Abstract
We use new and existing data to compile a record of ∼18 latest Quaternary large-magnitude surface-rupturing earthquakes on 7 fault zones in the northwestern Basin and Range Province of northwestern Nevada and northeastern California. The most recent earthquake on all faults postdates the ca. 18–15 ka last glacial highstand of pluvial Lake Lahontan and other pluvial lakes in the region. These lacustrine data provide a window in which we calculate latest Quaternary vertical slip rates and compare them with rates of modern deformation in a global positioning system (GPS) transect spanning the region. Average vertical slip rates on these fault zones range from 0.1 to 0.8 mm/yr and total ∼2 mm/yr across a 265-km-wide transect from near Paradise Valley, Nevada, to the Warner Mountains in California. We converted vertical slip rates to horizontal extension rates using fault dips of 30°–60°, and then compared the extension rates to GPS-derived rates of modern (last 7–9 yr) deformation. Our preferred fault dip values (45°–55°) yield estimated long-term extension rates (1.3–1.9 mm/yr) that underestimate our modern rate (2.4 mm/yr) by ∼21%–46%. The most likely sources of this underestimate are geologically unrecognizable deformation from moderate-sized earthquakes and unaccounted-for coseismic off-fault deformation from large surface-rupturing earthquakes. However, fault dip values of ≤40° yield long-term rates comparable to or greater than modern rates, so an alternative explanation is that fault dips are closer to 40° than our preferred values. We speculate that the large component of right-lateral shear apparent in the GPS signal is partitioned on faults with primary strike-slip displacement, such as the Long Valley fault zone, and as not easily detected oblique slip on favorably oriented normal faults in the region.
Highlights
The Basin and Range Province is a large region of extensional tectonics in the intermountain region of western North America
We found no obvious evidence of reworking of these scarps by lacustrine shoreline processes, which leads us to infer that the timing of the earthquake responsible for the Long Valley fault zone (LVFZ) scarps postdates the age of the last major transgression (Younger Dryas–Gilbert) during which the level of Lake Lahontan rose ~60 m in the time period 13–11 ka (Fig. 5)
We use the size of surface ruptures and this latest Quaternary time window to estimate vertical slip rates on these fault zones and compared them to global positioning system (GPS)-derived rates of modern extension across the region
Summary
20%–25% of the ~50 mm/yr of right-lateral deformation across the plate boundary is distributed east of the Sierra Nevada, and most of that deformation is taken up by strike-slip faulting in the Walker Lane and normal faulting along the eastern and western margins of the province (Dixon et al, 1995; Bennett et al, 1998, 2003; DeMets and Dixon, 1999; Thatcher et al, 1999; Thatcher, 2003; Hammond and Thatcher, 2004; Bormann et al, 2016). The latest phase of extension in the NWBR is thought to have initiated later (≤12 Ma versus ≤30 Ma) and accumulated less strain (≤20% versus 50%–100% extension) than the central part of the province (Colgan et al, 2006b; Lerch et al, 2008; Egger and Miller, 2011). The deposition of extensive middle Miocene volcanic rocks largely predates the onset of the latest phase of extension (Colgan et al, 2004, 2006a, 2006b) in the NWBR
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