Small foreshocks that precede a major earthquake can occur

Foreshocks may occur days, or even years, before the actual major earthquake itself.
Foreshocks are detected in almost half of all moderate to large earthquakes, and they are detected in over 70% of earthquakes that are above 7.0 in magnitude on the Richter scale. Foreshocks then lead to the main shock, which may be followed by after shocks, depending on the strength of the main shock.