The unusual temporal and spatial slip history of the Wassuk Range normal fault, western Nevada (USA): Implications for seismic hazard and Walker Lane deformation

摘要

We document temporal and spatial variations in vertical displacement rate across 6 temporal orders of magnitude to better under stand how the 100-km-long, east-dipping Wassuk Range normal fault system has accommodated strain in the context of the Walker Lane, a tectonically active, NNW-trending zone of dextral and extensional deformation that affects significant portions of western Nevada and eastern California. We combine Be-10 and Al-26 cosmonuclide exposure ages with shallow seismic and gravity data from the buried hanging wall of the Wassuk fault to derive a post-113 ka (10(5) yr time scale) vertical displacement rate of 0.82 +/- 0.16 mm/yr. We also perform large-scale fault scarp analysis to constrain the long-term (>1 Ma; 10(6) yr time scale) displacement rate. Our fault-scarp analysis results imply similar vertical displacement rates, with higher long-term vertical displacement rates along the southern fault (similar to 1.1 mm/yr) relative to the northern fault (<0.8 mm/yr). Vertical displacement rate data at the 106, 105, 103, and 101 yr time scales (this study and others) support a constant vertical displacement rate between 0.75 and 1.0 mm/yr for the Wassuk Range fault since ca. 4 Ma. An anomalously high vertical displacement rate at the 104 yr time scale is best explained by an earthquake cluster between ca. 15.5 ka and ca. 10.5 ka, potentially linked to rapid filling of the Walker Lake basin immediately prior to the ca. 13 ka Sehoo highstand of ancestral Lake Lahontan. We hypothesize that this flood event induced seismicity by placing an additional load on the hanging wall of the Wassuk Range fault and by increasing the pore-fluid pressure within and adjacent to the fault. Although an earthquake cluster like this is consistent with Wallace-type fault behavior, we suggest that a nontectonic stressor induced the cluster, resulting in the apparent discrepancy in vertical displacement rate at the 104 yr time scale. Thus, we posit that the long-term slip along Wassuk fault is better explained by slip-predictable Reid-type behavior, which deviates from the behavior of other well-documented fault systems. Based on these results, we suggest that similar, unrecognized nontectonic stressors may influence rates of strain release along other major fault systems worldwide. Finally, we present a revised model of central Walker Lane kinematics, based on data from this and other recent studies.