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The main purpose of this meeting was to begin discussion and planning for siting 20 additional strong-motion stations in the Wasatch Front area during FY2002 as part of the Advanced National Seismic System (ANSS).
Members Present: Steve Bartlett (chair), Bob Carey, Gary Christenson, Marv Halling, Mark Mainridge, Peter McDonough, Larry Reaveley, Barry Welliver, Boyd Wheeler, Les Youd
Members Excused: Rob Brantley, Chris Pantelides
Members Present from UUSS/ANSS Working Group: Walter Arabasz, Sue Nava, Kristine Pankow, Jim Pechmann (all from University of Utah Seismograph Stations, UUSS)
Agenda
1. Information Updates
2. Background information on existing strong-motion sites and urban-network status (Sue Nava)
3. Discussion and general planning for siting 20 new strong-motion stations in FY2002 (and creation of subgroup for follow-up decision making with UUSS/ANSS Working Group)
Minutes
1. Information Updates
Walter Arabasz reviewed information in the packets provided to committee members, calling attention to an insert titled, "Consensus Guidance for FY2002," which summarized key points from the committee's last meeting on July 26, 2001 (see Minutes, 7/26/2001). He continued with a brief report on (1) ANSS funding status (the amount appropriated by Congress for ANSS in FY2002 is $3.9 million, representing an increase of $300,000 above the FY2001 level, but still only about 10 percent of the authorized amount for ANSS) and (2) information on an upcoming workshop on instrumenting structures organized by the Consortium of Organizations for Strong-Motion Observation Systems (COSMOS) and scheduled for November 14-15, 2001, in Emeryville, California (Marv Halling will be the designated representative from Utah's advisory committee to attend the workshop, and Walter Arabasz will also attend).
Kris Pankow provided an overview of the Spectral-Analysis-of-Surface-Waves (SASW) technique for measuring near-surface shear-wave velocity. The SASW technique is becoming widely used for characterizing shear-wave velocities in the uppermost 30 meters, providing important information for ground-motion modeling. A collaborative proposal to apply the SASW method at selected sites in the Salt Lake Valley and neighboring parts of the Wasatch Front was recently submitted by the Utah Geological Survey (UGS) to the USGS/NEHRP funding program, but unfortunately was unsuccessful. The proposal involved Dr. James Bay, an assistant professor at Utah State University and an experienced practitioner of the SASW method.
Gary Christenson mentioned two reports prepared by the UGS relevant to characterizing near-surface shear-wave velocities: (1) Francis X. Ashland (2001). Site-Response Characterization for Implementing ShakeMap in Northern Utah, Utah Geological Survey Report of Investigation 248; and (2) an apparently formalized version of a final technical report submitted in 1999 to the U.S. Geological Survey by Francis X. Ashland and Kyle Rollins on Seismic Zonation Using Geotechnical Site-Response Mapping, Salt Lake Valley, Utah.
Steve Bartlett noted that he has submitted a proposal to UDOT to use the SASW technique at sites along the proposed Legacy Highway. The plan is to compare SASW measurements to in situ downhole data for local calibration of the SASW technique. Les Youd briefly described a proposal submitted to UDOT to install a downhole strong-motion array close to the I-15 bridge site near 2100 South in the Salt Lake Valley where strong-motion instruments were recently installed both on the bridge and in the free field nearby.
2. Information on existing strong-motion sites and urban-network status
Sue Nava reviewed information for strong-motion stations installed to date (during FY2000 and FY2001) in Utah's new urban network, and she described details available on the Web site of the University of Utah Seismograph Stations. Much information has been added to the homepage for Utah's Strong Ground Motion Monitoring Network (http://www.seis.utah.edu/urban/) has added much new information on the network, including varied maps (e.g., regionwide and by county) and extensive details for each site installation.
3. Discussion and general planning for siting 20 new strong-motion stations-Note: The following captures most of the salient discussion; the reporting is neither verbatim nor complete.
L. Reaveley: More stations needed in the downtown Salt Lake City area. Old South High School would be a good location. Also, consider an east-west array along 2100 South in the Salt Lake Valley; this area is becoming heavily industrialized.
L. Youd: Each instrument should have a purpose. There still is sparse instrumentation on soft valley sediments in the Salt Lake Valley.
Boyd Wheeler (UDOT): Would like to see a strong-motion instrument at every major interchange along the I-15 corridor in the Salt Lake Valley (lifeline issue). This includes, for example: (1) the junction of I-15 and the Bangerter Highway, (2) the I-215 "kickoff," (3) the junction of I-80 and I-15, (4) the downtown viaducts, and (5) the junction with I-215 and the proposed Legacy Highway in the Woods Cross area.
J. Pechmann and L. Youd: Need some more rock sites east of the Wasatch fault to capture attenuation on the footwall side of the fault-perhaps an east-west array up Little Cottonwood Canyon.
B. Welliver: Concern about instrumenting dams in canyons (such as Provo Canyon) where there is a downstream flooding hazard along the Wasatch Front. Separate from strong-motion instruments placed by the U.S. Bureau of Reclamation (USBR) on such dams, it may be important to have independent real-time monitoring for emergency response. (Cooperative arrangements are in progress between the USBR and UUSS to get rapid post-earthquake data feeds (with a latency of several minutes) from USBR strong-motion instruments to the UUSS recording center.
L. Youd: Partnerships with industrial operators such as Kennecott, Geneva Steel, and operators of oil refineries?
B. Carey: Comprehensive Emergency Management (CEM) is interested in information from the vicinity of the oil refineries because they're located at an important "gooseneck" in the Salt Lake Valley. Need to consider not only where population currently is but where it's heading--for example, Davis County, Utah County, the west side of Utah Lake, east up Weber Canyon.
L. Reaveley: Coverage in Tooele Valley also needs to be increased.
J. Pechmann: Extending instrumentation to the west is important because of potential earthquakes on the East Great Salt Lake and Northern Oquirrh faults. (B. Carey will explore possibility of instrumenting the Chemical Demilitarization Facility in Tooele Valley.)
L. Youd: Given historical seismicity in northern Utah (as well as potential rupture of the Brigham City segment of the Wasatch fault), would like to see an array extending west from Brigham City to Tremonton. Useful to try to get private industry to pay for some instruments. The Advisory Committee could write a letter-request to major industries in Utah seeking their help.
M. Mainridge: As a structural engineer, concerned that Salt Lake City isn't covered well enough yet.
L. Youd: Pioneer Park site suggested. Need one or two more sites in the high-rise area of downtown Salt Lake City. Should one be put in the State Capitol complex? Suggestion: Plan approximately 10 instruments in the Salt Lake Valley and 10 instruments elsewhere. In the Salt Lake Valley, need two to three instruments downtown, some along the 2100 South corridor, and some in a north-south profile on major interchanges along the I-15 corridor.
Before adjourning, the Advisory Committee created a subcommittee tasked with developing specific siting recommendations for at least 20 strong-motion instruments for FY2002 (selection of more than 20 sites is desirable in case alternatives are needed). The subcommittee will include: Steve Bartlett, Les Youd, Marv Halling, Gary Christenson, and Larry Reaveley. Sue Nava and Jim Pechmann from the UUSS/ANSS Working Group will work with the siting subcommittee.
The next meeting of the Advisory Committee was scheduled for Thursday, January 24, 2002--at which time the siting subcommittee will present its recommendations for approval by the whole Advisory Committee.
Minutes reported by Walter Arabasz and Jim Pechmann
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