Megaquakes are extremely rare but something may have altered that pattern. In the relatively short time since 2004 there have been megaquakes in Sumatra, Chile and most recently Japan. If you live anywhere in the Pacific Northwest the Geologic forces that can shatter the whole region are building up beneath us right now.
Since I live in a Tsunami zone in the Pacific Northwest, a megaquake is my worst fear. A new article in Outside magazine looks at what's in store for the region when the inevitable megaquake hits. It is coming sooner or later.
Totally Psyched for the Full-Rip Nine
Monster earthquakes are going off all around the Pacific Ocean’s Ring of Fire. Is the West Coast of North America next?
By: Bruce Barcott
Patrick Corcoran is geographer with the who job is to speak to Oregon residents and warn them of the geologic cataclysm that is in store for the region.
He’s a coastal natural-hazards specialist with Oregon Sea Grant, a marine version of an agricultural extension service affiliated with Oregon State University. Corcoran prophesies earthquakes and tsunamis five days a week.
Corcoran discribes a megaquake calling it "A full-rip nine".
By “full-rip nine” Corcoran means a magnitude-9.0 earthquake, the kind of massive offshore temblor that triggered the tsunami that killed 28,050 people in Japan on March 11, 2011. Geologists call them megaquakes. Geologists also call the Northwest coast of North America—from Vancouver Island down to Northern California—one of the likeliest next victims.
The last megaquake to strike this region occurred in 1700.
“The new evidence meant that the Juan de Fuca plate wasn’t sliding easily under the North American plate,” says Yeats. “It meant that the two plates were completely locked.” Pressure has been building and building, for 311 years. If you are a geologist, at this point what runs through your mind is, Holy shit.
HOLY SHIT! That's my reaction too after reading this.
Barcott then walks his readers through what would be likely to happen during a megaquake in vivid detail.
There are more than 900 modern high-rise buildings in Vancouver, Seattle, and Portland. More than half were constructed before 1997, when most urban design codes were updated to reflect the possibility of a CSZ megaquake.
Meanwhile, 50 miles offshore, the movement of the North American plate displaces a massive volume of seawater. A standing wave just a few feet tall appears at the surface, then splits in two. One half heads west toward Japan at a speed approaching 450 miles an hour. It will reach Honshu, the main island, in ten hours. The other half heads east. It will hit the coasts of Oregon, Washington, and Vancouver Island in 20 minutes.
Following a megaquake there is even the possibility of a mini Tsunami in Puget Sound called a Seiche
Barcott's well researched article also says that the quake in store for the Pacific Northwest has the potential to rank as the 3rd largest quake ever recorded. That's why megaquake is my worst fear.
If you live in the Pacific Northwest you need to read this article.
UPDATE: A comment pointed out the possibility of an earthquake triggering a volcanic eruption.
and then I cam across this item from yesterday's news.
Hidden earthquake faults revealed at Mount Hood, Oregon
By Joe Rojas-Burke, The Oregonian
On the northern flank of Mount Hood, a scar in the earth's crust stretches for several miles beneath the fir trees that hide it from airborne observers.
It is the mark of a previously undetected seismic fault that appears to be active -- and dangerous. The last time the fault ruptured, opposing sections of the earth's crust jolted 6 feet apart vertically, leaving a miles-long raised edge, or scarp.
"It was probably a magnitude 6 or 7 earthquake,"
Lidar imaging revealed another fault near Mount Hood that runs to within a mile or two of the Columbia River Gorge, which raises questions about the earthquake resistance of hydropower dams.
"None of the dams were designed with this kind of fault in the analysis," Madin says. "If we find evidence that these faults produce large earthquakes, it might be worth re-examining dam safety." He points out that dam operators have repeatedly adjusted to evolving knowledge about earthquake risks.
While I'm not suggesting that this shallow fault could lead to an eruption of Mount Hood I thought it was interesting enough to share.