From: Art Frankel 
To: martini@virginia.edu
Subject: seismic hazard maps
Date: Thu, 31 Jul 97 17:09:48 EDT

Kirk Martini,
  I was out of the office for a while and now I'm responding
to email. Sorry for the delay.
  One of the key differences between the 1996 USGS maps and the previous
USGS maps is the catalog of eastern U.S. earthquakes. We are now
using the NCEER catalog which has more accurate determinations
of magnitudes for pre-instrumental events. The previous USGS maps
used the best catalog available at the time, but it turns out
that this catalog systematically overestimated the magnitudes
of many pre-instrumental earthquakes. We have determined that this
catalog difference is the cause for the lower hazard values in many 
locations on the new maps (such as central VA) compared to the 
earlier maps. We have discussed this in the documentation (on 
the Web and USGS OFR 96-532), see section "brief comparison with 
previous USGS maps", as well as several workshops. Our new maps 
are consistent with site-specific studies done recently for nuclear 
power plants and bridges in the CEUS.
-Art Frankel