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

被引:234
作者
Bennett, RA
Wernicke, BP
Niemi, NA
Friedrich, AM
Davis, JL
机构
[1] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA
[2] Univ Potsdam, Inst Geowissensch, D-14476 Golm, Germany
[3] Univ Calif Santa Barbara, Dept Geol Sci, Santa Barbara, CA 93106 USA
[4] CALTECH, Div Geol & Planetary Sci, Pasadena, CA 91125 USA
关键词
D O I
10.1029/2001TC001355
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
[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 - 117degrees W. We find that the SNGV microplate translates with respect to the CP at a rate of 11.4 +/- 0.3 mm yr(-1) oriented N47 +/- 1 degreesW and with respect to NA at a rate of similar to12.4 mm yr(-1) also oriented N47degreesW, slower than most previous geodetic estimates of SNGV-NA relative motion, and nearly 7degrees counterclockwise from the direction of P-NA relative plate motion. We estimate CGB-CP relative motion of 2.8 +/- 0.2 mm yr(-1) oriented N84 +/- 5 degreesW, 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(-1) 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(-1) oriented N37 +/- 2 degrees 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 N37degreesW directed right lateral shear at rates of ( 1) 57 +/- 9 nstr yr(-1) across a zone of width similar to125 km in the south ( latitude similar to36degreesN), (2) 25 +/- 5 nstr yr(-1) in the central region (latitude similar to38degreesN), and (3) 36 +/- 1 nstr yr(-1) across a zone of width similar to 300 km in the north ( latitude similar to40degreesN). 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(-1) 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(-1) across the northern Basin and Range but implying a distinctly different mechanism of deformation from extension on north trending, range-bounding 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.
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