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RE: seismic forces

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As Gordon has pointed out, most of the U.S. seismic parameters are based on an effective 2500 year return period which were derived from probabilistic studies and formula.  As you get to the western part of the U.S. where we have known faults these values were transitioned with deterministic values based on actual seismic data (i.e. seismic acceleration recordings).  It is probably closer to say your seismic values are about the same (may be may be not, I did not look them up) and the people in Sikestone and Summerville are now getting hosed.

Thomas Hunt, S.E.

"Gordon Goodell" <GordonGoodell(--nospam--at)>
11/24/2008 02:24 PM
Please respond to seaint
RE: seismic forces

10% has been abandoned; now it’s 2/3 of 2%, 50 yrs.  That’s a 2500 yr return!  So in California, where the frequency of a design event is more like a few hundred years, known faults that have enough historical data use 1 ½ x the characteristic event.  There’s a good, brief  discussion of the rationale behind this change in the commentary to the Ground Motion chapter of the 2003 NEHRP.
Gordon Goodell
From: David Topete [mailto:d.topete73(--nospam--at)]
Monday, November 24, 2008 2:39 PM
Re: seismic forces

Aren't the accelerations based on the 10% at 50 year event?  So, that means New Madrid and Summerville have the potential for very large accelerations for the 475-year event.  The fact that the Hayward fault (which I live on) is more active is because you have the Pacific plate rubbing constantly on the North American plate, or vice versa.  If I'm off, I'm sure I'll be corrected.  That's my just my view from basement...
On Mon, Nov 24, 2008 at 12:19 PM, SGE Structural <sgordin(--nospam--at)> wrote:
Based on the 2006 IBC (ASCE07-05), the seismic accelerations for Hayward, CA (right on the Hayward fault) appear to be about 60% lower than those for Sikestone, MO, and about the same as for Summerville, SC.  
Historic (1812 and 1886) considerations aside, any comments?
V. Steve Gordin, SE
Irvine CA

David Topete, SE

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