other icebergs can also generate distinct iceberg harmonic tremor signals that propagate to large distances as ocean acoustic and solid Earth seismic wavefields. The source process of iceberg harmonic tremor has been attributed to highly repetitive quasi-periodic stick-slip at ice-seafloor or ice-ice contacts.[2]
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.[3][4][5]
See also
editNotes
edit- ^ Obara, Kazushige (2002). "Nonvolcanic Deep Tremor Associated with Subduction in Southwest Japan". Science. 296 (5573): 1679–1681. Bibcode:2002Sci...296.1679O. doi:10.1126/science.1070378. PMID 12040191. S2CID 32354691.
- ^ MacAyeal, D.R.; Okal, E.A.; Aster, R.C.; Bassis, J. (2008). "Seismic and hydroacoustic tremor generated by colliding icebergs". Geop. Res. Lett. 113 (F3). doi:10.1029/2008jf001005.
- ^ 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. S2CID 4341826.
- ^ 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 .
- ^ 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 .
External links
edit- Seismicity, low frequency events and tremor at the Katla subglacial volcano, Iceland
- The harmonic tremors of a volcanic eruption Archived 2012-03-16 at the Wayback Machine
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