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RE: Z factor definition

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I would discuss with the soil's engineer what was considered in developing
the site specific ground acceleration.  If it's basis included the effects
of local soil type, nearby faults, etc, then use of the code coefficients
may be redundant.  But then I would compare my site-specific design
acceleration with the minimum code design acceleration as well. 

> -----Original Message-----
> From: Bob Hanson [mailto:Hansonb(--nospam--at)]
> Sent: Tuesday, October 26, 1999 9:47 AM
> To: Seaosc List EMAILto (E-mail)
> Subject: Z factor definition
> List,
> I would like clarity in defining terms related to Z in the UBC seismic
> formula.  As I understand it the Z is the estimated peak 
> horizontal ground
> acceleration (.4g for zone 4) on rock with a 10% probability of being
> exceeded in 50 years. I am looking at a site 1.5 km from a 
> type B fault in
> the LA basin on natural alluviam.In the soil report the 
> statement using
> identical terms states the acceleration as .55g. The soil 
> report basis is
> the National Seismic Hazard Mapping Project by the USGS. I 
> recognize that
> site specific soils play into this and my question is should 
> I use a Z value
> of .55? Are the C, N & S  factors for near source going to 
> ratchet the .55
> beyond intent?
> Thanks in advance,
> Bob Hanson