A Late Holocene sedimentary record of earthquakes and hydroclimate from Ozette Lake, Washington, USA

Abstract Ozette Lake, located on the Olympic Peninsula of western Washington, is ideally situated to provide a sedimentary record of past earthquakes along the northern portion of the Cascadia subduction zone. The lake stratigraphy is punctuated by turbidites, with characteristics typical of those triggered by earthquake shaking as seen in other lakes worldwide. Sediments deposited in Ozette Lake over the past 1300 years between earthquake events show decadal-scale variations in color, magnetic susceptibility, clay content, organic carbon content, density, and computed tomography (CT) intensity. Applying the dynamic time warping technique reveals a strong correlation of CT intensity to historical, instrumental measurements of regional cool-season precipitation, indicating that sediments in the lake preserve a high-fidelity record of decadally averaged fluvial sediment discharge and climate. Correlation 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 decadal variations in hydroclimate. We provide radiocarbon-independent dates for the past four northern Cascadia subduction earthquakes that are within the uncertainty of a radiocarbon age-depth model but are more precisely estimated by placing earthquake-triggered turbidites in the context of wet and dry periods in these tree-ring- and oxygen-isotope-based reconstructions. Paleoclimate-based constraints on the age of event layers in this and other regional lakes have the potential to help address ongoing questions about past ruptures on the Cascadia subduction margin.