What are foreshocks and aftershocks?
“Foreshock” and “aftershock” are relative terms. Foreshocks are earthquakes which precede larger earthquakes in the same location. Aftershocks are smaller earthquakes which occur in the same general area during the days to years following a larger event or “mainshock.” As a general rule, aftershocks represent minor readjustments along the portion of a fault that slipped at the time of the main shock. The magnitude 5.0 Robinson Point earthquake of January 28, 1995 that occurred in the Seattle – Tacoma region was preceded by two “unfelt” foreshocks of magnitudes 0.7 and 1.8. Similarly, roughly twenty five “unfelt” aftershocks less than magnitude 2.0 occurred in the region after the M 5.0 earthquake. The frequency of these aftershocks decreases with time. Historically, deep earthquakes (>30km) are much less likely to be followed by aftershocks than shallow earthquakes. • Q: What’s the difference between a magnitude 4 and a magnitude 6 earthquake? A: Each step of one in magnitude is an inc
