What are the Cascadia greatest earthquake?

Geological evidence indicates that 13 great earthquakes have occurred in the last 6000 years. In the interval between great earthquakes, the tectonic plates become stuck together, yet continue to move towards each other. This causes tremendous strain and deformation of the Earth's crust in the coastal region and causes ongoing earthquake activity.

At 1700 01 26 UTC, along the west coast of North America, one of the world's largest earthquakes occurred. In this great earthquake a 1000 km length rupture is formed by the undersea Cascadia thrust fault from mid Vancouver Island to northern California in a great earthquake. Quake generated tremendous shaking results a huge tsunami that swept across the Pacific. The Cascadia fault is the boundary between two of the Earth's tectonic plates: the smaller offshore Juan de Fuca plate that is sliding under the much larger North American plate. 

 
The Cascadia fault is the boundary between two of the Earth's tectonic plates: the smaller offshore Juan de Fuca plate that is sliding under the much larger North American plate.

The earthquake left unmistakeable signatures in the geological record as the outer coastal regions subsided and drowned coastal marshlands and forests that were subsequently covered with younger sediments.
 

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