SURFACE RUPTURE FROM THE 2020 M6.5 MONTE CRISTO RANGE EARTHQUAKE, NEVADA

The May 15, 2020 M6.5 Monte Cristo Range earthquake was the largest in NV in 66 years, and produced surface rupture broadly distributed across a ~24 km-long ENE-trending zone. The earthquake occurred in the Mina Deflection, a series of roughly E-W-striking left-lateral faults that connect sets of NW-striking right-lateral faults in the Walker Lane. Surface rupture mapping began in the week following the event using handheld GPS devices, and later refined on post-event, low altitude imagery along sections of the main rupture. The rupture is broadly characterized by two distinct domains roughly separated by Hwy 95: ENE-trending ruptures with the largest measured displacements in the western domain, and an area of distributed N to NNE trending fractures with minor local displacement in the eastern domain. The ruptures are largely in mid-Pleistocene to late Holocene aged surficial deposits. The western domain is characterized by two sub-parallel strands each with up to 10 km of nearly continuous rupture projecting east from the eastern terminus of the mapped Candelaria fault. Left-lateral displacement, up to 20 cm, occurred on ENE-striking strands (~050-070°), and extensional displacement, up to 7 cm vertical, on NNE- striking strands (~010°). The main left-lateral strands exhibit right-stepping traces, moletracks, offset channels, and are commonly adjacent to broad zones (up to 500 m wide) of distributed fracturing. The eastern domain is characterized by N to NNE-striking fracture zones (~350-030°) up to ~1.5 km in length. Displacement up to 5 cm vertical was measured along one rupture, but the zone is largely characterized by cm-scale dilational fractures. The mainshock epicenter, which has an ENE oriented left-lateral focal plane, is located in the eastern domain over 11 km east of the closest measurable left-lateral displacement.

Most ruptures are in locations that do not exhibit evidence of previous displacement, but locally they occur along tectonic geomorphic features consistent with prior faulting including scarps, abrupt range fronts, and pop-up ridges that were not previously mapped. The two domains of distinct rupture orientation mimic the overall fault pattern in the region with ruptures occurring along the projected traces of the active Candelaria, Benton Springs, and E Columbus Salt Marsh faults.