Nevada ranks third in the nation for current seismic activity. Earthquake data bases are available that provide current and historical earthquake information, and these can be accessed to gain information on seismic activity in the vicinity of the proposed High-Level Nuclear Waste Repository site at Yucca Mountain, in southern Nevada. The data bases reviewed for the southern Nevada area were the Council of the National Seismic System Composite Catalogue and the Southern Great Basin Seismic Network.
Analysis of the available data indicates that, since 1976, there have been 621 seismic events of magnitude greater than 2.5 within a 50-mile radius of Yucca Mountain. Reported underground nuclear weapons tests at the Nevada Test Site have been excluded from this count.
The most notable event during this period was a magnitude 5.6 earthquake near Little Skull Mountain, about 8 miles southeast of the Yucca Mountain site, that occurred on June 29, 1992. This earthquake caused damage to a nearby Department of Energy field office building. This earthquake, and many after-shocks, occurred on a fault that had not previously been identified. The Little Skull Mountain earthquake and numerous others at about the same time in the western U.S. are considered to have been triggered by the magnitude 7.4 Landers earthquake, in California.
The only significant cluster of earthquake activity in the 50-mile radius area is in Rock Valley, about 12 miles southeast of Yucca Mountain. The data base also reveals that, in 1948, there was a magnitude 3.6 event on the southeast boundary of the Yucca Mountain site, in an area known to have a number of faults. Recently, there have been other events recorded beneath Yucca Mountain with magnitudes less than 2.5.
Earthquake activity is a safety concern both during operation, above and below ground, and after closure of a repository at Yucca Mountain.
The mountain ranges and valleys of the Basin and Range, including the Yucca Mountain area, are a result of millions of years of intense faulting and volcanism. Records of recent events indicate that faulting is an ongoing process in the vicinity of Yucca Mountain that is expected to continue long into the future. Thirty-three faults are known to exist within and adjacent to the Yucca Mountain site.
The 20-year record reported here is approximately the same period of time that the Department of Energy has been evaluating the Nevada Test Site and Yucca Mountain as a potential high-level nuclear waste disposal site.