foreshock

American  

[fawr-shok, fohr-] / ˈfɔrˌʃɒk, ˈfoʊr- /

noun

Geology.

1. a relatively small earthquake that precedes a greater one by a few days or weeks and originates at or near the focus of the larger earthquake.

---

foreshock British  

/ ˈfɔːˌʃɒk /

noun

1. a relatively small earthquake heralding the arrival of a much larger one. Some large earthquakes are preceded by a series of foreshocks Compare aftershock

---

Etymology

Origin of foreshock

First recorded in 1900–05; fore- + shock ¹

Example Sentences

But conventionally, only half of earthquakes have an easily detectable foreshock, while the other half do not.

From Los Angeles Times • Dec. 22, 2025

This may have been a foreshock - an early release of energy - but it is not a predictor of exact timing of a future earthquake, explained Prof McNeill.

From BBC • Jul. 30, 2025

In 1970, there was a magnitude 5.2 quake with a 4.0 foreshock close to the same location, she said.

From Seattle Times • Jan. 5, 2024

It’s not clear that a quake is a foreshock until a larger quake happens.

From Scientific American • Jul. 20, 2023

The downfall of the Fox host Bill O'Reilly in April 2017 turned out to have been just a foreshock of the changes to come.

From New York Times • Oct. 23, 2018