San Andreas Fault
LOS ANGELES -- A spike in underground rumblings on a section of the San Andreas fault has seismologists on edge. It's the same section of the fault that produced a magnitude 7.8 earthquake in 1857.
Experts aren't sure if the vibrations are an indication of an imminent earthquake. They do say, however, that deep tremors mean underground stress which could raise the risk of a major quake.
Researchers at the University of California, Berkeley, monitored seismic activity on the fault's central section between July 2001 and February 2009 and recorded more than 2,000 tremors. The tremors lasted mere minutes to nearly half an hour.
Unlike earthquakes, tremors occur deeper below the surface and the shaking lasts longer.
During the study period, two strong earthquakes hit - a magnitude-6.5 in 2003 and a magnitude-6.0 in Parkfield a year later. Scientists noticed the frequency of the tremors doubled after the 2003 quake and jumped six-fold after 2004.
Tremor episodes continue today although the frequency of tremors has declined since 2004. Scientists are still concerned because the tremors are taking place at a level twice that of those that occurred before the 2003 quake. The team also recorded unusually strong rumblings days before the 2004 temblor.
Predicting large quakes with precision is the elusive Holy Grail. Scientists have only been able to calculate probabilities for quakes in certain areas by analyzing a time line of ruptures and calculating the amount of stress building on a fault. The latest study may potentially inch us closer to having an actual predictor, scientists said.
Results of the research appear in Friday's issue of the journal Science. The work was funded by the U.S. Geological Survey and National Science Foundation.
Experts aren't sure if the vibrations are an indication of an imminent earthquake. They do say, however, that deep tremors mean underground stress which could raise the risk of a major quake.
Researchers at the University of California, Berkeley, monitored seismic activity on the fault's central section between July 2001 and February 2009 and recorded more than 2,000 tremors. The tremors lasted mere minutes to nearly half an hour.
Unlike earthquakes, tremors occur deeper below the surface and the shaking lasts longer.
During the study period, two strong earthquakes hit - a magnitude-6.5 in 2003 and a magnitude-6.0 in Parkfield a year later. Scientists noticed the frequency of the tremors doubled after the 2003 quake and jumped six-fold after 2004.
Tremor episodes continue today although the frequency of tremors has declined since 2004. Scientists are still concerned because the tremors are taking place at a level twice that of those that occurred before the 2003 quake. The team also recorded unusually strong rumblings days before the 2004 temblor.
Predicting large quakes with precision is the elusive Holy Grail. Scientists have only been able to calculate probabilities for quakes in certain areas by analyzing a time line of ruptures and calculating the amount of stress building on a fault. The latest study may potentially inch us closer to having an actual predictor, scientists said.
Results of the research appear in Friday's issue of the journal Science. The work was funded by the U.S. Geological Survey and National Science Foundation.
