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Left-lateral Faulting Beneath the Monte Cristo Range, West-central Nevada

Description: 

Earthquakes of M6.5 or smaller are challenging to interpret in the geomorphic record because of subdued coseismic surface rupture that can be obscured through time. We investigated one such earthquake, the 15 May 2020 M6.5 Monte Cristo Range (MCR) earthquake of west-central Nevada, a left-lateral rupture. Small coseismic surface breaks with horizontal displacement <20 cm were documented west of the MCR immediately following the earthquake. The eastern portion of the rupture, where the earthquake nucleated within the MCR, had no documented surface rupture. We further investigated the apparent lack of pre-existing or coseismic faulting through the MCR using additional field reconnaissance mapping, lidar review, and optical pixel tracking. None of these investigations revealed apparent surface faulting through the MCR in the eastern rupture domain, despite InSAR and aftershock observations indicating that an east-west trending, left-lateral fault ruptured at depth. While optical pixel tracking revealed a broad fault zone across the eastern portion of the rupture, this method showed a ~5km long surface rupture co-located with field observed surface rupture in the western domain. These surface rupture features have appreciably degraded over the four years since the earthquake. We completed two return trips to the rupture area to document the evolution of 2020 rupture features. Sites with vertical displacement (<10 cm) were better preserved than sites with primarily horizontal displacement. Taken together, our observations highlight the limited preservation of a moderate magnitude strike-slip earthquake, similar to observations made following the 1968 M6.6 Borrego Mountain earthquake. In probabilistic seismic hazard analyses, an event like this is unlikely to be captured in a geologic compilation of fault geometries (in the eastern domain) or with a geologic slip rate due to a lack of consistent long-term preservation of displacement along strike (in the western domain). Rather, this rupture represents a classic ‘background’ earthquake and would be captured by gridded seismicity.

Session: The Landscape Record of Earthquakes and Faulting [Poster]

Type: Poster

Date: 4/16/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Alexandra

Student Presenter: No

Invited Presentation: 

Poster Number: 6

Authors