Investigating the Causative Mechanisms of Widely Distributed Fracturing Around the 2020 m6.5 Monte Cristo Range Earthquake Rupture, Nevada Usa
Description:
The 15 May 2020 M6.5 Monte Cristo Range, NV earthquake ruptured 30 km of left-lateral and left-normal faults, yet produced surface rupture only along 9 km of oblique left-normal faults, >10 km west of the epicenter. These surface ruptures are complex and distributed, but can be broadly characterized as two subparallel NE-striking fault zones connected by a narrow west-dipping normal fault. Ground deformation imaged by satellite radar interferometry (InSAR) indicates that the southern (and larger) of these two main surface rupture zones lies along the trace of the source fault. However, the distributed nature of the discrete surface breaks precludes identification of a single main surface trace; instead the faulting at the surface comprises a 500 – 800-meter-wide zone of closely spaced cracks (decimeters to decameters apart and meters to tens of meters long) each exhibiting cm-scale left-extensional offsets. Whether pervasive surface cracking like this represents a hazard to the built environment depends upon the strain it reflects, which is dictated by whether it formed through shaking effects, bulk strain of the volume, or discrete fault ruptures breaching the ground surface.
Using field mapping and remote sensing, we evaluate the spatial distribution of different controls on fracture distribution. We find that almost all of the fractures are located in alluvium that experienced shear strains of >10-4 within the continuous deformation field of the rupture. Thus while shaking may play a role in generating some of the fractures, they likely represent the manifestation of tectonic strain in surface materials. We further conclude based on mapping of alluvial landforms that fracture density and distribution is modulated by the age and composition of surface deposits likely reflecting variations in cohesion and yield strength. Excavation could illuminate the depth extent of many of these fractures and help distinguish between generative mechanisms.
Session: Above the Seismogenic Zone: Fault Damage and Healing in the Shallow Crust [Poster]
Type: Poster
Date: 4/19/2023
Presentation Time: 08:00 AM (local time)
Presenting Author: Austin J. Elliott
Student Presenter: No
Invited Presentation:
Authors
Austin Elliott Presenting Author Corresponding Author ajelliott@usgs.gov U.S. Geological Survey |
Alexandra Hatem ahatem@usgs.gov U.S. Geological Survey |
Charles Trexler ctrexler@usgs.gov U.S. Geological Survey |
Richard Koehler rkoehler@unr.edu University of Nevada, Reno |
Seth Dee sdee@unr.edu Nevada Bureau of Mines and Geology |
Ian Pierce ian.pierce@earth.ox.ac.uk University of Oxford |
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Investigating the Causative Mechanisms of Widely Distributed Fracturing Around the 2020 m6.5 Monte Cristo Range Earthquake Rupture, Nevada Usa
Category
Above the Seismogenic Zone: Fault Damage and Healing in the Shallow Crust