From: km6e (Kirk Martini) To: afrankel@usgs.gov Subject: hazard maps and central Virginia Date: Thu, 24 Jul 97 08:49:10 EDT I have a question concerning differences in recent USGS hazard maps, specifically concerning the seismicity of central Virginia relative to Charleston SC. In the maps distributed with the 1994 NEHRP provisions, prepared by USGS, all the maps of spectral acceleration levels for a given probability level, show central Virginia on a level similar or even greater than Charleston. For instance, Map 5: 0.3 second response spectral acceleration with a 10% probability of exceedance in 50 years, shows Charleston in the range of 20 to 25 percent g, and the region surrounding Charlottesville and Richmond Virginia in the 20+ range. But, current maps available on the web show a different picture. The same category map on the web: http://wwwneic.cr.usgs.gov/eq/hazmaps/0503hz.gif also shows Charleston in the 20+ range, but the contours drop off much more quickly in the region of Charleston, with central Virginia in the range of 6 to 8, significantly lower than the level shown in the 1994 map. I'm curious to know the reasons underlying these differences. I teach a course at the University of Virginia concerning earthquake design, and the topic is of great interest to me and my students. Thanks very much, Kirk Martini __________________________________________________________________ . . . Kirk Martini . . Assistant Professor of Architecture and Civil Engineering . . . . Department of Architecture tel: 804-924-6445 . . 126 Campbell Hall fax: 804-982-2678 . . University of Virginia e-mail: martini@virginia.edu . . Charlottesville VA 22903 . . . . http://palladio.arch.virginia.edu/~km6e/ . __________________________________________________________________