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The Pacific Northwest is situated on the seismically active Pacific Ocean margin. Seismic activity in the Pacific Northwest is due to the convergence (or moving towards one another) of two tectonic plates, the North American Plate and the Juan de Fuca Plate. Extending from northern California to British Columbia, the Juan de Fuca Plate is being pushed underneath, or subducted by, the North American Plate at a rate of 40 to 50 millimeters per year (mm/yr). Additional seismic activity exists further offshore originating from the Pacific Plate and the Juan de Fuca Plate spreading apart from each other.
Hydrothermal vents on mid-ocean ridges of the northeast Pacific Ocean are known to respond to seismic disturbances, with observed changes in vent temperature1, 2, 3, 4. But these disturbances resulted from submarine volcanic activity; until now, there have been no observations of the response of a vent system to non-magmatic, tectonic events. Here we report measurements of hydrothermal vent temperature from several vents on the Juan de Fuca ridge in June 1999, before, during and after an earthquake swarm of apparent tectonic origin. Vent fluid temperatures began to rise 4–11 days after the first earthquake. Following this initial increase, the vent temperatures oscillated for about a month before settling down to higher values. We also observed a tenfold increase in fluid output from the hydrothermal system over a period of at least 80 days, extending along the entire ridge segment. Such a large, segment-wide thermal response to relatively modest tectonic activity is surprising, and raises questions about the sources of excess heat and fluid, and the possible effect on vent biological communities.
Since Sunday morning 27 February at 0031Z, there has been an ongoing, intense earthquake swarm on the Endeavour segment of the northern Juan de Fuca Ridge. SOSUS has detected 3,742 earthquakes over a 5.5 day period. Event counts were as high as 50-70 per hour which is very similar in scale to past seafloor spreading events at Middle Valley in 2001 and Endeavour in 1999.
ScienceDaily (Apr. 8, 2008) — Seismic activity on the southern Cascadia Subduction fault may have triggered major earthquakes along the northern San Andreas Fault, according to new research published by the Bulletin of Seismological Society of America (BSSA). The research refines the recurrence rate for the southern portion of the Cascadia fault to approximately every 220 years for the last 3000 years.
According to the article, the theory is that “around 2,000 years ago a massive, cataclysmic earthquake abruptly dropped this forest possibly more than 25 feet. Then, somehow, they [tree stumps] were preserved by sand and mud, rather then being destroyed and scattered, as natural erosion might've done… Either a tsunami brought the sand in or the earthquake rattled up so much soil and sand it covered the forest.”
Clue One: Ghost forests
Ghost forests—long-dead trees—stand stark along the coasts of Washington and Oregon. Atwater knew that similar stands of trees in Alaska had been killed after the Prince William Sound earthquake of 1964. He realized that the Alaskan quake had caused parts of the forest to drop below sea level. Tidewater had rushed in, drowning the trees. Over time, tidal mud accumulated and the area became a salt marsh and then a coastal meadow. But the dead trees still stood.
Larger earthquakes only typically happen along or very close to major fault lines (dont think oregon is on one) but dozens of (perhaps not hundreds like this situation) small earthquakes do not indicate that a large earthquake is going to occur soon as kinetic energy is frequently being released.
Originally posted by Telafree
Id say its almost a necessity to learn about earthquakes and volcanos when you live in portland, or any part of the Pacific northwest which is close to lots of volcanos. One of which is still active (mt st helens) and the others, like Mt Rainier and Mt Hood are in active as of this time. Both are expected to blow at some point or another. Ive lived here for almost 11 years and have 11 years of studying geography and vulcanology(sp?) and evertything in between. For example, if you have ash falling, dont let it build up must more then a few inches or it'll collapse your roof. Afterall, it is pulverised rock! Needless to say, the swarm of quakes remind me so much of what Mt St Helens did before she started erupting again that in my opinion, I wouldn't be surprised if that boat comes back with gas and other measurements showing the movement of lava into a new volcano. I just hope that all of us here in Oregon are safe, and to remember, 3 days worth of food and survival tools is what they suggest for an earthquake or volcano, so all you peeps in the area, time to go shopping!
Im fascinated with volcanos and earthquakes, weird, I know, so this is a treat for me to see this in ATS!
Richard A. Lovett
for National Geographic News
April 16, 2008
This weekend scientists will take to the water to try to puzzle out the cause of a "swarm" of mysterious earthquakes that has shaken the seafloor near Oregon in recent weeks.
About 600 earthquakes have been recorded in a small region about 190 nautical miles (350 kilometers) offshore from Yachats, said Robert Dziak, a geophysicist with Oregon State University and the National Oceanic and Atmospheric Administration (NOAA) in Newport, Oregon.
Colored dots show the earthquake "swarm" that struck waters off the shore of Oregon beginning in March 2008.
Scientists are now planning a marine expedition (black line) to help unravel what is causing the mysterious temblors, which were detected by a Cold-War-era system of underwater microphones originally designed to track Russian submarines.
The three-day research cruise, scheduled to begin on Friday, may solve some of these puzzles.
The scientists say they may find lava oozing out onto the seafloor or hot water percolating up from magma-heated undersea hot springs. They could also come across colder water squeezed out of the underlying crust by tectonic forces.
A response cruise aboard the R/V Wecoma is scheduled to depart Newport, Oregon on Friday, April 18. Ship will be conducting CTD operations.
Originally posted by verylowfrequency
reply to post by DearWife
Thanks again, DearWife. I'll look forward to the results of the 3 hour (day) tour. The weather started getting rough, the tiny ship was tossed....
Pretty cool that they have the resources to go out an do that so quickly.
Interesting sea floor picture as well.
[edit on 17-4-2008 by verylowfrequency]
Figure 1: Map showing the earthquakes and planned response cruise track line. R/V Wecoma is scheduled to depart Newport, Oregon on April 20, 2008
The Bryant Park Project, April 16, 2008 · Earthquakes began rumbling under the ocean off the Oregon coast two weeks ago. More than 600 have been recorded so far. Quakes do come in swarms, says marine geologist Bob Dziak, but not usually like this.
On the hydrophones, the quakes sound like low thunder and are unlike anything scientists have heard in 17 years of listening, Dziak said.
CTD casts conducted at East Blanco Depression, Cascadia Depression (CD)and half-way between swarm center and CD. Although the realtime sensors on the CTD do not show any evidence of hydrothermal emissions from the seafloor, only shore-based measurements will provide definitive analyses of the water samples. Ship ahead of schedule allowing further CTD operations. Hydrophone will not be recovered on this expedition.
Hydrophone deployed. At-sea analysis of CTD samples from the swarm site show do not show evidence of a hydrothermal plume. Conducting further CTDs at other nearby quake sites. View logbook from Bill Hanshumaker, educator at sea.
Animation of earthquakes through time: (Quicktime *.mov).
Courtesy of Del Bohnenstiehl, North Carolina State University.