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The 2020 Mw 6.5 Monte Cristro Range (Nevada) earthquake: anatomy of a large rupture through a region of highly-distributed faulting
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  • Israporn Sethanant,
  • Edwin Nissen,
  • Léa Pousse‐Beltran,
  • Eric A Bergman,
  • Ian Pierce
Israporn Sethanant
University of Victoria

Corresponding Author:[email protected]

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Edwin Nissen
University of Victoria
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Léa Pousse‐Beltran
School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada- Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, UGE, ISTerre, 38000 Grenoble, France
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Eric A Bergman
Global Seismological Services
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Ian Pierce
University of Oxford
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The 15 May 2020 Mw 6.5 Monte Cristo Range earthquake (MCRE) in Nevada, USA is the largest instrumental event in the Mina deflection, an E-trending stepover zone of highly diffuse faulting within the Walker Lane. The MCRE mostly ruptured previously unmapped faults, motivating us to characterize the behaviour of an earthquake on a structurally-immature fault. We use Interferometric Synthetic Aperture Radar (InSAR) data and regional GNSS offsets to model the causative faulting. Our three fault model indicates almost pure left-lateral motion in the east and normal-sinistral slip in the west. Maximum slip of 1.1 m occurs at 8-10 km depth but less than 0.2 m of slip reaches the surface, yielding a pronounced shallow slip deficit (SSD) of 86%. Our calibrated relocated hypocenters and focal mechanisms indicate that the mainshock initiated at 9 km depth and aftershock focal depths range from 1 to 11 km, helping constrain the local seismogenic thickness. We further present new field observations of fracturing and pebble-clearing that shed light on the western MCRE kinematics, revealing a paired fault system below the spatial resolution of the InSAR model. The segmented fault geometry, off-fault aftershocks with variable mechanisms, distributed surface fractures, limited long-term geomorphic features, and an estimated cumulative offset of 600-700 m, are all characteristic of a structurally-immature fault system. However, the large SSD is not unusual for an earthquake of this magnitude, and a larger compilation of InSAR models (twenty-eight Mw≥6.4 strike-slip events) shows that SSDs are not correlated with structural maturity as previously suggested.