April 15, 2006
Predicting Earthquakes Still Elusive
LOS ANGELES -- The monster earthquake that turned San Francisco into smoky rubble a century ago also gave rise to seismology, but scientists still can't predict when the next Big One will pop.
Several mysteries must be unraveled before seismologists can forecast a potential killer shock with the precision that meteorologists have in pinpointing a hurricane's strength days beforehand.
At the heart of the problem are two fundamental questions: How does an earthquake begin? What causes it to stop?
"If we can find a magic signal, some telltale sign, then maybe we'll know when an earthquake is coming," said Tom Jordan, the director of the Southern California Earthquake Center in Los Angeles.
Before 1906, science had only faint ideas of the forces behind temblors. Three days after San Francisco's powerful jolt tore open the Earth's surface along a 300-mile stretch of the 800-mile-long San Andreas fault, scientists set out to map the fault, which cuts through California like a scar.
Researchers now know that earthquakes are caused by the constant grinding of continental plates, which builds up strain in the Earth's crust. At some point, the plates can get stuck at a boundary called a fault and snap, unleashing the pent-up energy in sudden, earthshaking bursts.
Several million earthquakes occur worldwide each year, according to the U.S. Geological Survey; many go undetected because they either hit very remote areas or are too minor to be felt.
In the 1970s, there was buzz that scientists were close to being able to predict quakes. Some believed the answer lay in measuring the speed at which sound rippled through rocks, others in analyzing animals' reactions to sudden ground movement.
The excitement soon fizzled. Forecasts have never proven reliable.
Still, several studies are under way to determine whether earthquakes possess certain predictable behavior and characteristics.
Seismologists this year plan to install instruments into an active section of the San Andreas in central California to observe what happens during stress buildup in the ground. By monitoring the fault, scientists hope to catch a birthing quake.
Another project by the Southern California Earthquake Center, a consortium of research universities, will use a $1.2 million grant to set strict standards for earthquake prediction experiments.
Scientists have been keeping a watchful eye on the southern segment of the San Andreas fault near San Bernardino, which is overdue for a major quake. The last time it snapped was in 1690, producing an estimated 7.7-magnitude quake.
Short of being able to foresee the next San Francisco-like calamity, scientists have focused on buffering the damaging effects of quakes and have made significant strides in taking the Earth's pulse.
Within minutes of a temblor, the USGS posts maps on the Internet showing its epicenter and where the most severe shaking occurred. Scientists constantly keep tabs on seismic strain near sections of faults that haven't ruptured in decades.
They also are working on long-term forecasts that calculate the likelihood of a quake based on historical geologic evidence, in order to help prioritize which buildings and freeways to reinforce.
"Even if we can predict earthquakes," said Mary Lou Zoback of the USGS in Menlo Park, "that won't prevent buildings from falling down."
On the Net:
1906 anniversary page: http://1906centennial.org
U.S. Geological Survey: http://www.usgs.gov
Southern California Earthquake Center: http://www.scec.org
Caltech Seismological Laboratory: http://www.seismolab.caltech.edu