An important factor in estimating a tsunami hazard from a particular source is knowledge of what previous tsunamis from that general region have done. The record of these effects is far from complete for the U.S. West Coast. Given a return rate of 100 to 200 years for many great Pacific earthquakes, and the changes in the population density, coastal development, and coastal area usage since the 19th Century, the hazard from a repeat of these events is significantly increased. Of the 13 tsunamis with amplitudes of 1 meter or more which occurred on the West Coast, only the latest two, 1960 and 1964, caused damage of more than a few thousand dollars. These waves would not have been particularly noteworthy had they occurred in the 19th Century or early 20th Century; reports of their effects would be limited to local sources. Conversely, tsunamis which did occur in the 18th Century without causing significant damage could be destructive if they are repeated in the future. Automatic recording tide gages were installed at San Diego and San Francisco, California, and Astoria, Oregon in 1854, the earliest operated in the Pacific. The publication of newspapers on the West Coast began at a somewhat earlier date. Using contemporary records, extant tide gage records, and a tide prediction computer program, this project will improve the quality of the historical record by adding new descriptive and quantitative data, correcting errors in existing knowledge, and reducing the uncertainty of the source and effects of reports of early tsunamis. Analyses of the resulting improved data base will show the unique features of the hazard. This information is essential to the design of effective tsunami warning systems and other counter measures.
