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On 15 May 2020 an Mww 6.5 earthquake occurred beneath the Monte Cristo Range in the Mina Deflection region of western Nevada. Rapid deployment of eight temporary seismic stations enabled detailed analysis of its productive and slowly decaying aftershock sequence (p=0.8), which included ∼18,000 autodetected events in 3.5 months. Double-difference, waveform-based relative relocation of 16,714 earthquakes reveals a complex network of faults, many of which cross the inferred 35-km-long east–northeast-striking, left-lateral mainshock rupture. Seismicity aligns with left-lateral, right-lateral, and normal mechanism moment tensors of 128 of the largest earthquakes. The mainshock occurred near the middle of the aftershock zone at the intersection of two distinct zones of seismicity. In the western section, numerous subparallel, shallow, north-northeast-striking faults form a broad flower-structure-like fault mesh that coalesces at depth into a near-vertical, left-lateral fault. We infer the near-vertical fault to be a region of significant slip in the mainshock and an eastward extension of the left-lateral Candelaria fault. Near the mainshock hypocenter, seismicity occurs on a northeast-striking, west-dipping structure that extends north from the eastern Columbus Salt Marsh normal fault. Together, these two intersecting structures bound the Columbus Salt Marsh tectonic basin. East of this intersection and the mainshock hypocenter, seismicity occurs in a narrow, near-vertical, east-northeast-striking fault zone through to its eastern terminus. At the eastern end, the aftershock zone broadens and extends northwest toward the southern extension of the northwest-striking, right-lateral Petrified Springs fault system. The eastern section hosts significantly fewer aftershocks than the western section, but has more moment release. We infer that shallow aftershocks throughout the system highlight fault-fracture meshes that connect mapped fault systems at depth. Comparing earthquake data with surface ruptures and a simple geodetic fault model sheds light on the complexity of this recent M 6.5 Walker Lane earthquake.

The Nevada Seismological Laboratory (NSL) at the University of Nevada, Reno, installed eight temporary seismic stations following the 15 May 2020 Mww 6.5 Monte Cristo Range earthquake. The mainshock and resulting aftershock sequence occurred in an unpopulated and sparsely instrumented region of the Mina deflection in the central Walker Lane, approximately 55 km west of Tonopah, Nevada. The temporary stations supplement NSL’s permanent seismic network, providing azimuthal coverage and near-field recording of the aftershock sequence beginning 1–3 days after the mainshock. We expect the deployment to remain in the field until May 2021. NSL initially attempted to acquire the Monte Cristo Range deployment data in real time via cellular telemetry; however, unreliable cellular coverage forced NSL to convert to microwave telemetry within the first week of the sequence to achieve continuous real-time acquisition. Through 31 August 2020, the temporary deployment has captured near-field records of three aftershocks ML≥5 and 25 ML 4–4.9 events. Here, we present details regarding the Monte Cristo Range deployment, instrumentation, and waveform availability. We combine this information with waveform availability and data access details from NSL’s permanent seismic network and partner regional seismic networks to create a comprehensive summary of Monte Cristo Range sequence data. NSL’s Monte Cristo Range temporary and permanent station waveform data are available in near-real time via the Incorporated Research Institutions for Seismology Data Management Center. Derived earthquake products, including NSL’s earthquake catalog and phase picks, are available via the Advanced National Seismic System Comprehensive Earthquake Catalog. The temporary deployment improved catalog completeness and location quality for the Monte Cristo Range sequence. We expect these data to be useful for continued study of the Monte Cristo Range sequence and constraining crustal and seismogenic properties of the Mina deflection and central Walker Lane.

The Pacific coast of the contiguous United States hosts the highest seismic risk in the country due to the intersection of high-seismic hazard and the high densities of population and infrastructure. The regional seismic networks in Washington, Oregon, Nevada, and California have operated for many years and have collected long catalogs and large amounts of seismic waveform data in a variety of formats, including digital records. These data are available for engineering purposes and research into earthquakes, other natural and man-made seismic sources, and the Earth’s structure. The West Coast networks are closely coordinating as they embark on the implementation of West Coast ShakeAlert, an earthquake early warning system.

The Wassuk Range fault zone is an 80‐km‐long, east‐dipping, high‐angle normal fault that flanks the eastern margin of the Wassuk Range in central Nevada. Observations from two alluvial fan systems truncated by the fault yield information on the vertical slip rate and Holocene earthquake history along the range front. At the apex of the Rose Creek alluvial fan, radiocarbon dating of offset stratigraphy exposed in two fault trenches shows that multiple earthquakes resulted in 7.0 m of vertical offset along the fault since ∼9400 cal B.P. These data yield a Holocene vertical slip rate of 0.7±0.1 mm/yr. The south trench exposure records at least two faulting events since ∼9400 cal B.P., with the most recent displacement postdating ∼2810 cal B.P. The north trench exposure records an ∼1 m offset between ∼610 cal B.P. and A.D. ∼1850, a 1.3‐m minimum offset prior to ∼1460 cal B.P., and one earlier undated earthquake of a similar size. Variations in stratigraphy and limited datable material preclude a unique correlation of paleoevents between the two trenches. Approximately 25 km north, the range‐front fault has truncated and uplifted a remnant of the Penrod Canyon fan by >40 m since the surface was deposited ∼113 ka, based on cosmogenic dating of two large boulders. These data allow an estimate of the minimum late Pleistocene vertical slip rate at >0.3–0.4 mm/yr for the Wassuk Range fault zone. Online Material: Tables summarizing radiocarbon and cosmogenic analyses, photos of rocks sampled for cosmogenic analyses, and figures summarizing cosmogenic exposure age estimates.

Offset Quaternary deposits, measurements of fault scarps, and the excavation of two trenches along the eastern Sierra Nevada range front provide information on the rate and style of active faulting in Antelope Valley, California, and Reno, Nevada. Structural, stratigraphic, and pedogenic relations exposed in a trench in Antelope Valley (![Graphic][1] latitude) record two Holocene surface-rupturing earthquakes. Radiocarbon dates place the most recent and penultimate events at about 1350 calibrated years before present (cal B.P.) and older than about 6250 cal B.P., respectively. An approximate fault-slip rate of ∼0.7 mm/yr is calculated by dividing the 3.6-m offset that occurred in the most recent event by the time between the two radiocarbon ages (∼5000 years). A second trench excavated across the Carson Range frontal fault in Reno, Nevada (![Graphic][2] latitude) revealed a sharp, planar, low-angle failure surface dipping 33° E, lending to the possibility that the active normal fault is characterized by a dip much lower than expected from standard frictional considerations. [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif