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Complex Rupture and Source Model of the 15 May 2020 Mw 6.5 Monte Cristo Range Earthquake From Insar and Earthquake Relocation

The 15 May 2020 M_w 6.5 Monte Cristo Range earthquake in Nevada, USA occurred in the Mina Deflection (central Walker Lane) along previously-unmapped faults to the east of the Candelaria fault zone. We use Interferometric Synthetic Aperture Radar (InSAR) to characterize the mainshock deformation and model the causative faulting. Three 6-day interferograms, generated from radar images from the Sentinel-1B satellite, reveal phase patterns that suggest the earthquake ruptured along an ENE-striking fault zone. The interferograms are inverted to model the fault geometry in an elastic half space using, first, a uniform slip assumption, and subsequently, distributed slip. Results show that three modeled faults yield the lowest misfit between data and model interferograms, that there is at least ~0.8 m of slip at depth on two of the modeled faults, and that the maximum slip in the top 2 km of the crust is less than ~0.2 m. Each fault has a length of ~10 km, with a total rupture length of at least ~30 km. The westernmost fault trends NE-SW and has a large extensional component (rake ~-47°), while the middle and easternmost faults trend ENE-WSW and have dominant left-lateral motions. We also relocate 155 events of this earthquake sequence to observe the seismicity distribution and source parameters. The calibrated relocation, which minimizes bias from unknown Earth structure, of the mainshock indicate that it initiated at 11.0 km depth, and aftershocks fall within the depth range of 1.0-10.4 km. These focal depths are in good agreement with the InSAR distributed slip model where most of the slip occurred above 12 km depth. The relocated events also illustrate clustering in two main areas—around the NE-SW and the ENE-WSW modeled faults. Both geodesy and seismology results suggest that the earthquake sequence occurred along a segmented, geometrically complex fault zone. Observations in this study help understand the kinematics and distribution of faulting within the Mina Deflection region.

Presenting Author: Israporn Sethanant

Student Presenter: Yes

Day: 4/20/2021

Time: 5:30 PM - 6:45 PM Pacific

Additional Authors