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Magnitude 3.5 - CHANNEL ISLANDS REGION, CALIFORNIA
2008 December 07 15:39:01 UTC
* Scientific & Technical
* Additional Info
Where can I find...?
* Sunday, December 07, 2008 at 15:39:01 UTC
* Sunday, December 07, 2008 at 07:39:01 AM at epicenter
Location 33.881°N, 119.380°W
Depth 0.1 km (~0.1 mile) (poorly constrained)
Region CHANNEL ISLANDS REGION, CALIFORNIA
* 34 km (21 miles) SSW (205°) from Channel Islands Beach, CA
* 35 km (22 miles) SSW (209°) from Port Hueneme, CA
* 39 km (24 miles) SSW (208°) from Oxnard, CA
* 106 km (66 miles) W (260°) from Los Angeles Civic Center, CA
Location Uncertainty horizontal +/- 1.1 km (0.7 miles); depth +/- 2.8 km (1.7 miles)
Parameters Nph=045, Dmin=27 km, Rmss=0.62 sec, Gp=155°,
M-type=local magnitude (ML), Version=2
* California Integrated Seismic Net:
* USGS Caltech CGS UCB UCSD UNR
Event ID ci14408728
There are only two places in the United States where colliding tectonic plates could cause a major tsunami.... (the other is Alaska.)
The Cascadia subduction zone, is a 680-mile fault that runs 50 miles off the coast of the Pacific Northwest -- from Cape Mendocino in California to Vancouver Island in southern British Columbia.
Scientists say a rupture along the Cascadia fault would cause the sea floor to bounce 20 feet or more, setting off powerful ocean waves relatively close to shore. The first waves could hit coastal communities in 30 minutes or less....
"In the case of the Cascadia Subduction Zone, you could have an area of ocean floor that's 50 miles wide and 500 to 600 miles long suddenly snap back, causing a huge tsunami," Goldfinger said. "At the same time, we could expect some parts of the upper, or North American, plate to sink one to two meters. These are massive tectonic events. Subduction zones produce the most powerful earthquakes and tsunamis in the world."
The Cascadia subduction zone produces great earthquakes, the most recent of which occurred in 1700 and was of moment magnitude (Mw) 9.
Great Cascadia earthquakes generate tsunamis, the most recent of which was probably at least 10 m high on the Pacific coast of Washington, Oregon, and northern California, and up to 5 m high in Japan. These tsunamis threaten coastal communities all around the Pacific Ocean but would have their greatest impact on the U.S. and Canadian west coasts, which would be struck 15–40 minutes after the earthquake.
Strong ground shaking from a Mw 9 plate-boundary earthquake will last three minutes or more and will be dominated by long-period ground motions. Damaging ground shaking will probably occur as far inland as Vancouver, Portland, and Seattle.
The research team, led by Jeffrey McGuire of the Woods Hole Oceanographic Institution, studied past earthquakes along two so-called transform faults on the East Pacific Rise, where tectonic plates are spreading apart.
Next year (2006) an oceanographic expedition led by McGuire will drop sensors along the East Pacific Rise to begin testing the researchers’ hypothesis. The possibility that slow slip transients may herald earthquakes has wider significance, researchers said. Slow slip transients have been detected in subduction zones, where one tectonic plate scrapes under another. The most powerful and dangerous earthquakes occur in subduction zones.
"The possibility that aseismic slip triggers large earthquakes on subduction megathrusts is especially intriguing given the observation that a slow slip transient occurred 15 minutes before the great 1960 Chilean megathrust earthquake," the authors wrote in Nature. "Notably, subduction zones are observed to have higher foreshock rates than continental regions."
Repeated slow slip events observed on the deeper interface of the northern Cascadia subduction zone, at first thought to be silent, have now been found to have unique, non-earthquake, seismic signatures. Tremor-like seismic signals have been found to correlate temporally and spatially with slip events identified from crustal motion data spanning the past six years. During the period between slips, tremor activity is minor or nonexistent. We call this associated tremor and slip phenomenon Episodic Tremor and Slip (ETS) and propose that ETS activity can be used as a real-time indicator of stress loading of the Cascadia megathrust earthquake zone.
If the one-to-one correlation between transient slip and seismic signatures proves to be robust, then the tremor-like seismic signals can provide a real-time indicator of the occurrence of slip. Because slip events on the deep slab interface increase the stress across the locked plate interface located up-dip, it is conceivable that a slip event could trigger a large subduction thrust earthquake (10, 11). Consequently, the onset of ETS activity could lead to recognized times of higher probability for the occurrence of megathrust earthquakes in the Cascadia subduction zone.
June 12, 2008 - This is the wrap-up of this ETS since nothing new has been seen since the tremor on Vancouver Island seems to have died out on June 2. This may have been one of the longer lasting ETSes recorded based on the tremor record. While there were short bursts of tremor in April the more continuous record didn't start until May 4 and was located under the southeast corner of the Olympics (just north of the southern end of Hood Canal. After slowly moving north northwest for about a week it was under the Straights of Juan de Fuca about May 11-12. On May 15 it clearly divided into a patch just moving onto southern Vancouver Island and a second patch in souther Puget Sound (near Olympia). This southern patch only lasted for three days while the northern patch seemed to stick around souther Vancouver Island before moving on northward around May 18-20. While the GPS signals from this ETS were reported to be weaker than some previous ones they can be clearly seen on some stations in northwest Washington as well as southern Vancouver Island (in particular P418 & P436 starting in early to mid May, SC02 & ALBH in mid May, BAMF & CLRS in late May).
Unlike seismic earthquakes, which release sudden shock waves, silent temblors are too slow to cause ground shaking and thus are not considered hazardous. However, some researchers have speculated that silent quakes may be precursors of M8 and M9 mega-temblors that regularly occur in subduction zones--seismically active regions where one tectonic plate is constantly diving ("subducting") beneath another.
These swarms of micro-earthquakes are a clear sign that the silent temblor is adding stress to the fault zone, say the authors, and some day might provide an early warning that a harmless silent event is likely to trigger a destructive mega-earthquake of M8 or larger.
Originally posted by kattraxx
Is it just me, or does it strike anyone else as odd that there are all these small/micro EQ's in the subduction zone along the western U.S.?
[edit on 12/8/08 by kattraxx]