Contemporary strain rates in the northern Basin and Range province from GPS data

Abstract

[1] We investigate the distribution of active deformation in the northern Basin and Range province using data from continuous GPS (CGPS) networks, supplemented by additional campaign data from the Death Valley, northern Basin and Range, and Sierra Nevada-Great Valley regions. To understand the contemporary strain rate field in the context of the greater Pacific (P)-North America (NA) plate boundary zone, we use GPS velocities to estimate the average relative motions of the Colorado Plateau (CP), the Sierra Nevada-Great Valley (SNGV) microplate, and a narrow north-south elongate region in the central Great Basin (CGB) occupying the longitude band 114-117°W. We find that the SNGV microplate translates with respect to the CP at a rate of 11.4 ± 0.3 mm yr À1 oriented N47 ± 1°W and with respect to NA at a rate of $12.4 mm yr À1 also oriented N47°W, slower than most previous geodetic estimates of SNGV-NA relative motion, and nearly 7°counterclockwise from the direction of P-NA relative plate motion. We estimate CGB-CP relative motion of 2.8 ± 0.2 mm yr À1 oriented N84 ± 5°W, consistent with roughly east-west extension within the eastern Great Basin (EGB). Velocity estimates from the EGB reveal diffuse extension across this region, with more rapid extension of 20 ± 1 nstr yr À1 concentrated in the eastern half of the region, which includes the Wasatch fault zone. We estimate SNGV-CGB relative motion of 9.3 ± 0.2 mm yr À1 oriented N37 ± 2°W, essentially parallel to P-NA relative plate motion. This rate is significantly slower than most previous geodetic estimates of deformation across the western Great Basin (WGB) but is generally consistent with paleoseismological inferences. The WGB region accommodates N37°W directed right lateral shear at rates of (1) 57 ± 9 nstr yr À1 across a zone of width $125 km in the south (latitude $36°N), (2) 25 ± 5 nstr yr À1 in the central region (latitude $38°N), and (3) 36 ± 1 nstr yr À1 across a zone of width $300 km in the north (latitude $40°N). By construction there is no net extension or shortening perpendicular to SNGV-CGB relative motion. However, we observe about 8.6 ± 0.5 nstr yr À1 extension on average in the direction of shear from southeast to northwest within the Walker Lane belt, comparable to the average east-west extension rate of 10 ± 1 nstr yr À1 across the northern Basin and Range but implying a distinctly different mechanism of deformation from extension on north trending, rangebounding normal faults. An alternative model for this shear parallel deformation, in which extension is accommodated across a narrow, more rapidly extending zone that coincides with the central Nevada seismic belt, fits the WGB data slightly better. Local anomalies with respect to this simple kinematic model may reveal second-order deformation signals related to more local crustal dynamic phenomena, but significant improvements in velocity field resolution will be necessary to reveal this second-order pattern.

The time scales of continental rifting: Implications for global processes

“…At the longest time scales, variations in the direction of the least principal stress direction, which forms and loads faults, result in slow opening with minimal magmatism, as is seen in the Rio Grande rift. During periods of stable plate confi gurations, over time periods of millions of years, rates match well with extrapolations of modern plate opening (e.g., Vigny et al, 2006;McClusky et al, 2010;Bennett et al, 2003). Observations from the Baikal rift and Rio Grande rift suggest that episodes of stress fi eld rotation on geologic time scales appear to coincide with tectonic quiescence of continental rifts.…”

Detecting Large-scale Intracontinental Slow-slip Events (SSEs) Using Geodograms

“…Previous analyses of this network (Bennett et al 2002;Davis et al 2006;Wernicke et al 2008) show that average horizontal velocities (relative to a North American reference frame) rise from near zero on the eastern side of the network to about 3 mm/yr oriented due west near the Nevada-Utah border, indicating crustal extension in the eastern Basin and Range (Figure 1). Average velocities remain relatively constant across eastern Nevada, progressively rotating northwestward and increasing in magnitude up to 12 mm/ yr across western Nevada, accommodating both extension and right-lateral shear associated with the Pacific-North America transform plate boundary to the west (e.g., Bennett et al 2003;Hammond and Thatcher 2004). Position time series over the entire decade of data indicate significant secular changes in velocity (Davis et al 2006), such as in the east component of motion for site EGAN (Figure 2A).…”

Acceleration and evolution of faults: An example from the Hunter Mountain–Panamint Valley fault zone, Eastern California

“…The Eastern California Shear Zone (ECSZ) represents a zone of significant right lateral shear in western North America, accommodating ~20-25% of Pacific-North America motion (Lee et al, 2009;Dokka and Travis, 1990a;Dokka and Travis, 1990b;Savage et al, 1990;Sauber et al, 1994;Dixon et al, 2000;Miller et al, 2001;Bennett et al, 2003;Frankel et al, 2007) (Figure 1). Most of the remaining motion is accommodated by the San Andreas Fault.…”