The 2020 Mw 6.5 Monte Cristro Range (Nevada) earthquake: anatomy of a
large rupture through a region of highly-distributed faulting
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
Author ProfileAbstract
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.