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Group A, Poster #045, Seismology

A remarkable sequence in a remote location: A detailed characterization of the 2014-2018 Sheldon, Nevada earthquake swarm

Daniel Trugman, William H. Savran, Christine J. Ruhl, & Ken Smith
Poster Image: 

Poster Presentation

2023 SCEC Annual Meeting, Poster #045, SCEC Contribution #13005 VIEW PDF
In July of 2014, a prolific earthquake swarm initiated within the Sheldon Wildlife Refuge in the remote northwest corner of Nevada, a region of low background seismicity rate. Over the next three years, the sequence produced 26 M4 earthquakes and more than 250 M3s, with no clear mainshock or obvious driving force. We combine a suite of complementary seismological techniques to characterize in detail this unusual earthquake sequence. High-precision relocations reveal an east-dipping normal fault as the dominant structure that intersects with a secondary, subvertical cross fault. Seismicity occurs in bursts of activity with complex migration patterns along these two structures before eventuall...y transitioning to downdip to the east. Inversion of hundreds of moment tensors constrain the overall normal faulting stress regime. Source spectral analysis suggests that the stress drops and rupture properties of these normal faulting events are typical for tectonic earthquakes in the western US. While station coverage is sparse in this remote study region, the timely installation of a temporary seismometer allows us to detect nearly 70,000 earthquakes over a 40-month time period when the seismic activity is highest. Systematic measurements of earthquake sequence productivity in California and Nevada demonstrate that the Sheldon sequence is without precedent over the past 40 years of monitoring, and is difficult to reconcile with current understanding of crustal deformation in the region. We posit that the dynamics of the swarm are likely facilitated by feedback and interactions between local hydrothermal processes and earthquake triggering at the transition zone between subparallel fault systems.