3-8 Using paleoclimate records to refine age estimates for past earthquakes-- an approach using the sediments of Ozette Lake, Washington

Session: Lakes of the World Through Space and Time: Archives of Climate, Paleoenvironments, Ecosystems, Geohazards, and Economic Resources

Presenting Author:

Authors:

Abstract:

The sediments of Ozette Lake, located on the Olympic Peninsula of western Washington, preserve a record of past Holocene earthquakes along the northern portion of the Cascadia subduction margin. During these events, which occurred at 300- to 500-year intervals, earthquake shaking led to subaqueous slope failures and the formation of turbidites. Sediments deposited in Ozette Lake between earthquakes, moreover, show decadal-scale variations in color, magnetic susceptibility, clay content, organic carbon content, density, and computed tomography (CT) intensity. We applied the dynamic time warping technique to compare CT intensity to historical, instrumental measurements of regional cool-season precipitation and revealed a strong correlation, indicating that the lake sediments preserve a record of decadal-averaged fluvial sediment discharge since 1900 CE. Comparison of CT intensity patterns from older strata preserved deeper in the lake stratigraphy to two independent, regional paleo-precipitation reconstructions similarly suggests that the sediments record variations in hydroclimate over the past 1300 years. By placing earthquake-triggered turbidites in the context of wet and dry periods in these tree-ring and oxygen-isotope based reconstructions, we derive radiocarbon-independent dates for the past four Cascadia megathrust earthquakes that are within the uncertainty of a radiocarbon age-depth model but are more precisely estimated.  More precise dates for event layers in this and other regional lakes provided by paleoclimate data have the potential to help address ongoing questions about past earthquakes in Cascadia and elsewhere..

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7329

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.