Methods Coastal wetlands of Seaside, Oregon, consist of the Necanicum River, Neawanna Creek, Neacoxie Creek, and Stanley Lake. These low lying areas represent protected environments with high potential to preserve evidence of coseismic subsidence and tsunami inundation. All cores were logged at one centimeter intervals for sediment lithology, special characteristics such as grading and laminations, and contact relationships. Sand layers are of significant interest, and when found are examined for sorting, grading, and abruptness of contacts above and below. Examination of contact relationships distinguishes between changes in depositional environment caused by coseismic subsidence, uplift, or gradual submergence.
Intruded contacts show irregular lithologic interfaces, for example between sand and mud or peat.
These contacts produced by sand fluidization and injection can result from coseismic liquefaction. Table 1 . Aerial photos, topographic maps, and orthophoto maps were used to identify additional wetland sites for examination by coring, trenching, and cutbank examination. Radiocarbon samples were collected from trenches or pound cores, allowing for an undisturbed stratigraphic section. Ideal samples for radiocarbon dating included small sticks and spruce or pine cones in contact with the target tsunami sand layers.