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Re: RE: Seismic Zones in Texas

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Gentlemen, it seems relisting a FAQ draft from Mr. Perkins, who is part of the
Golden Colorado Project (Frankel's Project) may be appropriate:

Mr. Dave Perkins of USGS was also kind enough to send me a copy of another
proposed FAQ on the above subject which they may post in their website (
http://geohazards.cr.usgs.gov/eq/faq ).  I though those on this list may find
it interesting.  Also, perhaps, some of you may share some insights on this
issue which I hear has going on for some time on capped vs. uncapped maps
**********
Edward

There are two sets of maps:

1. The national probabilistic ground motion hazard maps. These are
straiaght probabilistic ground motion and HAVE NOT BEEN CAPPED.

2. The maps prepared by the USGS Golden GIS staff, supervised by members of
Frankel's group, according to the recipe given by FEMA-BSSC subcommittees,
to be used as design maps in the FEMA Recommendations for Seismic Standards
for New Construction.

The FEMA-BSSC recipe includes capping the ground motions on the maps in
such a way that the resulting design ground motions do not exceed the
largest values in the previous code, EXCEPT that when deterministic ground
motions from faults exceed the cap values, the deterministic ground motions
appear on the map.

The maps used as a basis for the code maps are the 2 percent probability of
exceedance spectral acceleration maps for 0.2 and 1.0 sec period, but
recontoured so that certain contours correspond to break points in the
code. Design values are 2/3 of the map values. The result (in uncapped
areas) is that design values are approximately 500-yr return period ground
motions in the west and approximately 1000-yr return period ground motions
in the east.

I hope this clears up your question. Maybe we should be distinguishing
between national hazard maps and national design maps.

At the site we have put up ONLY the uncapped maps. FEMA is publishing the
capped maps. The California/Nevada maps at the site represent only a "zoom
in" on that part of the maps. (bold added by ed gonzalez)


>>> Roger Turk <73527.1356(--nospam--at)compuserve.com> 01/08/99 07:49AM >>>
No, Ken, you are not getting old and afraid of change.  You are getting wiser 
in your older age.

What is happening is what Henry Petroski describes as the 30 year (or 35 
year) syndrome.  Since 30 to 35 years is the approximate working life of an 
individual, what he/she has learned *not* to do in that time, and the reasons 
for it, has not been adequately passed down to the younger members of the 
profession, they *don't* know what experience has shown to be inadequate.  
Therefore, we start having a series of failures every 30 - 35 years.

Compound this with educators that have had little or no practical experience 
who rely on computers that spit out answers in accordance with the 
instructions that *they* put into the computer and we are in for some *big* 
problems.

In the early 1960's it was a real chore to get masons to put reinforcing in 
masonry, at least here in Arizona.  ("All we need is a header every 5 courses 
and the wall is not going to go anywhere.")  Finally we were able to get 
masons to accept the need for reinforcing, however, the new masonry codes 
erode this requirement for seismic zone 2 locations by extrapolating tests 
that were intended only for small, single story, lightly loaded masonry 
construction to all masonry construction in seismic zone 2.

The USGS Seismic maps are not gospel.  Depending on how the head of the USGS 
seismic branch wants to have the maps look will depend on what we see.  
Algermissen's first map (1971), based on historical seismicity, was quite a 
bit different than his second map (ca. 1985), based strictly on probability 
(and politically modified), which is quite a bit different than Arthur 
Frankel's map (ca.1990's), which is based on a combination of probability and 
historical seismicity, which is quite a bit different from his map that 
doesn't have the accelerations divided by 4.  Have you seen the USGS map that 
shows California accelerations of 3.9g?  I would venture to say that very few 
people have.

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

Ken Tarlow wrote:

. > Is anyone else thinking this will be a disaster? or am I just getting
. > old and am afraid of change.