STRAIN ACCUMULATION ACROSS THE CENTRAL NEVADA SEISMIC ZONE, 1973-1994

Five trilateration networks extending for 280 km along the central Nevada seismic zone (1915 Pleasant Valley, M = 7.3; 1954 Dixie Valley, M = 6.8; 1954 Stillwater, M = 6.8; 1954 Rainbow Mountain, M = 6.6; 1954 Fairview Peak, M = 7.1; and 1932 Cedar Mountain, M = 7.2) have been surveyed 8 times since 1973 to determine deformation along the zone. Within the precision of measurement the deformation appears uniform along the zone and is described by the principal strain rates 0.036 +/- 0.008 mu strain/yr N60 degrees W +/- 3 degrees and -0.031 +/- 0.008 mu strain/yr N30 degrees E +/- 3 degrees, extension reckoned positive. The observed strain rates are consistent with simple, right-lateral, teaser shear at the rate of 0.033 mu strain/yr across a shear zone striking N15 degrees W. This central Nevada shear zone appears to be the northward continuation of the eastern California shear zone. The orientation of the strike-slip and normal-slip ruptures within the central Nevada seismic zone are consistent with principal stress axes parallel to the measured principal strain rate axes. Space-based geodetic measurements (very long baseline interferometry) indicate that the relative motion accommodated across the Basin and Range province west of fly, Nevada, is about 9.1+/-1.5 mm/yr N16 degrees W +/- 8 degrees (Dixon et al., 1995.) Notice that the right-lateral shear zone postulated to explain deformation in the central Nevada seismic zone is properly oriented to accommodate that relative motion. Howsoever, a 135-km effective width of the shear zone would be required to accommodate all of the 9.1 mm/yr relative motion st the strain rates observed in the Nevada seismic zone; only about 3 mm/yr of that relative motion is accommodated within the span of the trilateration networks.