Definition of "foreshock" [foreshock]

• A minor tremor of the earth that precedes a larger earthquake originating at approximately the same location. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "If the team's results are correct, then this swarm is probably not a foreshock of something larger on the Hayward Fault."
• "When we get a swarm like the one in Berkeley, it doesn't come with a tag that says it is a foreshock."
• "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."