In order to understand what the Cowichan and Nuu Chah Nuulth people experienced and described it is necessary to take a look at the Plate Tectonic setting of the the Juan de Fuca region.
The map above shows the plate tectonic setting of the area affected by the 1700 earthquake. The Explorer, Juan de Fuca and Gorda plates are being formed along their respective spreading ridges and they are being pushed ("subducted") underneath the North American Plate along the subduction zone marked in black. The Juan de Fuca Plate is subducting at a rate of around 4.5 cm/year.
Click on the map to see an animated view of the movement of the Juan de Fuca and Pacific plates.