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RE: California Earthquake Problems

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Paul, while I agree in principle with your suggestion to use ground
accelerations as a yardstick, we know from the experience in Northridge
that the more we instrument, the higher the recorded accelerations.  I
was told once that this is because there are a lot of local anomalies in
ground motion characteristics, so the closer we look (i.e., the more
instruments we put out there) the greater the liklihood that these will
be picked up. The earthquake is still the same, so correlations of
ground motion with damage with magnitude are always somewhat suspect.
Unfortunately, in my view, these higher recorded accelerations drive the
code-smiths to ever higher static lateral force coefficients, which
results in lots of money being poured into foundation systems to prevent
buildings from overturning or flying away.

J. Silva

> ----------
> From: 	Paul Feather[SMTP:pfeather(--nospam--at)]
> Reply To: 	seaint(--nospam--at)
> Sent: 	Wednesday, January 13, 1999 9:24 PM
> To: 	seaint(--nospam--at)
> Subject: 	Re: California Earthquake Problems
> Dear Yank
> The average person, as you say, has no idea what to expect from a
> "x.x"
> earthquake.
> All they have is a perception of the earthquake and its results
> derived from
> TV coverage highlighting as many high profile sensational images as
> possible.  Disaster sells.
> The very basis of what you propose is erroneous.  The effect on your
> house
> from a specific magnitude earthquake will depend on a multitude of
> variables; distance, direction, geology....  The end result being that
> the
> Richter magnitude is relatively meaningless in any credible discussion
> of a
> specific site (i.e. your house).  What is measurable is the ground
> acceleration experienced at a specific location and the resulting
> damage to
> the structure.
> The solution to this dilemma would be to educate the media to stop
> pushing
> key words like Richter scale, and start reporting recorded ground
> accelerations.  Then, we can hold a credible discussion based on
> physics and
> science.
> Paul Feather