Tree-ring evidence for an A.D. 1700 Cascadia earthquake in Washington and northern Oregon

Abstract

Geologic evidence and radiocarbon dating indicate that a subduction earthquake, or series of earthquakes, occurred about 300 yr ago along the Pacific Northwest coast of the United States. Some radiocarbon dates come from remnants of the myriad trees drowned by coincident subsidence. At several coastal lowland locations in Washington and northern Oregon, we located two or more trees that survived partial submergence and lived to the 1990s. Many of them were damaged by shaking and/or inundation. Some survivors recorded the event(s) by anomalous changes in ring width or anatomy of their annual rings. The disturbance initiating the changes can be dated to between the growing seasons of A.D. 1699 and 1700. One killed tree has a last ring of A.D. 1699. Tree-ring dated evidence of disturbance extends along about 100 km of coastal Washington and northern Oregon. These results support the inference that a great (M w~8) earthquake or larger at the Cascadia subduction zone generated the historical tsunami that struck Japan in January 1700.