From: Charles Greenlaw <cgreenlaw(--nospam--at)speedlink.com>
Date: Thu, 25 May 2000 17:02:57 -0700
At 11:05 AM 05/25/2000 -0400, Roger Turk wrote:
>Everything about seismic zoning is fictitious!
>Then, someone suggested that Z reflect the seismic zone so that it would be
>easier to remember, so for Zone 4, Z = .4; Zone 3, Z = .3; Zone 2B, Z = .2;
>Zone 2A, Z = .15; Zone 1, Z = .1, and all the other factors adjusted so that
>the answers came out the same as previously.
A federally-funded 1978- vintage NEHRP precursor, ATC 3-06,
"suggested" this way, and the 1982-88 SEAOC Seismology Committee followed
suit, for the 1988 UBC seismic sections. Reportedly there was code
adoption-endangering "political" resistance in Zone 2 territory in the US
Midwest to the O.2 factor, and as a sop to them, a member of Seismology
Committee in the fall of 1986 offhandedly suggested dividing Zone 2 into A
and B portions, with the reduced value in the eastern portion (2A) that you
have noted. This gambit was embraced eagerly, and it worked.
There was no known technical research whatsoever as backing for the Zone 2
split or the .15 factor. This I know, because I was the one who suggested
the idea in committee.
It's hard to tell what in seismic code isn't fictitious or hastily
concocted, and then sold as solid, accurate science and time-proven wisdom
to eager believers.
At least this Zone 2A stunt didn't add needless workload to code users, or
add interpretation quandaries. To my amusement, Zone 2A has sprouted up in
Arizona and Hawaii since originally appearing east of the Rockies.
Charles O. Greenlaw SE Sacramento CA