Characterizing Earthquake-triggered Sedimentation in an Intraplate Setting: Delta Collapse and Turbidite Deposition From the 2020 Mw 6.5 Stanley Earthquake (Idaho, USA)
Description:
The 2020 moment magnitude (MW) 6.5 Stanley earthquake generated Modified Mercalli Intensity VI–VII shaking at Stanley Lake, a proglacial basin ~20 km southeast of the epicenter in the Sawtooth Range of central Idaho. Strong shaking triggered the collapse of a ~0.015 km2 delta into Stanley Lake, creating an opportunity to study how lacustrine systems in intraplate tectonic settings respond to and preserve evidence of strong ground motion. In 2025, we conducted a single-beam bathymetric survey and extracted 20 short (0.6–2.0-m-long) percussion-driven gravity cores along three longitudinal transects spanning the delta failure zone, lake depocenter, and moraine-bound eastern margin. Our objectives were to (1) characterize the extent, thickness, texture, and composition of the 2020 earthquake deposit; (2) compare seismically triggered, background, and deltaic sedimentation; and (3) explore evidence of strong ground motion at Stanley Lake from prehistoric earthquakes on nearby faults such as the Sawtooth fault. Our sonar survey reveals rough bathymetry extending from the delta failure zone into a 0.5-km-long, 0.4-km-wide, and ~26-m-deep depocenter. Sediment cores include a near-surface turbidite that is intercalated with laminated background sediments and varies from ~0.5 m to a few millimeters thick in the center of the basin, as well as older coarse beds and tephra deposits. Ongoing analyses using core imaging, particle-size analysis, X-ray fluorescence, and radiocarbon and luminescence dating will characterize the physical and geochemical signatures of the earthquake deposit and the history of basin sediments. Our results will advance our understanding of how earthquake-triggered sediment failures and resulting turbidity flows vary spatially within intraplate lake basins and whether sedimentologic and geochemical proxies can help distinguish seismic from non-seismic deposits in paleoseismic reconstructions.
Session: Subaqueous Evidence for Earthquakes, Coseismic Landslides, Tsunamis and other Cascading Hazards [Poster]
Type: Poster
Date: 4/15/2026
Presentation Time: 08:00 AM (local time)
Presenting Author: Christopher B. DuRoss
Student Presenter: No
Invited Presentation:
Poster Number: 159
Authors
Christopher DuRoss Presenting Author Corresponding Author cduross@usgs.gov U.S. Geological Survey |
Sylvia Nicovich snicovich@usgs.gov U.S. Geological Survey |
Jessica Jobe jjobe@usgs.gov U.S. Geological Survey |
Richard Briggs rbriggs@usgs.gov U.S. Geological Survey |
Joseph Powell jpowell@usgs.gov U.S. Geological Survey |
Mark Shapley shap0029@umn.edu Continental Scientific Drilling Facility |
Bruce Finney brucefinney@isu.edu Idaho State University |
Glenn Thackray glennthackray@isu.edu Idaho State University |
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Characterizing Earthquake-triggered Sedimentation in an Intraplate Setting: Delta Collapse and Turbidite Deposition From the 2020 Mw 6.5 Stanley Earthquake (Idaho, USA)
Category
Subaqueous Evidence for Earthquakes, Coseismic Landslides, Tsunamis and other Cascading Hazards