Title: 2018 Working Group on Nevada Seismic Hazards: Summary and Recommendations of the Workshop, February 5–6, 2018
Authors: Rich D. Koehler and John G. Anderson
Series: Open-File Report 2019-02
Format: 44 pages, color
Ranked by the numbers of tectonic earthquakes, Nevada is the third most seismically active state in the United States, behind Alaska and California (Anderson and Miyata, 2006). Major earthquakes in Nevada (dePolo et al., 1997) have included the 1915 Pleasant Valley earthquake (Mw7.2), the 1932 Cedar Mountain earthquake (Mw7.1), and the 1954 cluster of earthquakes in central Nevada including Stillwater (Mw6.8), Fairview Peak (Mw7.1), and Dixie Valley (Mw7.0) earthquakes. While these earthquakes have all fortunately been relatively removed from major population centers, these earthquakes, as well as widely distributed smaller earthquakes throughout the state demonstrate that the seismic hazard of the region is high. The U.S. Geological Survey (USGS) has consequently and appropriately been highly concerned that the National Seismic Hazard Map (NSHM) for this region should be as reliable as possible.
Seismic hazard in western Nevada is characterized by two main tectonic elements, the Walker Lane Belt (WLB) and Basin and Range extension. The WLB is characterized by transtensional strike-slip motion along the eastern side of the Sierra Nevada block at 6–9 mm/year to the NW relative to central Nevada. This motion is accommodated along northwest striking right-lateral faults, northeast striking left-lateral faults, and north-northeast striking normal faults (Stewart, 1988; Wesnousky, 2005a, 2005b; Wesnousky et al., 2012). Geologic deformation rates along many of the faults in the Reno–Carson City–Lake Tahoe region, which is in the WLB, remain poorly constrained, and urban development has made assessing paleoseismic parameters difficult along many structures. East of WLB, the main tectonic element is Basin and Range extension. Crustal motion in the eastern third of central Nevada is relatively block-like, and characterized by the 1–2 mm/yr westward motion relative to stable North America (Hammond et al., 2011, 2014; Koehler and Wesnousky, 2011). In the Las Vegas region of southern Nevada, deformation is accommodated across a widely distributed series of faults. Many of these faults are poorly characterized, and paleoseismic parameters are currently insufficient to include several mapped faults in the National Seismic Hazard Map. Strain-rate models for the southwestern United States show zones of elevated strain across these structures (Kreemer et al., 2010; 2012). Thus, seismic hazards have the potential to impact any region of the state.
Improvements to future updates to the National Seismic Hazard Map are dependent on developing a better understanding of spatio-temporal patterns of crustal strain accumulation and release (geodesy and geology), better defining fault geometry, predictive models of source characteristics and ground motions (seismology), and better characterizing site response, basin amplification, and basin depths (geophysics), among other issues. To address future research priorities related to these issues, a two-day workshop was convened at the University of Nevada, Reno to discuss technical issues related to earthquake hazards in Nevada and develop a path forward to reduce uncertainties and improve the National Seismic Hazard Map. The workshop builds on the results of previous working group efforts (Briggs and Hammond, 2011).
This report presents a summary of the key issues discussed at the workshop. A formal publication of the workshop results has been submitted for publication in a peer-reviewed journal. The summary presented here is intended to be a resource for guiding future earthquake research in Nevada and will be archived online at the Nevada Bureau of Mines and Geology (NBMG). The workshop provides a model for future working group meetings of earthquake professionals in Nevada in efforts to better characterize seismic hazards in the state.
Supported by the USGS Earthquake Hazards Program (Award #G17AC00406).