Abstract
Abstract. We present an investigation of the disturbance history of an old-growth Douglas-fir (Pseudotsuga menziesii) stand in South Beach, Oregon, for possible growth changes due to tsunami inundation caused by the 1700 CE Cascadia Subduction Zone (CSZ) earthquake. A high-resolution model of the 1700 tsunami run-up heights at South Beach, assuming an “L”-sized earthquake, is also presented to better estimate the inundation levels several kilometers inland at the old-growth site. This tsunami model indicates the South Beach fir stand would have been subjected to local inundation depths from 0 to 10 m. Growth chronologies collected from the Douglas-fir stand shows that trees experienced a significant growth reductions in the year 1700 relative to nearby Douglas-fir stands, consistent with the tsunami inundation estimates. The ±1–3-year timing of the South Beach disturbances are also consistent with disturbances previously observed at a Washington state coastal forest ∼220 km to the north. Moreover, the 1700 South Beach growth reductions were not the largest over the >321-year tree chronology at this location, with other disturbances likely caused by climate drivers (e.g., drought or windstorms). Our study represents a first step in using tree growth history to ground truth tsunami inundation models by providing site-specific physical evidence.
Highlights
Recent studies have demonstrated the utility of using treering growth chronologies for assessment of tsunami and earthquake impacts on coastal environments (Buchwal and Szczucinski, 2015; Kubota et al, 2017; Wang et al, 2019)
We presented a series of tree-ring data from an old-growth Douglas-fir forest in South Beach, Oregon, that show significant growth reduction at the time of the 1700 CE Cascadia Subduction Zone earthquake relative to control sites
Due to significant variation in the South Beach topography, several areas are predicted to experience water levels up to 17 m and a range of inundation depths up to 16 m; the location of the old-growth stand may be subjected to a range of inundation depths from 0 to 10 m
Summary
Recent studies have demonstrated the utility of using treering growth chronologies for assessment of tsunami and earthquake impacts on coastal environments (Buchwal and Szczucinski, 2015; Kubota et al, 2017; Wang et al, 2019). Ground motion caused by the megathrust earthquake can cause significant forest disturbance by toppling trees, damaging root systems, severing limbs and crowns, inducing damaging landslides, or altering the hydrology of a stand, among other potential effects (e.g., Sheppard and Jacoby, 1989). These disturbances appear in the tree-ring record of surviving trees as sudden growth suppression events (when there is damage) or growth increases in the case of reduced competition from adjacent damaged trees
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