The San Andreas is open to the ocean at both ends. The southern end is open to the Gulf of California while the northern end is open to the Pacific Ocean just north of San Francisco.

Most of the subduction zones are located under the ocean. The one everyone is concerned with now is the Cascadia Subduction Zone. The Cascadia Subduction Zone is a very long sloping fault that stretches from mid-Vancouver Island to Northern California. It separates the Juan de Fuca and North America plates. New ocean floor is being created offshore of Washington and Oregon. The last known great earthquake in the northwest was in January 1700, just over 300 years ago. Geological evidence indicates that great earthquakes may have occurred at least seven times in the last 3,500 years, suggesting a return time of 400 to 600 years. The quake was thought to have been M>9.0+.

Scientific measurements show that the Juan de Fuca plate is moving inland at a rate of about 4mm per year (quite slow for a subduction zone). Over a 500-year period that strain release would account for a 20-meter displacement and over 900 years a 45-meter displacement. This translates to a tremendous amount of locked potential energy that when released can cause a very large quake in the order of magnitude of about 8.5 to 9.5! So with these measurements this evidence implies that indeed the plates are locked and sometime in the near future the plates will give way resulting in a large quake.

“New research indicates that a massive earthquake could occur directly underneath the Oregon Coast Range and the western portion of the Willamette Valley. For nearly 15 years, scientists have warned that a magnitude 8 or 9 earthquake could strike about 30 miles offshore and rock the coast, causing severe shaking and huge tsunamis. However, recent data gathered from satellites by scientists at Oregon State University and three other institutions show that the colossal quake could hit much farther inland and cause more severe damage to a larger area -- including the more populated cities of the Willamette Valley such as Portland, Salem and Eugene.”

“The research team found that the locked portion of the Cascadia Subduction Zone -- where the eastward-moving Juan de Fuca Plate plunges under the western-moving North American Plate -- extends beneath the Coast Range and as far as the western side of the Willamette Valley.”

“The researchers expected to find little movement because of the lack of earthquakes and previous data that showed little uplift in central-western Oregon, something commonly associated with a locked subduction fault. Instead, they found that the ground is moving nearly half an inch a year toward the northeast. The rapid velocity worries earthquake researchers and indicates that the underlying plates are locking up rather than sliding by each other, resulting in incredible strain.”
Marine geologist Hans Nelson (Texas A&M University's College of Geosciences) and paleoseismologist Chris Goldfinger (Oregon State University's College of Oceanic and Atmospheric Sciences) are building on the idea of Canadian scientist John Adams that shaking from Cascadia subduction zone earthquakes should generate sandy density currents. Such turbidity currents flow down deep-sea channels on the continental margin and deposit turbidite sand layers that record paleoseismic events.

"We are now coring into the deep-sea bottom of these channels to collect turbidite layer evidence of past seismic events," Nelson said. "Cascadia is an excellent area to develop this deep-sea paleoseismic record because 7,600 years ago, when Oregon's Mt. Mazama erupted, forming Crater Lake, 100 times more volcanic ash than that of Mt. St. Helens' 1980 eruption was deposited in the Columbia River drainage area."

"We have found that 12 turbidite bed layers occur for 600 km along the Cascadia margin, above the first bed with Mazama ash," Nelson said. "The best explanation is that great earthquakes on the subduction zone have triggered these events about every 600 years since the Mt. Mazama eruption 7600 years ago. Our deep-sea paleoseismic record now has verified the coastal record, extended it reliably back in time for thousands of years more and shown that the Pacific Northwest faces the hazard of future great earthquakes. Take Care…Don in Hollister

http://www.4j.lane.edu/partners/eweb/ttr/quake/risk.html

http://www.scienceblog.com/community/older/2001/D/200114348.html

http://www.oregongeology.com/earthquakes/Coastal/OrGeoEqNTsu.htm

http://www.winfinity.com/cff/Info/tsu-inf-st.html

http://seattlepi.nwsource.com/connelly/joel02.shtml

I always thought that Alaskan's endured a big quake in the 60's?, but I guess it was a quake that was focused offshore and caused a tsunami to wipe out a village there. The damage was quite extensive to the town's roads and buildings and resultant shorline which was submerged after the event.

I've been to S.F. on down to Monterey and Salinas a few times but never experienced any tremors while there. Beautiful scenery though. Quakes were the last thing on my mind. Big Sur and Santa Cruz were absolutely breathtaking for me, a small town'er from N. Ontario.

In Ottawa of all places, Don, I was in bed about eight o'clock in the am last year. Laying in a water bed on the cement slab basement floor and still hypnogogic, I felt vibrations from what I thought was a cement truck or perhaps a dump truck ...or two. It was a tremor!. I remembered the shaking half an hour later only because someone mentioned it was a quake and realized that there were no heavy trucks that morning, nor was there any reason for them to be anywhere close to the house.

I think we're situated on a very ancient fault line that extends from the east end of Lake Superior south-east toward Oka, P.Q., one of the world's most abundant rare earth mineral deposits.
AS far as I know, this is a stable granitic plate we're on here. A geologist once told me that the soil around Ottawa and surrounding area is somewhere in between a soil and a rock because it has a crystaline structure to it. Apparently, it's not stable, and a real quake would likely cause a lot of damage to certain areas here. Yikes!. But I doubt we're in any real danger.

Like my grandmother used to say, don't worry lad, t'might never 'appen.

