A tornillo event is a low-frequency seismic event associated with volcanoes. The term, which means "screw" in
Spanish, was coined in the mid-1990s at the Observatorio Vulcanológico y Sismológico de Pasto (OVSP) in
Pasto,
Colombia
Colombia (, ; ), officially the Republic of Colombia, is a country in South America with insular regions in North America—near Nicaragua's Caribbean coast—as well as in the Pacific Ocean. The Colombian mainland is bordered by the Car ...
to describe seismic events seen at the
Galeras volcano.
A tornillo has the following characteristics that distinguish it from other seismic events:
* very limited distribution of
frequencies
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
(
monochromatic
A monochrome or monochromatic image, object or color scheme, palette is composed of one color (or lightness, values of one color). Images using only Tint, shade and tone, shades of grey are called grayscale (typically digital) or Black and wh ...
)
* a long
coda
Coda or CODA may refer to:
Arts, entertainment, and media Films
* Movie coda, a post-credits scene
* ''Coda'' (1987 film), an Australian horror film about a serial killer, made for television
*''Coda'', a 2017 American experimental film from Na ...
that decays slowly
* small
amplitude
Like
volcanic tremor, tornillos are thought to be caused by
magma moving at depth.
References
Tornillo-type seismic signals at Galeras volcano, Colombia, 1992−1993
External links
Observatorio Vulcanológico y Sismológico de Pasto - INGEOMINAS
Seismology
Volcanology