[CEUS-earthquake-hazards] Revised seismic design criteria for New Madrid

[Nicolas Luco]

Just to clarify, the quote  "the 2008 USGS hazard maps should not be 
substituted for the model building code design maps nor should they be
used with ASCE/SEI 41 or 31 for seismic rehabilitation or evaluation" is 
not from the Building Seismic Safety Council (BSSC) proposal for updated 
seismic design criteria 
(http://www.bssconline.org/2nd09MOballot/Proj07props/ProposalSDPRG-1R4_07-07-08_Final.pdf), 
but rather from the USGS webpage 
http://earthquake.usgs.gov/research/hazmaps/products_data/2008/disclaimer.php. 
 The full text from that webpage is pasted here:

Important Note on Use of New 2008 USGS Hazard Maps
Although it is anticipated that the new 2008 USGS hazard data will be the 
basis for the seismic design maps in future editions of the NEHRP 
Recommended Provisions, the ASCE/SEI 7 Standard, and the International 
Building and Residential Codes, the values on those seismic design maps 
are expected to be materially different from the values on the 2008 hazard 
maps. More specifically, it is anticipated that ? 
1.      the USGS hazard values will be amplified by factors that convert 
(approximately) to spectral response accelerations in the maximum 
direction of ground motion, 
2.      these factored hazard values will be multiplied by ?risk 
coefficients? that adjust for a target risk (namely 1% probability of 
collapse in 50 years), and 
3.      these factored and adjusted hazard values will be capped near 
known active faults by so?called deterministic ground motions (like the 
USGS hazard values were for the design maps in current editions of the 
model building codes). 
Thus, the 2008 USGS hazard maps should not be substituted for the model 
building code design maps nor should they be used with ASCE/SEI 41 or 31 
for seismic rehabilitation or evaluation. 
For more information, please click on the following link to a recap of the 
Building Seismic Safety Council (BSSC) Seismic Design Procedures 
Reassessment Group (SDPRG -- a.k.a., Project ?07) Workshop .

This note was co-drafted by the USGS, FEMA, and BSSC to remind engineers 
that while USGS hazard maps are the basis for design maps in model 
building codes, hazard and design maps are not one in the same (for 
example, due to the capping mentioned in note #3 above).  This was true of 
the 1996 and 2002 USGS hazard maps and the building code design maps 
derived from them, and it continues to be true (more so, in part due to 
notes #1-2 above) for the 2008 USGS hazard maps and the design maps 
anticipated for the 2009 NEHRP Recommended Provisions, 2010 ASCE 7 
Standard, 2012 International Building and Residential Codes, and next 
editions of ASCE/SEI 41 and 31.

Please let me know if you have any questions/comments.

----------------------------------------------------------------------------
Nicolas Luco, PhD
Research Structural Engineer
U.S. Geological Survey

Mailing Address:
PO Box 25046, MS 966
Denver, CO 80225

Physical/Overnight Address:
1711 Illinois Street, Room 426
Golden, CO 80401

Phone: (303)273-8683
Fax: (303)273-8600
----------------------------------------------------------------------------




Seth Stein <seth at earth.northwestern.edu> 
Sent by: ceus-earthquake-hazards-bounces at geohazards.usgs.gov
01/14/2009 12:13 PM
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Subject
[CEUS-earthquake-hazards] Revised seismic design criteria for New Madrid






Readers may be interested in the latest proposal for seismic building
design criteria. In it "the 2008 USGS hazard maps should not be
substituted for the model building code design maps nor should they be
used with ASCE/SEI 41 or 31 for seismic rehabilitation or evaluation."

Specifically, there are a set of scale (risk) factors to apply to the
2008 USGS hazard maps to produce design maps: "Resulting risk
coefficients are generally 0.85-1.15, but as low as 0.7 near New Madrid
and Charleston".

The USGS disclaimer

http://earthquake.usgs.gov/research/hazmaps/products_data/2008/disclaimer.php 



gives  information about how the hazard maps are modified to
produce design maps. For additional information, see

http://bssconline.org/2008AnnualMeeting/080910--Luco1@BSSC_Annual_Mtg(Posted).pdf

http://bssconline.org/2008AnnualMeeting/08MeetingRecap.html
-- 
Seth Stein
William Deering Professor
Department of Earth and Planetary Sciences
1850 Campus Drive
Northwestern University, Evanston, IL 60208
(847) 491-5265 FAX: (847) 491-8060 E-MAIL: seth at earth.northwestern.edu
http://www.earth.northwestern.edu/people/seth

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