Field Response and Surface-Rupture Characteristics of the 2020 M 6.5 Monte Cristo Range Earthquake, Central Walker Lane, Nevada

Abstract

The M 6.5 Monte Cristo Range earthquake that occurred in the central Walker Lane on 15 May 2020 was the largest earthquake in Nevada in 66 yr and resulted in a multidisciplinary scientific field response. The earthquake was the result of left-lateral slip along largely unmapped parts of the Candelaria fault, one of a series of east–northeast-striking faults that comprise the Mina deflection, a major right step in the north–northwest structural grain of the central Walker Lane. We describe the characteristics of the surface rupture and document distinct differences in the style and orientation of fractures produced along the 28 km long rupture zone. Along the western part of the rupture, left-lateral and extensional displacements occurred along northeasterly and north-striking planes that splay off the eastern termination of the mapped Candelaria fault. To the east, extensional and right-lateral displacements occurred along predominantly north-striking planes that project toward well-defined Quaternary and bedrock faults. Although, the largest left-lateral displacement observed was ∼20 cm, the majority of displacements were <5 cm and were distributed across broad zones up to 800 m wide, which are not likely to be preserved in the geologic record. The complex pattern of surface rupture is consistent with a network of faults defined in the shallow subsurface by aftershock seismicity and suggests that slip partitioning between east-striking left-lateral faults and north to northwest-striking right-lateral faults plays an important role in accommodating northwest-directed transtension in the central Walker Lane.

Geodetic Observation and Modeling of the Coseismic and Postseismic Deformations Associated With the 2020 Mw 6.5 Monte Cristo Earthquake

“…Neither fault was previously mapped by geologic, tectonic, or historical seismology field investigations (Wesnousky, 2005). The simultaneous estimation of all the geometric parameters for faults F1 and F2 is difficult because the surface cracks caused by the Monte Cristo earthquake are characterized by a complicated fault network distributed across broad zones (Koehler et al., 2021). Thus, the surface positions and strikes of the two faults were determined independently based on surface interferograms and aftershock distributions.…”

“…The simultaneous estimation of all the geometric parameters for faults F1 and F2 is difficult because the surface cracks caused LI ET AL. (Koehler et al, 2021). Thus, the surface positions and strikes of the two faults were determined independently based on surface interferograms and aftershock distributions.…”

“…The preliminary focal mechanism solutions of the U.S. Geological Survey and Global Centroid Moment Tensor agree that the Monte Cristo earthquake occurred due to a strike‐slip on either an EW or NS‐trending fault (Figure 1a). More than 6,500 aftershocks were recorded by the Nevada Geodetic Laboratory (NGL) within 3 weeks of the mainshock, exhibiting high aftershock productivity similar to that of the 2019 Ridgecrest earthquake sequence that occurred in the northern part of the Eastern California Shear Zone (ECSZ) (Koehler et al., 2021; Li et al., 2020; Liu et al., 2019; Ross et al., 2019). The focal mechanisms of the aftershocks (Mw > 5.0) in the western and eastern segments are characterized by normal and sinistral strike‐slip components, respectively, and show obvious spatial variations along the trend of the aftershock cluster (Figure 1b), implying a complicated source rupture process of the mainshock.…”

The 2020 Monte Cristo (Nevada) Earthquake Sequence: Stress Transfer in the Context of Conjugate Strike‐Slip Faults

“…Aftershock distribution and focal mechanism solutions (Ruhl et al., 2021; Figure 1), surface rupture mapping (Koehler et al., 2021), GPS measurement (Hammond et al., 2021), and surface deformation deduced from Synthetic Aperture Radar Interferogram (InSAR), indicates that the 2020 Monte Cristo event occurred within two distinct zone of seismicity from west to east characterized by a complex pattern of surface rupture between NE‐striking oblique left‐normal faults, with minor slip on north‐striking right‐lateral faults. Seismicity and geodesy show a predominantly E‐W rupture plane with hints of perpendicular intersecting structures.…”

Strain and Velocity Across the Great Basin Derived From 15‐ka Fault Slip Rates: Implications for Continuous Deformation and Seismic Hazard in the Walker Lane, California‐Nevada, USA

“…Finally, the 2020 Monte Cristo, Nevada, earthquake is modern evidence of a moderate earthquake producing oblique slip that may be missed in the paleoseismic record. The M6.5 earthquake reached a peak slip of 0.8 m at 4 km depth and produced only small surface offsets up to ∼20 cm (Koehler et al, 2021;Zheng et al, 2020), with most offsets <5 cm and distributed in zones up to 800 m wide (Koehler et al, 2021). Small offsets are hard to measure in the field, will be quickly eroded on the surface, and may be concealed by displacement from larger earthquakes in a paleoseismic trench.…”