Anomalous Strain Accumulation in the Yucca Mountain Area, Nevada

Abstract

Global Positioning System (GPS) surveys from 1991 to 1997 near Yucca Mountain, Nevada, indicate west-northwest crustal elongation at a rate of 1.7 +/- 0.3 millimeters per year (1final sigma) over 34 kilometers, or 50 +/- 9 nanostrain per year. Global Positioning System and trilateration surveys from 1983 to 1997 on a 14-kilometer baseline across the proposed repository site for high-level radioactive waste indicate that the crust extended by 0.7 to 0.9 +/- 0.2 millimeter per year (50 to 64 +/- 14 nanostrain per year), depending on the coseismic effect of the Ms 5.4 1992 Little Skull Mountain earthquake. These strain rates are at least an order of magnitude higher than would be predicted from the Quaternary volcanic and tectonic history of the area.

Characterize Framework for Igneous Activity at Yucca Mountain, Nevada

“…(CRWMS M&O 1998 [DIRS 105347], Chapter 4, p. 4-12). This million-year record of low-volume volcanism is inconsistent with the hypothesis that approximate 100,000 year time intervals within this period have involved particularly high strain rates that would lead to an order-of-magnitude increase in magmatic activity, as stated by Wernicke et al (1998[DIRS 103485], p. 2099 Savage et al (1998 [DIRS 145359], p. 1007b) calculated that an order-of-magnitude increase in the volcano recurrence rate would result in a 90 percent probability of a new volcano forming between 80 ka and the present. No such event has occurred.…”

Characterize Framework for Igneous Activity at Yucca Mountain, Nevada

“…GRWMS M&O 1998 [105347], Chapter4, p. 4-12). This milliorryear record of lowvolume volcanism is inconsistent with the hypothesis that approximate 100,000 year time intervals within this period have involved particularly high strain rates that would lead to an order-of-magnitude increase in magmatic activity, as stated by Wernicke et al (1998Wernicke et al ( [ 1034851, p. 2099 Savage et al (1998 [145359], Figure 1) also presented fault displacement data showing that deformation rates in the YMR have decreased since about 60 k.y. ago, suggesting that the region is not currently within a period of anomalous strain rate that would couple to increased volcano recurrence rate.…”

Site Characterization Progress Report No.20

“…These data, along with data from previous surveys in 1983, 1984, and 1993, indicate principal strain accumulation rates of ,I = 9+12 nanostraidyr N88"Wkll" and ,2 = -17rt12 nanostraidyr N02"E+11° (extension reckoned positive) (Savage et al 1998). This analysis shows a N65"W extension rate of 5+12 nanostraidyr, significantly less than the 5039 nanostraidyr reported by Wernicke et al (1998) for this area based on data from 1991 to 1997. When strain accumulation on the Death Valley-Furnace Creek and Hunter Mountain-Panamint Valley faults to the west are considered, the residual strain rate in the vicinity of Yucca Mountain is not significant at the 95 percent confidence level (Savage et al 1998).…”

“…Results of a 1998 resurvey of a geodetic array centered on the site, along with data from earlier surveys, indicate the residual strain rate at Yucca Mountain is significantly less than that calculated by Wernicke et al (1998) and is not significant (Savage et al 1998). …”