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RE: Northridge Earthquake a Major "Event"[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: Northridge Earthquake a Major "Event"
- From: "Yousefi, Ben" <Ben.Yousefi(--nospam--at)ci.sj.ca.us>
- Date: Mon, 4 Oct 1999 15:45:28 -0700
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.
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