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RE: seismic maps

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Sorry, but I disagree....to an extent.
 
It may seem picky, but how often is post earthquake damage uniform across a neighborhood? I realize structure type, construction and many other issues affect the extent of damage but surely we are coming to understand the significant effects of soil strata and type.
 
This was brought home to me after seeing the effects of soft soils on damage to the (old) Nimitiz freeway in Oakland, CA. Specific sections were heavily damaged as a direct result of subsurface soil modification of EQ forces. It seemed pretty clear that there was a non-uniform zone of seismic activity. I realize this may be an oversimplication because there were different foundation systems employed, but it just strikes me that the geologists don't just make this stuff up. Soil factors have made their way into the code and while this may be perceived as the pendulum swinging too far for some I think it warrants some attention.
 
All this said, yes I am dubious about fine tuning to the extent of neighboring properties having significantly different design parameters. But I'm not opposed to being sensitized to areas of possible increased magnitudes when making engineering judgments about structural systems. (Somebody stop me!! - apologies to Jim Carey in The Mask)
 
Back to work Barry.
-----Original Message-----
From: Syed A Masroor [mailto:sam2000(--nospam--at)cyber.net.pk]
Sent: Thursday, December 20, 2001 12:11 AM
To: 73527.1356(--nospam--at)compuserve.com; list
Subject: seismic maps

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!

Excellent. No one could have said it better. Roger Turk makes the whole digest worth all our times.

S A Masroor