There is a subduction zone called the Cascadia that exists for 1,100 kilometers (~680 miles) that runs down the coast of the left side of North America... a huge fault line that runs from northern California up to Vancouver Island in southern British Columbia, Canada.
The Cascadia Subduction Zone wasn't considered one of the major movers and shakers of tectonic plates until fairly recently - 20 years or so, but recent discoveries have shown that the fault produces earthquakes of magnitude 8 or larger at irregular intervals, averaging about 500 years.
According to radiocarbon dating, there was a big one somewhere between 1690 and 1720AD that affected some 900 kilometers (560 miles) of that fault.
But no one knew just how big or bad it was.
Back in 1996, researchers in Japan figured out that a tsunami that smashed into Honshu in 1700 was linked to geologic data from the Cascadia Subduction Zone.
Now, that radiocarbon dating isn't an exact science - what with a 30-year guesstimate, so scientists did some tree ring dating on some old trees and found it likely that there was a seismic event between 1699 and 1700.
More research estimated the epicenter in British Columbia, with firsthand reports suggesting it occurred at around 9PM... according to First Nations witnesses on Vancouver Island, BC, Canada, when the shaking stopped, a tsunami formed and sucked everyone and everything near the coast out into the ocean.
Visual evidence below of the tsunami's affect in Oregon in 1700AD:
|A sand layer from the 1700 Cascadia tsunami covers the remains of a Native American fishing camp exposed in a bank of Oregon's Salmon River.|
"We have collected more evidence, made rigorous interpretation of it, and modeled the earthquake source and tsunami propagation by using the latest techniques," explains Geological Survey of Japan seismologist Satake Kenji (surname first, who was also the lead author of the report. "We confirmed that the 1700 earthquake was magnitude 9."
A 9M earthquake releases as much energy as the U.S. nowadays uses in one month.Okay, perhaps a little less... that earthquake would have to shake at the level for a few minutes... still, you get the idea. It was freaking powerful.
For further reference, the March 11, 2011 Tohoku earthquake that shook the north east corner of Japan and spawned some deadly tsunami that nearly caused multiple nuclear meltdowns in nuclear power generating plants at a facility in Fukushima-ken.
A tsunami occurs when an earthquake causes part of the continental plate underwater to bounce upward, warping the sea floor and then raising the water upwards... forming a wave. That's it basically.
Now lest one think that earthquakes are one-sided and that Japan has been bending over and taking it in the butt with tsunami, sometimes Japanese earthquakes cause tsunami that hit the left coast of North America.
Uh... two earthquakes in Japan back in 1854 caused tsunami to crash into California and Oregon... but those were minuscule 0.3 meter (1-foot) high tsunami.
Japanese scientists believe that the tectonic faults in Japan simply face in a direction that will not cause massive tsunami to hit North America. Or maybe it needs stronger earthquakes in the 9M range.
Want some more sarcastic good news? Geological Survey of Canada seismologist and report co-author Kelin Wang says that with the Cascadia Subduction Zone fault wedged in place thanks to two locked geological plates under the sea floor - it is building up energy, feeling that the chances of another earthquake along the Cascadia fault is coming. "The question is when, and whether the entire length of the subduction zone will rupture like in 1700."
Those two geological plates, though locked in place, are still trying to move towards one another. This causes stress... and one that the Cascadia fault usually releases in about 300 to 500 years (hence me saying 400 years). When it does go - it will be a big earthquake.
Note that the last big one at that fault was 315 years ago... It could be another 200 years, but it could be a lot sooner and western Canada and east Japan will be at severe risk.
This isn't fear-mongering... it's a fact.