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# Re: California Earthquake Problems

• To: seaint(--nospam--at)seaint.org
• Subject: Re: California Earthquake Problems
• From: Sleiman Serhal <mony(--nospam--at)destination.com.lb>
• Date: Thu, 14 Jan 1999 10:24:29 +0200

```>
> > Maybe richter scale magnitude isn't very relavent.
>
One thing that make Richter magnitude irrelevant is that it is, by
definition, the magnitude of the earthquake at a distance of 100Km from
the epicenter. So if your house is right above the fault or at 300Km
from it, the earthquake would still be defined as for example ML=7.0.
Whereas the intensity scale, such as Mercalli's, is descriptive of the
amount of damage and how people sensed the earthquake, so the house
above the fault would get a higher intensity rating than the house at
300Km from the epicenter. Older codes, at least European ones, used
Intensity scales (such as the Echelle Macrosismique Internatinale) for
seismic design and not Magnitude scales. The new European codes switched
to a Zoning system similar to UBC's in 1992.

I usually get annoyed by owners and even engineers who ask me to what
Richter scale I designed a structure, because when I tell them that the
Richter scale is not used in seismic design, they assume that I'm
avoiding to answer them or that I'm not a qualified Engineer !

>
> "The peak ground accelerations corresponding to these two periods can be used
> to construct a site-specific response spectrum similar to the generalized one
> at the end of Chapter 16 in UBC.  The flat part of the spectrum is defined by
> Sa = 2.5*PGA@0.2sec <mailto:2.5*PGA@0.2sec> , and the curved part by Sa =
> PGA@1.0sec/T."
>
> I wonder what is the percentage of structural engineers who understand the
> above procedure without spending a considerable amount of time studying and
> trying to figure out what it all means and attempting to fit it to another
> similarly simple equation from the people who have created it, and attempting
> to fit it to another ... etc.
>

Very true !

Moni Serhal, MSCE

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