This might be a dumb question, but how do they differentiate an "aftershock" from an "earthquake?" At what point would it be considered a separate earthquake from the first, rather than an aftershock?
Having some personal experience with these, I can assure you they both feel the same.
The exact definition is somewhat fuzzy.
http://www.newton.dep.anl.gov/newton/askasci/1993/general/GEN004.HTM
I don't know, and I know that aftershocks can be just as strong or stronger than the original, but I think it must have to do with where the epicenter is located. If it's a substantial distance from the first one, it may be considered a separate quake.
If they have one greater than 8.8 in a set time period, it will be the main quake and all of this will become foreshocks. At least that is the way I understand it.
This might be a dumb question, but how do they differentiate an "aftershock" from an "earthquake?" At what point would it be considered a separate earthquake from the first, rather than an aftershock?
In very general terms (and without the very specific details that scientists may use) ... it's a lesser earthquake than the main and initial one, and it's one that is part of the "swarm" of earthquakes that continue for a while after that main one -- during which times things are "settling down" and "readjusting" to their new positions.
There are a lot of adjustments being made underground during this time and that's what all these earthquakes are... the "settling down adjustments".
The first and second earthquakes occurred in Arkansas (December 16, 1811 - two shocks - Mfa 7.2, MSn 8.5 and Mfa 7.0, MSn 8.0) and the third and fourth in Missouri (January 23, 1812, Mfa 7.1, MSn 8.4; and February 7, 1812, Mfa 7.4, MSn 8.8). Otto Nuttli, however, has postulated another strong earthquake in Arkansas on December 16 at 18:00 UTC (MSn 8.0). This would make a total of five earthquakes of magnitude MSn 8.0 or higher occurring in the period December 16, 1811 through February 7, 1812.
--U.S. Geological Survey
It has to do with the location of subsequent quakes relative to the initial quake. If subsequent quakes are located within a small distance to the original, it is considered an aftershock.