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Re: Near source factor for City of Newport, Oregon[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: Re: Near source factor for City of Newport, Oregon
- From: "Swingle, Mark" <Mark.Swingle(--nospam--at)dgs.ca.gov>
- Date: Fri, 12 Nov 1999 14:35:07 -0800
- Cc: "'mswingle(--nospam--at)earthlink.net'" <mswingle(--nospam--at)earthlink.net>
Friday, November 12, 1999 Curt and David, PERHAPS the reason both Na and Nv are equal to 1.0 in southern Oregon is because the subduction zone is more than 15km off the coast for all of southern Oregon. The only area in California where it is nearer to the coast than 15km is at Cape Mendocino (according to "Maps of Known Active Fault Near-Source Zones in California and Adjacent Portions of Nevada", published by ICBO, prepared by CA Division of Mines and Geology (CDMG), February 1998). I believe the subduction zone does not come nearer in southern Oregon, but you'd better check for yourself. To qualify as Type B (at a minimum), a fault must be believed capable of a magnitude M6.5 or larger earthquake (regardless of slip rate), -OR- it must have a slip rate greater than 2 mm per year (regardless of magnitude). Type A faults have an even stricter requirement (must have a potential magnitude >= M7.0 -AND- a slip rate >= 5 mm per year). See 97 UBC Table 16-U. According to the above publication, the subduction zone (at least the portion off the coast of California) is capable of a magnitude M8.3, and has a slip rate of 35mm per year (I assume that means perpendicular to the fault trace?). This would make it (easily) a Type A fault. No other Type A or Type B faults are shown crossing the border from CA to OR. Also, note that no maps were produced for Oregon and Washington because there were no areas of Zone 4 in those states, not necessarily because there were no Type A or B faults. See also footnote 1 of 97 UBC Table 16-U. This says that "Subduction sources shall be evaluated on a site-specific basis." Without further guidance, I don't know what this means. Perhaps some geotechs would recommend a wider "near-source zone" based on the high expected magnitude of the only known subduction zone in UBC-land. You can contact the CDMG at 916-445-1923 for technical questions on this publication. Mark Swingle, SE Oakland, CA ------------------- From: "La Count, Curt" <Curt.LaCount(--nospam--at)Jacobs.com> To: seaint(--nospam--at)seaint.org Subject: FW: Near source factor for City of Newport, Oregon Date: Friday, November 05, 1999 David, Although Oregon has made parts of the coast zone 4, the Na and Nv factors are set to 1.0. I am not sure of the reasoning, but that's the code. Curt La Count Jacobs Engineering Portland, OR ------------------- From: David Hall To: seaint(--nospam--at)seaint.org Subject: Re: Near source factor for City of Newport, Oregon Date: Thursday, November 04, 1999 9:55AM Good question, I have a building that will be constructed in Brookings Oregon, and I will have to find the same thing. For those of you who do not know, Oregon adopted the 1997 UBC with Amendments with one of those being that the coastal are of Southern Oregon Be Zone 4. I was going to contact SEAOC, but if anyone knows, I would also be interested. David A. Hall, S.E., P.E. Senior Structural Engineer David Evans and Associates, Inc. 2828 SW Corbett Ave Portland, OR 97201 503-499-0280 Fax 503-223-2701 E-Mail dahl(--nospam--at)deainc.com
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