Spatial and temporal constancy of seismic strain release along an evolving segment of the Pacific–North America plate boundary

Abstract

Three new slip rates from the Death Valley–Fish Lake Valley (DVFLV) fault contribute to an exceptionally detailed record of lateral rate variations on this 300-km-long system. From south to north, these three new sites are: South Mud Canyon, Cucomongo Canyon, and Indian Creek. Slip rates were determined by combining offsets measured with 1-m-resolution airborne lidar data with 10Be cosmogenic nuclide surface exposure and optically stimulated luminescence ages from displaced alluvial fans. The offset fans date to 17.4 ± 2.3 ka at South Mud Canyon, 39 ± 3 ka at Cucomongo Canyon, and 6.3 ± 1.8 ka at Indian Creek, yielding slip rates of 2.1 + 0.5/−0.4 mm/yr, 6.1 + 1.3/−1.0 mm/yr and 2.2 + 0.8/−0.6 mm/yr, respectively. At Indian Creek, the Holocene (~ 6 ka) and late Quaternary (~ 70 ka) slip rates are the same, within uncertainty, suggesting temporal constancy of seismic strain release along the northern DVFLV fault zone over these time spans. When combined with slip rates determined in earlier companion studies, these results show that the late Quaternary slip rate decreases northward and southward from the central part of the fault, as slip is transferred onto north-trending zones of distributed normal faulting towards the northeast and southwest of the central zone of rapid deformation. This complex pattern of strain accommodation may reflect structural evolution towards a straighter, structurally simpler zone of dextral shear that locally utilizes well-established dextral faults that are linked where necessary by nascent zones of deformation. Summation of the rates of all major faults in the eastern California shear zone (ECSZ) at the 37°N latitude of Red Wall Canyon in northern Death Valley shows that the cumulative geologic rate of ~ 8.5–10 mm/yr is indistinguishable from the ~ 9 mm/yr geodetic rate. Although the cumulative rate on the major faults of the ECSZ is slower to the north and south, this probably reflects more distributed deformation in these areas, rather than transient strain accumulation. These results demonstrate the importance of obtaining multiple slip rates to effectively document the behavior of any fault system, especially in studies of seismic hazard assessment and comparisons of geologic and geodetic rate data.