How Do Large Lakes in the Seattle Area Respond to Different Sources of Seismic Shaking? Revisiting Lake Washington and Lake Sammamish With New High-Resolution Data
Description:
The Puget Sound region is susceptible to a variety of seismic hazards, including intraslab and crustal earthquakes, as well as megathrust earthquakes from the Cascadia Subduction Zone. To better characterize these hazards, the USGS is working on a multiyear project at sites spanning the Olympic Peninsula coast to the eastern Cascades to understand how sources of ground motion from different faults manifest in the lake basins. Here, we present results from two large lakes in the Seattle area: Lake Washington and Lake Sammamish because both lakes are located within a zone projected to experience strong to very strong ground motions during a Cascadia megathrust event. Additionally, these lakes are also surrounded by several crustal faults, and have experienced historical shaking due to deep intraslab earthquakes. The USGS led two multi-week field campaigns in 2021 (Lake Sammamish) and 2024 (Lake Washington) acquiring high-resolution bathymetry data, chirp subbottom profiles, and sediment cores. In both lake basins, bathymetric data reveal multiple slope failures along the flanks, while chirp data uncover details of post-glacial sedimentation patterns, including evidence for older, buried mass transport deposits and deformation associated with the Seattle fault. Mazama ash deposits identified throughout the Lake Sammamish stratigraphy, in cores and subbottom data, provide chronological markers that are used to build preliminary age-depth models. Our preliminary interpretation suggests that most of the larger subaqueous mass transport deposits visible in the bathymetry are pre-Holocene, whereas previous work suggests that large failures observed in Lake Sammamish may be linked to earthquake(s) in the Seattle and Saddle Mountain fault zones in 923-924 CE. The apparent absence of subsequent large-scale slope failures here raises questions about basin’s response to shaking from Seattle fault ruptures. Ongoing work includes detailed stratigraphic mapping, additional age dating of turbidite event deposits, and comparison with a series of lakes across latitudinal and longitudinal gradients in the Pacific Northwest.
Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments [Poster Session]
Type: Poster
Date: 5/1/2024
Presentation Time: 08:00 AM (local time)
Presenting Author: Jared
Student Presenter: No
Invited Presentation:
Authors
Jared Kluesner Presenting Author Corresponding Author jkluesner@usgs.gov U.S. Geological Survey |
Jenna Hill jhill@usgs.gov U.S. Geological Survey |
Daniel Brothers dbrothers@usgs.gov U.S. Geological Survey |
Brian Sherrod bsherrod@usgs.gov U.S. Geological Survey |
Jamie Conrad jconrad@usgs.gov U.S. Geological Survey |
Boe Derosier bderosier@usgs.gov U.S. Geological Survey |
Drake Singleton dsingleton@usgs.gov U.S. Geological Survey |
Peter Dartnell pdartnell@usgs.gov U.S. Geological Survey |
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How Do Large Lakes in the Seattle Area Respond to Different Sources of Seismic Shaking? Revisiting Lake Washington and Lake Sammamish With New High-Resolution Data
Category
From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments