posted this the other day. For some reason I keep going back to it. Then digging around I found the information posted at end wondering if this is related and maybe headed to such an event? Just putting it out there.
1700 Cascadia earthquake
The 1700 Cascadia earthquake was a magnitude 8.7 to 9.2 megathrust earthquake that occurred in the Cascadia subduction zone on January 26, 1700.
The earthquake involved the Juan de Fuca Plate underlying the Pacific Ocean, from mid-Vancouver Island in British Columbia, Canada, south along the Pacific Northwest coast as far as northern California, USA. The length of the fault rupture was about 1,000 kilometers (620 miles) with an average slip of 20 meters (22 yards).
The earthquake caused a tsunami that struck the coast of Japan, and may also be linked to the Bonneville Slide.
Evidence supporting the occurrence of the 1700 earthquake has been gathered into the 2005 book The Orphan Tsunami of 1700, by geologist Brian Atwater and others.
The evidence suggests that it took place at about 21:00 on January 26, 1700 (NS). Although there were no written records in the region at the time, the earthquake's precise time is nevertheless known from Japanese records of a tsunami that has not been tied to any other Pacific Rim earthquake. The most important clue linking the tsunami in Japan and the earthquake in the Pacific Northwest comes from studies of tree rings (dendrochronology) which show that red cedar trees killed by lowering of coastal forests into the tidal zone by the earthquake have outermost growth rings that formed in 1699, the last growing season before the tsunami. Local Indigenous American oral traditions describing a large quake also exist, although these do not specify the date.
The period for these earthquakes is arround 300-400 years
[link to www.world-earthquakes.com
Based on our existing knowledge of plate tectonics -- where the Earth's crust is broken into many solid "plates" that typically collide and push under (subduct) or scrape by each other to create the largest earthquakes -- there is not a large enough single crustal plate boundary to create a magnitude 10.5 earthquake.
The largest measured earthquake, so far, is the 1960 magnitude 9.5 Chilean earthquake, which occurred along a subduction zone. California's largest earthquake was the 1857 magnitude 7.9 Fort Tejon earthquake. While both of those quakes are very strong in their own rights, they are significantly smaller than a magnitude 10.5 earthquake. A magnitude 10.5 earthquake would release about 32 times more energy than a magnitude 9.5.
There are two types of tectonic plate boundaries along the West Coast of the U.S. and Canada. The San Andreas fault forms a plate boundary where the plates scrape along each other (a transform boundary) from the Imperial Valley in the south to Cape Mendocino in the north. North of Cape Mendocino, the oceanic plate is subducted or pushed under the continental plate along a plate boundary running parallel to and off the Northern California coast all the way to Aleutian Islands of Alaska.
Based on information gathered from the world's largest earthquakes, it would take a rupture 6,000 miles long along a subduction boundary to produce a magnitude 10.5 earthquake. That would be a rupture from the North Pole to the Equator, and that type and size boundary doesn't exist.
[link to www.conservation.ca.gov
Here's a pretty cool website I found he has some graph's about the plates, information other neat stuff
[link to www.backwoodshome.com