Unlike most subduction zones worldwide , no oceanic trench is present along the continental margin in Cascadia . Instead , terranes and the accretionary wedge have been lifted up to form a series of coast ranges and exotic mountains . A high rate of sedimentation from the outflow of the three major rivers ( Fraser River , Columbia River , and Klamath River ) which cross the Cascade Range contributes to further obscuring the presence of a trench . However , in common with most other subduction zones , the outer margin is slowly being compressed , similar to a giant spring . When the stored energy is suddenly released by slippage across the fault at irregular intervals , the Cascadia subduction zone can create very large earthquakes such as the magnitude-9 Cascadia earthquake of 1700 . Geological evidence indicates that great earthquakes may have occurred at least seven times in the last 3,500 years , suggesting a return time of 400 to 600 years . Also , evidence of accompanying tsunamis with every earthquake is seen , as the prime reason these earthquakes are known is through " scars " the tsunami left on the coast , and through Japanese records ( tsunami waves can travel across the Pacific )
Cascadia earthquake of 1700
1700 Cascadia earthquake
Ring of Fire