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Nmss/Hlwrs, Cnwra, & Demps I S OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS (NMSS) DIVISION OF HIGH-LEVEL WASTE REPOSITORY SAFETY and CENTER FOR NUCLEAR WASTE REGULATORY ANALYSES (CNWRA) and DEPARTMENT OF EARTH, MATERIAL, AND PLANETARY SCIENCES (DEMPS) JOINT TRIP REPORT SUBJECT: Participation in the Geological Society of America Penrose Conference: Kinematics and Geodynamics of Intraplate Dextral Shear in Eastern California and Western Nevada (Al 06002.01.292.542) DATE/PLACE: April 21-26, 2005, Mammoth Mountain Inn, Mammoth Lakes, California AUTHORS: John A. Stamatakos, CNWRA David A. Ferrill, DEMPS Philip S. Justus, NMSS DISTRIBUTION: CNWRA NRC SwRI W. Patrick W. Reamer Record Copy B, IQS B. Sagar B. Meehan CNWRA Directors D. DeMarco CNWRA Asst. Directors E. Whitt CNWRA Managers T. McCartin D. Ferrill D. Higgs L. Gutierrez E. Collins L. Kokajko F. Brown K. Stablein M. Bailey J. Guttmann A. Campbell J. Rubenstone K. Compton A. Ibrahim M. Nataraja B. Leslie J. Trapp OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS (NMSS) DIVISION OF HIGH-LEVEL WASTE REPOSITORY SAFETY and CENTER FOR NUCLEAR WASTE REGULATORY ANALYSES (CNWRA) and DEPARTMENT OF EARTH, MATERIAL, AND PLANETARY SCIENCES (DEMPS) JOINT TRIP REPORT SUBJECT: Participation in the Geological Society of America Penrose Conference: Kinematics and Geodynamics of Intraplate Dextral Shear in Eastern California and Western Nevada (Al 06002.01.292.542) DATEIPLACE: April 21-26, 2005, Mammoth Mountain Inn, Mammoth Lakes, California AUTHORS: John A. Stamatakos, CNWRA David A. Ferrill, DEMPS Philip S. Justus, NMSS SENSITIVITY: Non-sensitive BACKGROUNDIPURPOSE: The Yucca Mountain site is in the zone of influence of the Eastern California Shear Zone and the western Nevada tectonic zone called the Walker Lane (Figure 1). Interpretations of the tectonics of the plate boundary and the Walker Lane are critical components of the DOE seismic and volcanic hazard assessments. Staff from NMSS and its contractors at CNWRA are reviewing the tectonic information at the proposed high-level waste repository at Yucca Mountain, especially with respect to how the tectonic information impacts current Department of Energy (DOE) information regarding the seismic and volcanic hazards at the Yucca Mountain site. This Penrose Conference provided an extraordinary opportunity to interact with the scientific community and to learn of the latest tectonic concepts applicable to hazard assessments of Yucca Mountain. In particular, the meeting fostered extensive information exchange on the range of geological and geophysical data that are used to discern how the Walker Lane accommodates tectonic strains from the North American plate margin coupled with mantle-crustal thermal-mechanical stresses, and how these data sets are being integrated into spatially and kinematically coherent and comprehensive models of crustal deformation through time. The meeting also provided the opportunity for staff to obtain peer comments from the larger scientific community on CNWRA studies in the region, and of the tectonic models currently considered important in our prelicensing evaluations of the DOE hazard studies for Yucca Mountain. 1 Figure 1. Digital Elevation Model of Western United States Topography with Annotations That Show the Locations of Site and Geologic Features Described In the Trip Report. 2 The meeting was attended by nearly five dozen scientists covering a range of geologic and geophysical disciplines, including tectonics, earthquake seismology, paleoseismology, geodesy, volcanology, tectonic geomorphology, paleoclimatology, tectonic sedimentology, and sedimentary basin analysis. There are no formal conference proceedings. The conference format is structured around keynote lectures (two per session topic) followed by moderator-led discussions. In addition to the keynote lectures and discussions, there were poster sessions each evening that also focused on the session topics. Finally, the conference included a one- day field trip that examined geologic evidence of fault-slip and deformation along the White Mountain, Queen Valley, and Coaldale faults. This trip report summary is based on our impressions from the informal presentations, unpublished abstracts and posters, and discussions held throughout the conference. The Technical Sessions and keynote lectures were: 1. Regional Plate Tectonic and Geologic Setting * Tanya Atwater (University of California at Santa Barbara): Plate tectonic reconstruction and late Cenozoic deformation budget of western North America * Brian Wernicke (California Institute of Technology): Geologic reconstructions 2. Eastern California Shear Zone-Geodesy and Geology * Rick Bennett (University of Arizona): Geodetic deformation rates in the eastern California shear zone * Doug Walker (University of Kansas): Slip Rates and slip gradients in the eastern California shear zone-the geology 3. Walker Lane Belt-Geodesy and Geology * John Oldow (University of Idaho): Crustal anisotropy, strain localization, and the development of transtensional strain partitioning during the late Cenozoic evolution of the central Walker Lane, western Great Basin * Jim Faulds (Nevada Bureau of Mines & Geology, University of Nevada at Reno): Kinematics of northern Walker Lane: An incipient transform fault along the Pacific-North American plate boundary 4. Links Among Climate, Tectonics, and Geomorphology * Eric Kirby (Penn State University): Tectonic insight from topographic observations: Does it really work? * Kelin Wipple (Massachusetts Institute of Technology): Tectonics and Topography: What's in it for me? 3 5. Interplay Between Magmatism and Tectonics * Allen Glazner (University of North Carolina): Space-time patterns of late Cenozoic magmatism in eastern California and western Nevada * Chris Henry (Nevada Bureau of Mines & Geology, University of Nevada at Reno): Coupled magmatic-tectonic evolution of the Walker Lane, western Nevada and eastern California 6. Recent Geodynamic Evolution of the Eastern California Shear Zone and Walker Lane Belt * Kevin Furlong (Penn State University): Lithospheric geodynamics of the eastern California shear zone * Gene Humphreys (University of Oregon): Walker Lane dynamics SUMMARY OF PERTINENT POINTS: The following paragraphs summarize some of the concepts, data, interpretations, and conclusions from the keynote sessions that are relevant to potential seismic and volcanic hazards at Yucca Mountain. We have focused on two main themes of the presentations, the application of geodetic measurements to hazard estimates and the nature and style of faulting in the southern Great Basin. Role of Geodetic Measurement In Hazard Assessments There is a general consensus among the participants that, throughout the Great Basin and Walker Lane, crustal strain rates derived from Global Positioning Satellite (GPS) geodetic data are higher than strain rates derived from geologic and paleoseismic information. This issue is important to Yucca Mountain hazard assessments because recent GPS data from Wernicke, et al. (2004) suggest significantly greater strain accumulation in and around Yucca Mountain than current estimates based on the geologic record that form the basis for current DOE seismic and volcanic hazard assessments. Several alternative explanations for the discrepancy between the geodetic and geologic strain rates were discussed. Transient Crustal Strain. Presentations on new GPS-derived displacement field data by B. Wernicke and GPS crustal models by K. Furlong suggest that geodetically-derived displacement data may reflect secular or time-transient behavior, perhaps related to post-seismic deformation within the earthquake cycle. In this explanation, the GPS data at Yucca Mountain record this short-term (10-100 yr) transient crustal strain. Such short term pulses would not impact the overall crustal strain patterns or hazard estimates because they are too short-lived to accumulate the necessary strains to generate earthquakes or induce volcanism. Geodesists need to do additional work to determine the nature of this time transient behavior which may be relevant to considerations of deformation at Yucca Mountain. 4 Episodic Crustal Strain. The GPS data are recording an episodic pulse of increased strain accumulation. If the pulse duration is sufficiently long (on the order of 104 to 10 5 yrs) then enough strain could accumulate in the crust to generate earthquakes or induce volcanism. In this case the geologic record records the average between the active pulses and inter-pulse low activity. However, if the Yucca Mountain area is currently within one of these higher-activity pulses, then the GPS data, not the geologic data, may yield a more reliable estimate of the hazard activity. Undetected Geologic Strain. Comparisons between GPS displacement rates and fault displacement rates show a discrepancy between displacement rates measured by these two approaches. The GPS rates are accurate but the geologic rates underestimate actual deformation because the data only reflect that component of faulting and volcanism that is known. The discrepancy between the GPS and geologic rates can be accounted for in either non-seismogenic features (i.e., fractures, penetrative deformation, or fault creep) or in present but undetected faults and volcanic features. Additional geological data are needed concerning displacements and displacement gradients on mapped faults, as well as off-fault displacements (e.g., small scale faulting, extension fracturing, dike intrusion, grain scale deformation). GPS Uncertainty. There is significant
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