[ 03 December 2004: Message edited by: Fidel ]

The Charlevoix Seismic Zone (CSZ) of Quebec is one of the most seismically active regions of Canada. It isn’t as active as the West Coast, but it does have a fair share of them. There are more than 200 micro-earthquakes recorded there every year and five damaging earthquakes in the magnitude (M) 6 range have occurred there (in 1663, 1791, 1860, 1870 and 1925). Take Care…Don in Hollister

Charlevoix-Kamouraska Region-1663
Charlevoix-Kamouraska region, Quebec; Widely felt. Reports of vast landslides in the St. Lawrence, Batiscan and Saint-Maurice valleys. Magnitude: 7.0
Source: Geological Survey of Canada, Natural Resources Canada. Canadian Geophysical Atlas

Near Montréal-1732
Near Montréal, Quebec. Widely felt. About 300 houses damaged in the city of Montréal. No injuries. Magnitude 5.8
Source: Geological Survey of Canada, Natural Resources Canada. Canadian Geophysical Atlas

Charlevoix-Kamouraska Region-1791
Charlevoix-Kamouraska region, Quebec. Widely felt. Some damage at Baie-Saint-Paul and Les Éboulements. Magnitude 6.0
Source: Geological Survey of Canada, Natural Resources Canada. Canadian Geophysical Atlas

Charlevoix-Kamouraska Region-1860
Charlevoix-Kamouraska region, Quebec. Widely felt minor damage at Baie-Saint-Paul. Magnitude 6.0
Source: Geological Survey of Canada, Natural Resources Canada. Canadian Geophysical Atlas

Charlevoix-Kamouraska Region-1870
Charlevoix-Kamouraska region, Quebec. Widely felt minor damage at Baie-Saint-Paul. Magnitude 6.5
Source: Geological Survey of Canada, Natural Resources Canada. Canadian Geophysical Atlas

Charlevoix-Kamouraska Region-1925
Charlevoix-Kamouraska region, Quebec; the earthquake was widely felt and caused damage along the St. Lawrence River, near the epicentre, and at Quebec City, Trois-Rivières and Shawinigan. Magnitude: 6.7
Source: Geological Survey of Canada, Natural Resources Canada. The National Atlas of Canada, 5th edition.

Temiscaming Region-1935
Temiscaming region, Quebec-Ontario border; widely felt; there was minor damage at Temiscaming, Quebec, and North Bay and Mattawa, Ontario. Magnitude: 6.2
Source: Geological Survey of Canada, Natural Resources Canada. The National Atlas of Canada, 5th edition.

Saguenay Region-1988
Saguenay region, Quebec; some minor damage was caused at Jonquière, Chicoutimi, La Baie and Quebec City. Magnitude: 6.0
Source: Geological Survey of Canada, Natural Resources Canada. The National Atlas of Canada, 5th edition.

Ungava Peninsula-1989
Ungava Peninsula, Quebec; the first earthquake in eastern North America to have produced surface faulting. Magnitude: 6.3
Source: Geological Survey of Canada, Natural Resources Canada. The National Atlas of Canada, 5th edition.

Mont-Laurier-1990
Mont-Laurier, Quebec; one of the largest earthquakes to have occurred in eastern North America during the past decade. Magnitude: 5.0
Source: John Adams, Geological Survey of Canada. Poster - The Mont-Laurier Earthquake of October 1990

http://www.cseg.ca/recorder/pdf/2004/10oct/10oct_08.pdf

Wondering, on a purely personal note ... I have a net.friend, Sue Hough, a seismologist with a bent for popular science who's written a recent book called "Earthshaking Science: What We Know (and Don't Know) about Earthquakes." (Shameless plug, I know, but I have no problem recommending her book, it's great!)

Sue is presiding over a lecture about “Dynamic Stress Change, Triggered Earthquakes and Aftershocks” at the Fall AGU meeting being held in San Francisco this month. It’s a five-day event, which I will be attending.

Triggered earthquakes and aftershocks are my prime interests. The aftershocks aren’t the ones that occur in the area of the main event. They are those that are triggered thousand of miles away. The term used is Far Field Aftershocks (FFAs) and these are quakes that occur after an M>7.0 quake and larger.

The recent M>4.3 quake in Northern California in the area of Eureka may have been triggered by FFAs from the 102-106° rings from the Indonesia and the Hokkaido quakes. The quake was in the middle of both rings, but what makes this series of rings unique is that they passed through the area going in the opposite directions. The Hokkaido ring came into the area from the east and the Indonesia ring came into the area from the west. The rings generated by a large quake will last for about 10 days.

I have a program that allows me to see where the rings will occur. When a M>7.0 quake or large occurs it generates 10 rings. I put the epicenter of the main event in the program and will generate the rings on a map. This allows me to see where they will occur.

0-5 degrees
9-10 degrees
17-19 degrees
34-36 degrees
43-45 degrees
59-61 degrees
71-73 degrees
102-106 degrees
142-146 degrees
176-180 degrees

The strongest triggering is always expected to be along the shadow zone boundary between 102-106 degrees from the epicenter and at 142-146 degrees.

The problem with the FFA map is that you never know where the quake will be triggered. The quake that is triggered would most likely have occurred a couple of days later were it not for the FFAs. Many more years of research is going to be required for it to be of any use. Then again it may never be of any use simply because you can’t get the exact location of the next triggered quake. In order for it to be of any use you have to get the location, date and magnitude. Currently that can’t be done.

story

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Originally posted by Rufus Polson:
You know, this thread title is gruesome. I keep picturing Fidel being gradually sucked under a fault line and crushed; terrible thing to happen to a comrade!

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