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RE: Northridge Earthquake a Major "Event"

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You can pretty much say this about any earthquake with magnitude larger than
6.0. There are some areas that will experience large shaking intensity, and
some that won't, depending on the location and type of fault. The point that
Lynn is bringing up, and is valid in my opinion, is that Northridge was a
code level design basis earthquake, for life safety purposes, for a large
portion of the area that was affected by it. Its strong shaking tested many
types of buildings, from single family wood frame to multistory steel and
concrete buildings. 

We learned a substantial amount of new information (steel moment
connections) and it reaffirmed old flaws that we already knew about
(softstory). We applied the new and old information to the code in the form
of changes in 97 UBC as much as we could. And we will continue learning more
with each subsequent major event. However, I don't think we can dismiss
Northridge as just another minor shaking and continue speculating what would
happen if we REALY get a major quake.  

Ben Yousefi, SE
San Jose, CA

	-----Original Message-----
	From:	Ron O. Hamburger [SMTP:ROH(--nospam--at)eqe.com]
	Sent:	Monday, October 04, 1999 9:38 AM
	To:	seaint(--nospam--at)seaint.org
	Subject:	Re: Northridge Earthquake a Major "Event"





	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.