Paleoseismology

Paleoseismology is usually restricted to geologic regimes that have undergone continuous sediment creation for the last few thousand years, such as swamps, lakes, river beds and shorelines.

It was thought for some time that there was low seismic hazard in the region because relatively few modern earthquakes have been recorded.

All of these comforting notions were shattered by paleoseismology studies showing evidence of extremely large earthquakes (the most recent being in 1700),[2] along with historical tsunami records.

In effect, the subduction zone under British Columbia, Washington, Oregon, and far northern California, is perfectly normal, being extremely hazardous in the long term, with the capability of generating coastal tsunamis of several hundred feet in height at the coast.

Periodically a slip will occur which causes the coastal portion to reduce in elevation and thrust toward the west, leading to tsunamis in the central and eastern north Pacific Ocean (with several hours of warning) and a reflux of water toward the coastal shore, with little time for residents to escape.