Lacustrine paleoseismic investigation in the North Washington Cascade Range

Lacustrine paleoseismic proxies observed within the Northern Cascade Range (WA, USA) may provide insights into the Late Pleistocene through the Holocene earthquake record of the Pacific Northwest. Multibeam bathymetry, sub-bottom CHIRP, and sediment core data recently collected from Lake Chelan comprise an ideal dataset to investigate the spatial and temporal distribution of significant (over MMI V-V1/2) strong ground motion events that have impacted the region. Eighteen percussion-driven gravity cores and 26 mini-piston cores provide ground-truthing to event horizons in the upper ~3.5m of lake sediment. Based on core-to-seismic correlations and deposit geometries, the mapped horizons are associated with sandy turbidite beds, volcanic tephra, fires, floods, and other environmental changes within the watersheds. Our qualitative and quantitative approach relies on the distribution of dated paleoseismic proxies within Lake Chelan to describe historical earthquakes' relative distribution and magnitude. Understanding how large megathrusts and shallower crustal earthquakes are recorded in lacustrine environments is a field of research now coming into sharp focus; the goal of our work is to build on the existing lacustrine paleoseismic observations and techniques as well as to refine the earthquake catalog for the Pacific Northwest.
Boe Derosier, Dr. Daniel Brothers, Peter Dartnell, Drake Singleton
US Geological Survey, Pacific Coastal and Marine Science Center
Dr. Brian Sherrod
US Geological Survey, Earthquake Science Center
Dr. Phil Long
Lake Chelan Research Institute
Presentation given at North Coast & Cascades Science Days, 2024
go.nps.gov/sciencedays
[NOCA]