foreshock

IPA: fɔrʃɑk

(geology) A small earth tremor which precedes the mainshock in an earthquake sequence. Not all mainshocks have foreshocks.
Any shock or disturbance that precedes an event

Examples of "foreshock" in Sentences

The post-Lehman banking crisis could yet prove to have been just the foreshock.
A foreshock to Thursday's earthquake occurred in April 2009, when the stock of Dendreon
There was a major tremor, magnitude 7.9, just two days ago - what now looks like a foreshock.
When we get a swarm like the one in Berkeley, it doesn't come with a tag that says it is a foreshock.
It would be bigger than the original quake, then the original quake would be a foreshock rather than the aftershock.
If the team's results are correct, then this swarm is probably not a foreshock of something larger on the Hayward Fault.
It has been longer than that, so now we believe the 7.0 was the major quake and not a foreshock, thanks goodness, to a larger quake.
Smaller aftershocks often accompany a large quake, and scientists say there is a small—and decreasing—chance that Tuesday's quake could actually be the foreshock to a bigger quake.
Occasionally there will be foreshocks, but unfortunately, we never really know when a smaller earthquake is a foreshock and when it isn't, and as far as I know we really didn't have any particular warning for this earthquake.