Skip to comments.Slow Seismic Slip Event Underway in Pacific Northwest
Posted on 09/14/2005 3:20:11 PM PDT by Esther Ruth
Slow Seismic Slip Event Underway in Pacific Northwest By Robert Roy Britt LiveScience Managing Editor posted: 13 September 2005 10:03 pm ET
Updated 2:35 p.m. ET Sept. 14
An important seismic event imperceptible to humans has begun in the Pacific Northwest as predicted, according to the government agency Geological Survey of Canada.
The chance of a major earthquake is 30 times higher now for a roughly two-week period, but the odds are still remote, scientists say.
The event is called episodic tremor and slip (ETS). It involves a slow movement of the Juan de Fuca and North America tectonic plates along the Cascadia margin of southern British Columbia. Faults associated with the plates have been the sites of major earthquakes -- akin to the colossal tsumani-causing quake last December in Indonesia -- every 500 years or so, the geologic record shows. The last such temblor in the area struck on Jan. 26 in the year 1700.
The movement is slower than a traditional earthquake but more rapid than the normal creep associated with the fault. It runs in the reverse direction of the normal creep.
(Excerpt) Read more at livescience.com ...
The movement was predicted. Scientists recently learned that these ETS events recur about every 14 months. It has been detected by Global Positioning System instruments.
The event does not mean an earthquake is imminent, but geologists are eager to study it and learn more and they say sooner or later an ETS event is likely to trigger a major quake.
"Compared to the steady year-round stress accumulation, this more rapid stress increase implies that a large subduction earthquake is more likely to happen during the time of an ETS event," the Canadian geologists write.
The slippage and associated minor tremors "are directly related to megathrust (Sumatra-like) earthquake potential," lead geologist John Cassidy and a colleague said in Tuesday's statement. "Neither the tremor nor the slip can be felt."
Odds go up
The slip began Sept. 3 on the Olympic Peninsula of Washington State and has migrated north to the Vancouver Island area, Cassidy wrote. Victoria moved 0.12 inches (3 millimeters) to the West over the course of two days. The events are thought to last six to 15 days.
Cassidy's colleague, Stephane Mazzotti, has done some calculations on the odds of a large temblor.
"The probability of occurrence of a megathrust earthquake is about 30 times higher during this approximately two-week window, than during the rest of the 14.5 month cycle," Cassidy told LiveScience. "Having said that, 30 times a small number is still a small number."
Geologists simply don't know when one of these events will trigger a major quake, Cassidy said.
The immediate importance of the event is that it occurred as predicted and can now be used to improve understanding of the region's seismology.
"By better understanding these events, we will be able to better predict the effects (and perhaps timing) of future magnitude 9 earthquakes along the West Coast," Cassidy and his colleague write.
A separate study recently concluded that a major earthquake along the fault could be overdue, given clusters of the events seen in the geologic record. Because the fault is offshore, scientists say its rupture could create a devastating tsunami
Drudge has this posted on his sight.
If I remember correctly, the estimate of "every 500 years" is invalid. Averaging the estimated periods between the events doesn't mean anything when there is such a huge disparity between the longest known period between events and the shortest.
I haven't watched this for awhile so don't know if the activity by Mt St Helen is up or just same as usual.
The value of 500 years was calculated by a moving temporal average of a poisson distribution written on a slip of paper and pulled out of a hat.
More evidence of global worming...
That sounds ridiculous. How are you going to stop a trillion tons of rock and make it suddenly move backwards?
Oh, that's bad...
I'm not going to tell my wife about this...and if I time it just right, and the the earthquake does occur...[heh,heh]
Another fault of Bush. He didn't sign the Koyote agreement!
Global warmint, Oz-one hole, Katerina, Tsunami, quakes....
More likely a PDOOMA.
Did kinda stink up the place didn't it. LOL
How is that done?
And because they have information that dates only one prior event. That information is based upon core samples of cedar trees that were submerged after the last quake. The link between that and the great tsunami is largely anecdotal (journals of a Japanese emperor at the time that described the tsunami though it could have been caused by another undersea quake around the same time).
Once again, science is shaming itself by trying to establish trends based upon little precedence, as they are doing with global warming.
By the shifting of even greater magma forces that the trillion tons of rock are floating on.
I think this is going to happen and Seattle may well be obliterated. I really doubt anyone knows when it will happen, though.
Well now...glad I am going to Idaho for the weekend just in case Oregon breaks off and falls into the Pacific.
Oh come on, haven't you ever watched the "Tremors" movies on the Sci Fi channel?
Sounds like a dance: "Seismic slip, let your backbone flip" ...
"An important seismic event imperceptible to humans..."
Just keep an eye on your local rodents. When you see rats scrambling for safety, you can be assured something big is coming your way. (And I don't mean Fat Teddy!)
Don't ask me how I know this, as my reasoning skills are imperceptible to other humans. ;)
The fault could move backwards if you think of it as chunks along each side of the fault. There is never a solid piece on either side of a fault line. A fault line is never straight, but is a series of jagged sections, 5 miles long, 100 miles long which do the actual slipping when an earthqauke happens.
One side of the fault (the Pacific plate) is moving North, the other (the North American plale) is more-or-less stationary. The stationary continental side, or more accurately a section of it, can be pushed so far north by being locked up against the Pacific side, that it eventually slips backward, either slowly like in this case, or all at once like in a big earthquake.
The pressure can build so much that if both sides are still locked enough together, both sides of the fault line move backwards.
But to me this means that the pressure is built up so much that a big quake can happen (especially considering the length of the sections moving.)
Obviously Bush's fault.
He should apologize and take responsibility immediately.
Oh Great! I live 30mi East of Seattle, and I saw two rats cross the road today heading NE, I also saw the same thing last week.
I had slow creep once. Went to the pharmacy and bought some meds and now my creep is back to normal speed.
I thought WA was polluted with demoncrats.