|MadSci Network: Earth Sciences|
Dear Chelsie: By definition, the main shock of an earthquake is the highest Richter scale magnitude shock of the event - also called an earthquake cluster. An aftershock is of lower magnitude. A foreshock, also of lower magnitude, can occur prior to the main shock. All of these occur on or near the same fault or rupture zone in the Earth's crust. These three types of earthquakes can occur on a time scale of seconds to weeks apart. It is possible to feel the ground shaking in each of these, although foreshocks are generally of lower magnitude than aftershocks. Reference: USGS National Earthquake Information Center - http://wwwneic.cr.usgs.gov/ Rick De Van firstname.lastname@example.org
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