First Advisor

Curt D. Peterson

Term of Graduation

Spring 2000

Date of Publication


Document Type


Degree Name

Master of Science (M.S.) in Geology






Stratigraphic geology -- Holocene, Floods -- Oregon, Floods -- Washington (State), Tsunamis -- Oregon, Tsunamis -- Washington (State)



Physical Description

1 online resource (vi, 166 pages)


Mapping and stratigraphic investigations of back barrier, open-coastal plain sites have been used to establish minimum inundation distances and wave heights of tsunami produced by great subduction zone earthquakes in the central Cascadia margin. Cascadia tsunami deposits have been reported for many coseismic subsidence events in bay marsh settings where tidal-channel features focus tsunami energy. Variable magnitude (8.5±0.5 Mw), frequency (500±300 yr recurrence), and rupture geometry produce widely varying computer model outcomes for Cascadia tsunami inundation. The results presented in this thesis provide specific quantitative data regarding tsunami inundation at the open coast.

Anomalous sand sheets that have been characterized consist of well-sorted beach sand that fine up-section. The thickness of the deposits vary from 45 cm to 0.2 cm, and thin in the landward direction. Many of the sand layers include detrital caps. One to three detritus and mud lamina are intra-layered in the deposits. Marine diatoms and bromine, a marine tracer, increase in concentration at each of the sand layers.


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