Testing the Synchronicity of Splay-Fault Ruptures in Carson Valley, Nevada, United States

Abstract

The Carson City and Indian Hills faults in Carson City, Nevada, splay northeastward from the major range-bounding Genoa fault. Each splay is part of the Carson range fault system that extends nearly 100 km northward from near Markleeville, California, to Reno, Nevada. Stratigraphic and structural relationships exposed in paleoseismic excavations across the two faults yield a record of ground-rupturing earthquakes. The most recent on the Carson City fault occurred around 473–311 B.P., with the two penultimate events between 17.9 and 8.1 ka. Two trench exposures across the Indian Hills fault record the most recent earthquake displacement after ∼900 yr, preceded by a penultimate surface rupture ≥∼10,000, based on radiocarbon and infrared-stimulated luminescence dating of exposed sediments. The age estimates allow that the Carson City and Indian Hills faults ruptured simultaneously with a previously reported large earthquake on the Genoa fault ∼514–448 B.P. Similar synchronicity of rupture is not observed in the record of penultimate events. Penultimate ages of ruptures on the Carson City and Indian Hills faults are several thousand years older than that of the Genoa fault from which they splay. Together, these observations imply a variability in rupture moment through time, demonstrating the importance of considering multi-fault rupture models for seismic hazard analyses.

Spatiotemporal Clustering of Paleoseismicity in the Walker Lane, USA: An Extensional Supercycle?

“…E2 was a smaller event, occurring only on the 8‐km‐long IH fault, from 1,265 to 591 cal ybp. It is possible that E2 is actually E1, as interpreted by the original authors (Pierce, Wesnousky, Saha, & Moon, 2021), but this requires rejecting two radiocarbon ages from fissure deposits and the result does not significantly change the outcome of this study. E3 then occurred on the Washoe Valley and Mt.…”

“…(2011), Wesnousky and Caffee (2011), dePolo (2014), Seitz et al. (2016), and Pierce, Wesnousky, Saha, and Moon (2021). The OxCal formatted inputs are available here: https://doi.org/10.5281/zenodo.6463350.…”

“…This result is consistent with not only topography, where the highest displacements are situated along the steepest sections of rangefront (Figure 1), but also with estimates of vertical slip rates (Figure 3b). The SG fault has a late Pleistocene rate of 0.4-0.6 mm/yr (Rood et al, 2011;Wesnousky et al, 2016), the CG fault has a late Holocene rate of 2-3 mm/yr , the KC fault has a Holocene rate of 1.5-2.0 mm/yr (dePolo, 2014), and the IH and CC faults have Holocene rates of <0.1 and ∼0.4 mm/yr, respectively (Pierce, Wesnousky, Saha, & Moon, 2021) (Figure 3b). At a given location along a fault, I consider the smallest offsets a result of the most recent earthquake, while larger offsets are the cumulative result of multiple events or simply larger displacements (e.g., Haddon et al, 2016;Li et al, 2017).…”

“…Taken together these five events (E1, E2, and E3, plus the IVF and ECV events) provide evidence of a prehistoric earthquake supercycle along the CRFS from ∼800 to 500 cal ybp. The individual recurrence times of each of these faults ranges from three to 30 times the 300‐year duration of this earthquake cluster (e.g., ∼1.2 ka recurrence of the Genoa fault, Ramelli, Bell, et al., 1999, vs. the Carson City and Indian Hills faults recurrences of ∼8 and ∼10 ka, respectively, Pierce, Wesnousky, Saha, & Moon, 2021), suggesting this is a non‐random process, and represents a period of increased seismicity. Other nearby faults did not rupture during this time: the West Tahoe fault last ruptured ∼5 ka (Seitz, 2015), the Polaris fault has ruptured once in the last ∼8 ka (Melody et al., 2012), the Antelope Valley fault ruptured ∼1.3 ka (Sarmiento et al., 2011), and the Smith Valley rangefront fault ruptured ∼3.5 ka (Wesnousky & Caffee, 2011).…”

“…To understand the timing of past events along the CRFS, the event horizons from prior trenching studies along the CRFS and surrounding faults were first collated (dePolo, 2014; dePolo & Sawyer, 2005; Pierce, Wesnousky, Saha, & Moon, 2021; Ramelli & Bell, 2009; Ramelli & dePolo, 1996; Ramelli, Bell, et al., 1999; Ramelli, dePolo, & Bell, 1999; Ramelli et al., 2007; Sarmiento et al., 2011; Seitz et al., 2016; Wesnousky & Caffee, 2011). As these prior studies use a variety of different approaches for reporting and interpreting ages, their results were recalibrated using OxCal (Bronk Ramsey, 1995) to produce stratigraphic models bracketing event windows.…”