The Flinn-Engdahl number is very useful in earthquake searches. We often will
select a larger area with the FE# and then refine the search here. One thing to
remember, however is that the FE regions are fairly gross. They are defined
on 1 degree latitude and longitude changes. That is, for example a search for
FE region 479 (Colorado) would give good results but one for Virginia (with rugged
state boundaries) might not.
The search mechanism on the NGDC web site for the NEIS data uses (in the
background) FE regions. The site is:
http://dev.ngdc.nndc.noaa.gov/cgi-bin/wt/nndcp/ShowDatasets?dataset=101155&search_look=5&display_look=10000,6,10003,10002

Select California-Nevada border region for example and you are actually
searching FE region 40.