U.S. Geological Survey Earthquake Hazards Reduction Program Final Technical Report Estimating Uncertainties of Seismic Hazard Parameters for Nevada Faults, Formations of a Nevada Quaternary Fault Working Group, and Gaining Consensus Fault Parameters Grant Award No. 06HQAG0126 Craig M. dePolo Nevada Bureau of Mines and Geology University of Nevada, Reno, NV 89557 (775) 784-6691 (775) 784-1709 FAX [email protected] Program Element: 1 Key Words: Paleoseismology, Quaternary Fault Behavior, Trench Investigations Abstract Twenty-two nationally recognized scientists, known as the Nevada Quaternary Fault Working Group, assembled and reviewed the current status of research on several of Nevada’s high risk faults, recommended seismic hazard values for faults when possible, and recommended future directions of research on major faults in Nevada. The Working Group met for two days in Reno and reviewed twelve of Nevada’s high-risk faults. Background reports for each fault were distributed to the scientists before the meeting. At the meeting each fault was reviewed, including relevant reports and studies, any known paleoearthquake history, estimated fault slip rates, estimated earthquake recurrence intervals, earthquake segmentation models, and estimated single-event displacements. The working group found that Nevada was still in the early stages of characterizing most of its high-risk faults, and more research and age determinations are needed to constrain seismic hazard parameters. Consequently, it was difficult for the group to determine many consensus fault parameters. The working group did, however, make a series of recommendations to help gain more information so that consensus values can be attained in the future. A follow-up meeting was strongly recommended by the group to review other high risk faults in Nevada, prioritize faults to be studied, and continue making recommendations for important studies. The initial recommendations presented here were developed at the meeting and reviewed by several working group members following the meeting. 1 Table of Contents Section Page Number Abstract 1 Introduction 3 Meeting Agenda 5 Recommended Research Priorities 7 Values used in the 2002 National Maps 13 Radiocarbon Dates 14 Genoa fault 20 Indian Hill fault 41 Carson City fault 49 Kings Canyon fault 58 Mt. Rose fault zone 66 Peavine Peak fault 83 Olinghouse fault zone 91 Pyramid Lake fault zone 104 Warm Springs Valley fault system 127 Las Vegas Valley fault system 143 Eglington fault 161 Black Hills fault zone 173 2 Introduction The Nevada Quaternary Fault Working Group was established to 1) critically evaluate the accuracy and completeness of the paleoseismic-trenching data, particularly with regard to earthquake timing, displacements, and fault slip rate, 2) assign consensus, preferred recurrence interval and vertical slip rate estimates with appropriate confidence limits to the faults reviewed, where the data is adequate to do so, and 3) identify critical gaps in the paleoseismic data and recommend where and what kinds of additional studies that should be performed to ensure Nevada’s earthquake hazard is adequately documented and understood. The Working Group members are: Nevada John Anderson, Nevada Seismological Laboratory John Bell Nevada Bureau of Mines and Geology Craig dePolo Nevada Bureau of Mines and Geology Jon Price Nevada Bureau of Mines and Geology Alan Ramelli, Nevada Bureau of Mines and Geology Tom Sawyer Piedmont GeoSciences Burt Slemmons UNR Emeritus Wanda Taylor UNLV Geoscience Department Steve Wesnousky UNR Center for Neotectonic Studies US Geological Survey Tony Crone Kathy Haller Suzanne Hecker Steve Personius Dave Schwartz Jim Yount External Larry Anderson U.S. Bureau of Reclamation Bill Bryant California Geological Survey John Caskey San Francisco State University Bill Lund Utah Geological Survey Susan Olig URS Tom Rockwell San Diego State University Ivan Wong URS 3 The Working Group convened in mid-November 2007 to review and assess the accuracy and completeness of the paleoseismic data available for eleven high- risk faults, and to make recommendations for additional research necessary to adequately understand and characterize these faults. The faults reviewed were: Reno-Carson City Urban Corridor Genoa fault Carson City fault Kings Canyon fault zone Indian Hill fault zone Mt. Rose fault zone Peavine Peak fault Olinghouse fault zone Pyramid Lake fault zone Warm Springs Valley fault system Las Vegas Urban Area Las Vegas Valley fault system Eglington fault (part of the Las Vegas Valley fault system) Black Hills fault zone This report includes the agenda of the working group meeting, the edited initial recommendations, and the background reports for the twelve faults that were supplied to the Working Group. 4 Nevada Quaternary Faults Working Group Meeting AGENDA November 19, 2007 8:00 Introduction, Agenda, and Purpose (dePolo) 8:10 Introduction and Purpose (USGS) 8:30 Utah Working Group Experience (Lund) 8:40 Estimating Two-Sigma Ranges and Uncertainties (Wong) 8:50 Goals, Approach, and Questions (dePolo) 9:00 Carson Range fault system Overview 9:05 Genoa fault 10:15 - BREAK - 10:45 Genoa fault (cont.) 11:00 Carson City faults (Carson City fault, Kings Canyon fault zone, and Indian Hill fault zone) 12:00 - LUNCH - 1:00 Mt. Rose fault zone 2:10 Carson Range fault system Earthquake Segmentation 2:30 - BREAK - 3:00 Peavine Peak fault 4:00 Las Vegas Valley fault system 5:00 Wrap-Up and Outstanding Issues 5:30 - ADJOURN - 5 November 20, 2007 8:00 Eglington fault 9:00 Black Hills fault 10:00 - BREAK - 10:30 Pyramid Lake fault zone 12:00 - LUNCH - 1:00 Warm Springs Valley fault system 2:00 Olinghouse fault zone 2:30 - BREAK - 3:00 Olinghouse fault zone (cont.) 3:30 Planning Special Consideration Zones 3:45 Prioritizing Identified Earthquake Research 4:15 Prioritizing the Next Faults for the Working Group to Review 4:30 Wrap-Up and Outstanding Issues 5:00 - ADJOURN - 6 Nevada Quaternary Fault Working Group Initial Recommendations for Research Priorities for studies of Quaternary Fault in Nevada The level of knowledge needed to reasonably characterize the large hazard and risk associated with Nevada’s major active faults is inadequate and requires an aggressive effort to acquire the geoscience data necessary to evaluate the seismic hazard to Nevada’s urban centers. These data can then be used by scientists, planners, and government officials to aid in adopting practices appropriate to enhance the safety of Nevada’s citizens. These are termed “initial recommendations” because a follow-up meeting is needed to further debate, refine, eliminate, and add to these comments. Divergent views exist among the Working Group members on the relative importance of some of these ideas. Further discussion is needed before these recommendations can be prioritized, and there are other high-risk faults in Nevada that need to be reviewed by the Working Group to explore whether there are additional recommendations. Planning Special Consideration Zones The State of Nevada should develop a strategy to create Planning Special Consideration Zones that will allow for safe development with respect to potentially hazardous earthquake faults. With input from design, engineering, and geoscience professionals, the creation of these zones will guide land-use planners, building officials, and developers in minimizing the adverse effects of fault surface rupture and other earthquake-related hazards. The late Quaternary faults in Nevada urban areas should then be mapped and zoned at a scale of 1:24,000 using the developed strategy. Northern Nevada General Needs for Northern Nevada Abundant information related to late Quaternary faulting and surface ruptures likely exists in a variety of unpublished reports and documents prepared by consultants and construction firms in the Reno-Carson City urban corridor. The contents of these reports could provide new insight into the activity rates or ages of surface ruptures on various fault zones or strands. The working group recommends that an effort be made to systematically poll geoscience consultants in the area, and to collect and archive non-proprietary reports that contain information relevant to fault activity and related hazards. This archive should be based at a state agency where the information will be publicly available. 7 Mt. Rose fault zone The Mt. Rose fault zone includes the Washoe Valley fault zone, the Little Valley fault, and the Virginia Lake fault zone. Currently available paleoseismic data are inadequate to characterize the times of prehistoric large earthquakes along the fault zone. The close proximity of this fault system to the Reno-Carson City urban centers makes its study a priority. The only compelling constrains on paleoearthquakes on the Mt. Rose fault zone from existing data are that two surface-rupturing earthquakes have occurred since about 1,553-1,862 cal. yr BP. Geological and geophysical studies are needed to develop paleoseismic records of earthquakes for the major strands of the zone. These records can be developed by first systematically mapping of fault strands and determining the ages of various faulted deposits. These studies can yield valuable information about long-term slip rates and the time of the most recent event. Geophysical and subsurface studies may be helpful in defining the down-dip and along-strike links between various strands. Eventually, trenching studies at selected sites will be required to define critical parameters such as displacement per event, the times