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SCI/TECH: Strange Tremors Shake San Andreas Fault

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posted on Dec, 12 2004 @ 04:35 PM
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Seismologists are puzzling over a series of rare tremors never before recorded in the San Andreas Fault - or in a fault of the same type, for that matter. Parkfield, CA didn't feel the shaking deep beneath their feet, but scientists monitoring the area have recorded 110 incidents of "chatter" in the last three years. This chatter occurs well below the average depth of an earthquake - up to 40 miles below the surface - and is usually seen related to magma movement in volcanoes such as Mount St. Helens. Earthquakes normally occur around 10 miles below the Earth's crust. Seisimologists have not determined any magmatic activity related to these tremors, but are hard-pressed to explain exactly what they mean.
 



www.sfgate.com
Seismic researchers are monitoring the strange vibrations closely. But whether the faint underground tremors -- termed "chatter" by some seismologists -- portend an increased likelihood of a major quake in the area is an unsolved puzzle.

Robert Nadeau, a geophysicist at the UC Berkeley Seismological Laboratory, charted more than 110 of the faint vibrations since they were first detected by the lab's High Resolution Seismic Network in Parkfield three years ago. What concerns Nadeau and his colleagues is that the epicenter of the great 1857 Fort Tejon earthquake, whose magnitude has been estimated at 7.8 to 8, was located almost exactly where the deep tremors are now occurring -- beneath the San Luis Obispo County village of Cholame, some 17 miles south of Parkfield.

The episodes of chatter last from four to 20 minutes and are being recorded from as deep as 40 miles beneath the surface -- up to four times the depth of normal earthquakes, which originate in what scientists call the "seismogenic zone." That zone reaches no deeper than 9 or 10 miles below the Earth's surface.

What's most striking is that deep tremors like the Cholame series have never been recorded before on a strike-slip fault such as the San Andreas, Nadeau said.


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The most concerning aspect of these tremors is their location. In 1857, a massive earthquake estimated at a magnitude 8 was centered at the exact area where the current chatter is occurring. That earthquake ruptured the San Andreas for an estimated 225 miles and caused massive ground rolling. Due to it's then sparse population, only two people died and very little damage was reported. While still a relatively rural area, growing communities are well within the "danger zone" if a large quake were to strike. The damage and loss of life could be significant if these tremors are preceding another tremblor like the 1857 Ft. Tejon quake or the similar 1906 San Francisco quake.

A report published on Friday noted that "...future increases in San Andreas Fault tremor activity may signal periods of increased probability for the next large earthquake on the Cholame segment."

Related News Stories:
MSNBC.com


[edit on 12-12-2004 by Banshee]




posted on Dec, 12 2004 @ 04:56 PM
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Wow! Is it a sign or a warning of something big that may be coming? The death and destruction would surely be tragic, but from a science point of view, it sure is cool...
Thankfully I live on the other side of the rockies...



posted on Dec, 12 2004 @ 05:51 PM
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Really, what’s up with the increased seismic and magmatic activity on the West coast this year?



posted on Dec, 12 2004 @ 08:51 PM
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Hmmm. I'm getting a bit concerned. It seems that geographic activity has been on the rise lately. Well let's just hope Yellowstone doesn't blow. Thank goodness I live in Illinios. Then again we just had a noticable earthquake not to long ago, unusual for Illinios.



posted on Dec, 12 2004 @ 08:53 PM
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It may be that todays instruments are now sensitive enough to measure the deeper and more unusual tremors.



posted on Dec, 12 2004 @ 11:40 PM
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I wonder if there is any relation between this and the odd quake swarm that happened in CA back in September. There was a huge swarm more consistant with magma movement that took place in an area without a volcano. I'm still wondering about the possibility of the formation of a new super volcano. This area of the planet has the highest concentration of such systems anywhere in the world.



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