What Is a Pre-Earthquake?

A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space. The designation of an earthquake as foreshock, mainshock or aftershock is only possible after the full sequence of events has happened.

How do you know if an earthquake is a foreshock?

Foreshocks are earthquakes that precede larger earthquakes in the same location. An earthquake cannot be identified as a foreshock until after a larger earthquake in the same area occurs.

Does a small earthquake mean that a larger earthquake is coming?

"Every time a small earthquake happens, doesn't mean there is going to be a larger one," according to Chung. And if this sounds like a case of hindsight being 20/20, they already knew that. But this work does represent another piece of the prediction puzzle. "At this point it is more observational," said Trugman.