Massive Chile Quake May Have Set Off California Shaking

Feb 1, 2011 11:11 AM ET

By Charles Q. Choi, Our Amazing Planet Contributor

The massive earthquake that rocked Chile in 2010 could have triggered a swarm of smaller quakes thousands of miles away in California, researchers suggest.

The magnitude 8.8 earthquake that hit Chile last year struck just offshore of areas holding 80 percent of the country's population. The quake killed at least 521 people, injured about 12,000 more and damaged or destroyed at least 370,000 houses.

Now it turns out Chile might not have been the only place this quake affected.

"We now know that a very large earthquake like the 2004 Sumatra earthquake and the 2010 Chile quake can trigger seismic activity potentially at anywhere within the Earth, because the seismic waves from such major earthquakes are large enough to circle the entire globe," researcher Zhigang Peng, a seismologist at the Georgia Institute of Technology in Atlanta, told OurAmazingPlanet.

Earthquakes 'talk'

Peng and his colleagues suggest the Chilean quake triggered four earthquakes with magnitudes of 2 or higher that shook California, with the largest of the group being a magnitude 3.5 quake that rattled the Coso Volcanic Field about 5,730 miles (9,220 kilometers) away, where several geothermal power plants are located. Although this area is one of the most seismically active regions in California and often plagued by small quakes, when the researchers estimated the chance of an earthquake swarm occurring there immediately following the Chilean earthquake, their calculations suggest there was a more than 99 percent chance the two seismic events were probably connected.

The seismologists also detected a cluster of deep tremors along the Parkfield-Cholame section of the San Andreas Fault that also appeared to be influenced by the Chilean quake about 5,820 miles (9,360 km) away. That section of the San Andreas was the site of possibly the largest quake on that fault in the last few centuries, the 1857 Fort Tejon earthquake, a magnitude 7.9 temblor.

So how might one quake help set off these others? The researchers suggest the Chilean quake could have sent off so-called "love waves" — horizontal surface movement that would have traveled from their epicenter all the way to California, pushing already stressed faults over the edge.

"Earthquakes talk to each other," Peng said. "Many scientists have found that when a large earthquake occurs, it will trigger numerous earthquakes, mostly around the previous one, which are known as aftershocks. Some of them could be potentially dangerous."

But whether or not large earthquakes can trigger other large earthquakes from far away is still an unanswered question.

"So far we have found much evidence that large earthquakes could trigger small earthquakes at long-range distances," Peng said. "We have yet to see a damaging earthquake triggered at very large distances."

Seeds of earthquakes

One might also ask if the small tremors these distant quakes set off might relieve pressure on a fault, thus preventing or delaying larger quakes in the future. However, "since most of triggered earthquakes are small, then the built-up pressure in other faults are not relieved at all," Peng said. "However, it is possible that those triggered earthquakes could continue for a while, and may even lead to large earthquakes at later times."

These findings might help scientists better understand how the seeds of earthquakes are planted, and how quakes interact with each other across long distances.

"We can now calculate the stress perturbations from distant earthquakes — such information is crucial to understand how earthquakes are triggered," Peng said. "We are still far from applying it to accurately predicting earthquakes. However, our study, together with others, could be used to improve our understanding of earthquake physics."

"We can now calculate the stress perturbations from distant earthquakes," said researcher David Hill at the U.S. Geological Survey at Menlo Park, Calif. "Such information is crucial to understand how earthquakes are triggered. We are still far from applying it to accurately predicting earthquakes. However, our study, together with others, could be used to improve our understanding of earthquake physics."

Slow earthquakes

These findings might shed light on enigmatic "slow earthquakes" — ones that happen over the course of anywhere from hours to months — that scientists know little about. These slow quakes can involve deep tremors like those the Chilean quake triggered in the San Andreas.

Future research could shed light on connections between slow earthquakes and regular ones, said seismologist John Vidale, director of the Pacific Northwest Seismic Network, who did not take part in this study.

The researchers are now systematically analyzing both Coso and Parkfield to find out how many distant large earthquakes might have triggered activity in each region over the past 10 years and why.

"In addition, we are examining global seismic data sets to find out if great earthquakes like Sumatra and Chile could affect the occurrence of moderate to large earthquake activity globally," Peng said. "This would help to improve our understanding of how large earthquakes interact with each other."

Peng, Hill and their colleagues detailed their findings Dec. 31 in the journal Geophysical Research Letters.

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