Geodetic Observation of Seismic Cycles before, during, and after the 2020 Monte Cristo Range, Nevada Earthquake

The 15 May 2020, M 6.5 Monte Cristo Range, Nevada earthquake (MCE) occurred inside the footprint of the semicontinuous MAGNET and continuous Network of the Americas Global Positioning System (GPS) networks, which provide precise geodetic coverage in the western Great basin. The event occurred in the White Mountain seismic gap between twentieth century events in the eastern central Walker Lane, on an east-northeast extension of faults in the Candelaria Hills. The earthquake precipitated a rapid and sustained GPS field response, which is providing data on the MCE pre-, co-, and postseismic deformation. The response was especially rapid owing to ∼1 dozen MAGNET stations immediately surrounding the epicenter being fortuitously occupied with receivers at event time. Modeling the coseismic displacements suggests that the MCE offset was ∼1  m, greater than the individual observations of surface rupture, but consistent with the seismic moment. Although the epicenter is separated from most of the observed surface rupture by ∼10  km, the slip plane inferred from the GPS data spans the gap, suggesting deep slip continuity that tapered toward the surface, making the event partially blind. However, the range of magnitudes estimated from geologic, geodetic, and seismic data overlap in the range of Mw 6.3–6.4. Postseismic displacement over several months occurred in directions aligned with the coseismic displacement, suggesting afterslip of over 9% of the coseismic displacement, too large to be explained by aftershock seismicity, suggesting that most postseismic deformation was aseismic. The interseismic direction of no-length change was very closely aligned to the MCE slip azimuth, as expected for a strike-slip event. This alignment is sensitive to transient postseismic viscoelastic deformation from previous earthquakes in the western Great basin, which may have temporarily improved the alignment. Thus, these viscoelastic transients may have created conditions favoring the slip to occur on the MCE fault.