TREE-RING EVIDENCE FOR AN AD 1700 CASCADIA EARTHQUAKE IN WASHINGTON AND NORTHERN OREGON

Geologic evidence and radiocarbon dating indicate that a subduction ea rthquake, or series of earthquakes, occurred about 300 yr ago along th e Pacific Northwest coast of the United States. Some radiocarbon dates come from remnants of the myriad trees drowned by coincident subsiden ce. At several coastal lowland locations in Washington and northern Or egon, we located two or more trees that survived partial submergence a nd lived to the 1990s. Many of them were damaged by shaking and/or inu ndation. Some survivors recorded the event(s) by anomalous changes in ring width or anatomy of their annual rings, The disturbance initiatin g 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 dat ed evidence of disturbance extends along about 100 km of coastal Washi ngton and northern Oregon, These results support the inference that a great (M-W similar to 8) earthquake or larger at the Cascadia subducti on zone generated the historical tsunami that struck Japan in January 1700.