Re: How do I find the richter magnitude of a recorded earthquake?

As you know, the Richter scale indicates the energy released by an 
earthquake, approximately. This is roughly the base 10 logarithm of the 
maximum amplitude of ground motion where the earthquake happened so if 
you can convert your simulation results to ground motion you will be able 
to calculate "your own" Richter values. Without more information on how 
your simulation works I can't offer more specific suggestions.

One thought: It might be more instructive to sum over the entire event 
the square of the amplitude at 1/100th sec intervals (for example) to 
record the total energy released.  

Richter and other seismic energy scales are pretty complicated -- as are 
earthquakes -- so you might make good progress by reading the USGS web 
site, beginning for example here: 
 http://earthquake.usgs.gov/learning/faq.php?categoryID=2