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RE: IBC 2000 Seismic maps

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Exactly my point!

Can anyone *guarantee* that spectral accelerations are going to vary in 
accordance with contours spaced a mile apart?  Just because some computer 
somewhere can calculate imaginary responses to imaginary point source 
earthquakes which have been reduced significantly from the actual spectral 
accelerations calculated from the same imaginary point source earthquakes 
(read the fine print in the upper left corner of the spectral acceleration 
maps) doesn't mean it is correct.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Barry Welliver wrote (concatenated posts):

. > The IBC maps have contour intervals as close as 1 mile or less within the
. > Salt Lake Valley. The need is to have a better reference scale than is
. > presently given in the 1:3,500,000 IBC

. > Barry H. Welliver

. > I hit send before I commented on your thoughts Roger.

. > I agree, the way we used to do things gave us very generalized magnitudes.
. > I'm not sure I disagree however with the tendency to fine-tune the shaking
. > intensities given the very localized damages seen in some recent
. > earthquakes. (Loma Prieta, Napa Valley). This combined with efforts to
. > understand local soil profiles for instance has produced some mapping work
. > which helps one feel a bit better about these new lines drawn in the IBC.

. > The long and short of it for me is to gear up for this known direction in
. > seismic design and try to make some sense of it all. I think I've spent as
. > much time this past year trying to figure out geology as I have in
. > understanding the new structural provisions.

> -----Original Message-----
> From: Roger Turk [mailto:73527.1356(--nospam--at)]
> Sent: Tuesday, December 18, 2001 3:58 PM
> To: seaint(--nospam--at)
> Subject: RE: IBC 2000 Seismic maps
> Barry Welliver wrote:
> . > I have this also, but the files are pdf format and we were looking for
> . > something over which we could lay a county and possible street map.
> IMO, when your spectral accelerations are dependent on the street
> where you
> live, or what your zip code is, they are too precise to have any accuracy!
> Even the lines on the seismic zone maps in the UBC showing the
> boundaries of
> the seismic zones are probably at least 10 miles wide so any
> place near the
> boundary can easily be on either side of the boundary.
> A. Roger Turk, P.E.(Structural)
> Tucson, Arizona

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