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Re: Northridge Earthquake a Major "Event"

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With regard to Lynn Howard's discussion as to whether the Northridge
Earthquake was a "code level" event - the determination really rests on
several things:

1- What site are you talking about.  Any earthquake produces a broad range
of intensities, ranging from very intense motion (near the epicenter and on
soft sites) to moderate, weak or imperceptible motion, further from the
causative fault.

2- At many sites directly north of the epicenter, for example, Santa
Clarita, San Fernando, etc, the response spectrum for the ground shaking
was far in excess of that contained in the code as a Design Basis
earthquake.

3- For many sites in Sherman Oaks, and other towns at the south end of the
Valley, the response spectrum for the ground shaking was approximately
equal to the code Design Basis earthquake.

4- For most other sties, the ground shaking was far less than the DBE.

Although ground shaking from the Northridge earthquake was locally very
intense, it also had short duration.  For a truly large magnitude
earthquake, such as the 1857 Fort Tejon, 1906 San Francisco, 1964 Prince
William Sound, ground shaking can last several minutes, not 15 or 20
seconds.  The Northridge earthquake was neither a code or "major" event,
from this perspective.