Poster #057, Seismology

The 2020 M6.5 Monte Cristo Range, NV Earthquake and Aftershock Sequence

Emily Morton, Christine J. Ruhl, Ken Smith, Jayne M. Bormann, Rachel L. Hatch, & Gene A. Ichinose
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Poster Presentation

2020 SCEC Annual Meeting, Poster #057, SCEC Contribution #10588 VIEW PDF
The M6.5 Monte Cristo Range (MCR) earthquake occurred on 15 May 2020 at 11:03:27.176 UTC, in an uninhabited region approximately 50 km WNW of Tonopah, NV, within the Mina Deflection structural domain of the Central Walker Lane. No apparent foreshocks were observed; however, the April 2020 M5.2 Mono Lake sequence notably preceded the MCR sequence on the western end of Mina Deflection. The MCR aftershock zone shows a ~35-km-long left-lateral rupture on an ENE striking plane that extends east from the mapped trace of the Candelaria Hills fault. An ~6-km-long NNW striking secondary aftershock zone exists at the east end of the main zone, aligned with an unnamed fault southwest of the Pilot Mount...ains. Both aftershocks zones strike similarly to the moment tensor nodal planes.

The MCR earthquake is the largest to occur in NV since the Dec. 1954 Fairview Peak M7.2 and Dixie Valley M6.8 earthquakes, and the largest in the Walker Lane/Eastern CA Shear Zone since the 2019 M7.1 Ridgecrest earthquake. The MCR earthquake occurred ~195 km NE of the 2019 M7.1 Ridgecrest, 125 km E of the 1993 M6.1 Eureka Valley and 85 km NE of the Mw 6.3 Chalfant, California Walker Lane earthquakes. It was felt as far away as the San Francisco Bay area, CA (~410 km), Salt Lake City, UT (~600 km), and Portland, OR (~890 km).
We present analysis of correlation-based relocations of MCR aftershocks and corresponding moment tensors to isolate the mainshock, fault orientations, and overall sequence behavior. Eight temporary broadband and strong motions stations were operating within days of the earthquake, and over the period of 15 May – 31 July 2020, 15,548 aftershocks have been detected with a median depth of 4.4 km. There are 42 aftershocks ML 4 or larger and 4 aftershocks ML 5 or larger. Moment tensors of 129 aftershocks ML>3 indicate a cumulative aftershock Mw of 5.35. The aftershock distribution extends bilaterally from the mainshock and does not show temporal migration. Aftershocks are largely strike slip events (84%) with some normal faulting events (16%). Magnitude completeness during this time period is currently ML 2.17 for analyst-reviewed aftershocks and ML 1.07 for reviewed and automatically located aftershocks, both with a b-value of 0.83. There appears to be a gap in aftershocks where the aftershock zone crosses the region between the southern Benton Springs fault and the northern Eastern Columbus Salt Marsh fault, evident in both analyst-reviewed locations and relocations.