New research from University of Washington geophysicist Heidi Houston has found that the Cascadia Fault, off the coast of the Pacific Northwest, experiences nearly undetectable tremors every 12 to 14 months. These tremors, reports The Seattle Times, can sometimes release as much energy as a magnitude 6.8 earthquake. They are part of what's called a slow slip, basically an earthquake that releases energy over an extended period of time rather than all at once.
The issue with these slow slips is that, while they themselves may not be dangerous, they slowly put pressure on the fault. At some point that pressure will release in the form of a magnitude 9 earthquake.
An earthquake of that magnitude would be devastating. The recent earthquake in Nepal for instance has claimed at least 4,800 lives so far and measured magnitude 7.8. A magnitude 9 earthquake and resulting tsunami in Tohoku, Japan in 2011 claimed nearly 16,000 lives.
Judging from records of a tsunami in Japan in 1700, the last major Cascadia quake caused a tsunami — and almost certainly would again.
But don't go panicking quite yet (even though, as Crosscut's Knute Berger writes, today is the 50th anniversary of a major quake in Seattle). These mega-earthquakes happen once every 200 to 800 years. Since it's been 315 years ago since the last one, this would put us in the right time frame for one — but the fault could also go another 500 years without incident. There's simply no way to be sure. But this does of course raise a very important question: How prepared are Seattle and the Northwest for an earthquake of this magnitude?
