Re: How can you tell the difference between an Earthquake and an Aftershock.

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
rdevan@rtd1.com