foreshock

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Related to foreshocks: Seismic waves, Aftershocks

foreshock

[′fȯr‚shäk]
(geophysics)
A tremor which precedes a larger earthquake or main shock.
References in periodicals archive ?
3 earthquake that turned out to be a foreshock of the massive magnitude 9.
Seismologists generally say that if there's a foreshock - a smaller shaker that precedes a quake - that measures at least 5.
Foreshocks are smaller earthquakes that follow the largest earthquake in a series of quakes, said Solidum.
In 1975, Chinese officials evacuated the city of Haicheng in part because of a series of foreshocks in the area, but also because of observations of typical pre-earthquake animal behavior.
The foreshocks had offered a warning signal, and this amazingly successful earthquake prediction probably saved tens of thousands of lives.
As for the estimate from seismologists that there is a 5 percent chance that the weekend aftershocks are actually foreshocks to a larger earthquake, Sheridan said she can't worry about it.
He also focuses on the unusual pattern of foreshocks and altershocks.
A pair of seismologists studying those foreshocks has found they exhibit an unusual characteristic that could help scientists predict some future earthquakes.
The same question applies to true foreshocks, which precede a larger quake by minutes, hours, or days.
Many big quakes involve foreshocks that precede the most serious shaking by days or minutes.