Fault Monitoring Breakthrough May Help Predict Quakes

Sept. 30, 2009 -- A breakthrough method of measuring the strength of earthquake-prone faults is shedding new light on the vast interconnectivity of quakes around the world, according to a study published in Nature.

This new development could in time help scientists predict the likelihood of earthquakes, which have most recently rocked the South Pacific.

Taka'aki Taira of the University of California, Berkeley and a team of researchers looked at small, reliable tremors along the Parkfield section of the San Andreas Fault recorded between 1987 and 2008. These "repeating earthquakes" usually occur in exactly the same spot, at regular intervals, and always have the same magnitude.

But they faltered on three occasions. In 2004, the San Andreas roared to life along the Parkfield section, rupturing with a magnitude 6.0 earthquake.

The rocks were shattered, and the repeating quakes went haywire. The team deduced that fluids were lubricating newly opened cracks and causing small tremors.

The next two anomalies occurred after major earthquakes: first following the 1992 magnitude 7.0 tremor near Landers, Calif., and then again after the devastating magnitude 9.1 Sumatra-Andaman quake that killed almost a quarter of a million people half a world away.

Each time, the repeating quakes increased in frequency but dipped in strength, indicating that rocks were slipping faster and more loosely.

In short, earthquakes from nearby as well as thousands of miles away were weakening the fault ever so slightly.

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"A change in fault strength changes the likelihood of an earthquake occurring," Taira said.

Since 2004, the team noted that there has been an increase in the number of magnitude 8.0 and greater earthquakes around the world. Though it's still too early to draw any firm conclusions, they believe the Sumatra disaster may have weakened faults and triggered temblors in many far-flung regions.

It's even possible that the quake jostled faults near the Samoan Islands enough to cause yesterday's shaker.

And while Taira said it's a long way from predicting future quakes, the team's measurements allow them to make guesses as to how much a fault has weakened. That in turn could improve estimates about when a fault is at increased risk of going critical.

"In terms of directly measuring faults strength, we still don't know how strong a fault is," Stephen Mill of the University of Bonn said. "We just know relative to last Tuesday, it's a little bit weaker now, or it's a little bit stronger now."

Still, Miller agreed that measuring such relative changes is important to gauging the likelihood of a quake. He added that being able to detect how and when pressurized water and liquid carbon dioxide (CO2) move through faults is a crucial step in understanding, and one day predicting, earthquakes.

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