Skepticism for claims of earthquake predictability
David Perlman, San Francisco Chronicle Science Editor
San Francisco Chronicle June 16, 2011 04:00 AM Copyright San Francisco Chronicle. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Thursday, June 16, 2011
Earthquakes often seem to send out mysterious electromagnetic signals before the ground ruptures, but what they might mean has sparked controversy for centuries.
Now researchers seeking ways to predict quakes say they have detected those signals in an experiment ripping apart a huge granite boulder near Yosemite.
They liken the signals to the "magnetic pulsations" they say they detected weeks before a 5.6-magnitude quake that struck beneath San Jose's Alum Rock Park on the Calaveras Fault four years ago.
And they believe those pulsations will lead to quake predictions that could save millions of lives.
But the rock-splitting experiment and earlier work by the same research team has drawn a highly skeptical put-down by a leading geophysicist at the U.S. Geological Survey in Menlo Park and most others who have studied so-called seismic-electric signals for decades.
The hopeful researchers are headed by aerospace engineer Tom Bleier, co-founder of a Palo Alto company called QuakeFinder that has been seeking to develop a quake-forecasting technique for more than 10 years.
Bleier and geochemist Friedemann T. Freund of the NASA Ames Research Center in Mountain View tested their "precursor" ideas in an experiment with an 8-ton boulder at Bass Lake in the Sierra, 14 miles from Yosemite's south entrance.
The team drilled four holes deep into the rock, filled them with Bustar, a demolition concrete that expands as it hardens, and watched for signals from sensors sheathing the rock.
Two hours later, "the boulder started to become electrically active" when all the instruments displayed "active signals," they reported.
"What we saw in our artificial experiment was very similar to what we see in nature," Bleier said.
"When you squeeze rocks, they scream," as one of his colleagues put it.
In the scientific journal "Natural Hazards and Earth System Sciences," the team claims the signals they found foretold the mini-earthquake they simulated in the boulder.
In the same journal, Bleier's group said that similar "ultra low-frequency electromagnetic pulses" had registered for up to two weeks before the 2007 Alum Rock quake.
Freund had already measured such signals in laboratory experiments by applying immense pressure to rock slabs, and has developed several physics theories to account for what he calls "pre-earthquake signals."
QuakeFinder has now created a network of instruments at 60 quake-prone sites on all the faults in the Bay Area. He hopes to expand the network to 200 sites from Eureka, Humboldt County, to the Mexican border.
"Being at the right place at the right time with the right instruments, and we're confident that there are a series of distinct electromagnetic signals that exist in the weeks to days before large earthquakes," Bleier said.
At the U.S. Geological Survey in Menlo Park, research geophysicist Malcolm J. S. Johnston has been studying the so-called "precursor signals" that seem to come from some earthquakes. He is convinced they are either unrelated to impending quakes or don't exist.
"The freeways around the Alum Rock quake area are carrying cars, trucks and buses all day and all night, and BART trains are close by. All of them (are) emitting electromagnetic signals all the time. It's called cultural noise, and it's widespread everywhere in California," Johnston said.
He noted the granite rock the researchers split is loaded with quartz, a mineral known for generating electric currents when it's fractured.
"You can prove it yourself by banging two chunks of quartz together and watching the sparks fly," Johnston said. "That's an electromagnetic signal."
When a magnitude-6.0 quake struck on the San Andreas Fault at quake-prone Parkfield in Monterey County in 2004, Johnston and his colleagues had placed a large array of the most sophisticated instruments ever gathered to hunt for electrical and magnetic "precursors" to the Parkfield quake.
They could not detect a single signal. In the Bulletin of the Seismological Society of America, Johnston and his colleagues concluded that the chances of developing an earthquake prediction system based on electric and magnetic signals "seems unlikely."
--
Check out http://groups.yahoo.com/group/californiadisasters/
Read our blog at http://eclecticarcania.blogspot.com/
Visit me on Facebook at http://www.facebook.com/derkimster
__._,_.___
No comments:
Post a Comment