Mysterious Tremors Along San Andreas Fault

Gemeos · 07-10-2009, 11:54 AM

http://news.sky.com/skynews/Home/Wor..._Andreas_Fault

8:45pm UK, Thursday July 09, 2009
Scientists are reporting a spike in underground rumblings along a section of California's San Andreas Fault that produced a massive earthquake in 1857.

Some experts think the deep tremors may indicate tension is building fast - sparking an increased 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.

During that period, two strong earthquakes hit - a 6.5-magnitude in 2003, and a 6.0-magnitude a year later.

They noticed the frequency of the tremors doubled after the 2003 quake and jumped six-fold after 2004.

What these mysterious vibrations say about future earthquakes in California is far from certain.

But even though the frequency of tremors have recently declined, scientists are concerned because they are still at a level twice as high as before the 2003 quake.

The research - printed in this week's issue of the journal Science - was funded by the US Geological Survey and National Science Foundation.

"The fact that the tremors haven't gone down means the time to the next earthquake may come sooner," said Berkeley seismologist and lead researcher Robert Nadeau.

He first discovered tremors deep in the San Andreas Fault in 2005.

Before that, the phenomenon was only thought to occur in Earth's subduction zones, where one tectonic plate dives beneath another.

USGS seismologist Susan Hough said the research was intriguing, but it was too soon to know what it means.

"We don't have enough data to know what the fault is doing in the long term," she added.

07-10-2009, 11:54 AM	#1
Gemeos Avalon Senior Member Join Date: Jan 2009 Location: Portugal Posts: 303	Mysterious Tremors Along San Andreas Fault http://news.sky.com/skynews/Home/Wor..._Andreas_Fault 8:45pm UK, Thursday July 09, 2009 Scientists are reporting a spike in underground rumblings along a section of California's San Andreas Fault that produced a massive earthquake in 1857. Some experts think the deep tremors may indicate tension is building fast - sparking an increased 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. During that period, two strong earthquakes hit - a 6.5-magnitude in 2003, and a 6.0-magnitude a year later. They noticed the frequency of the tremors doubled after the 2003 quake and jumped six-fold after 2004. What these mysterious vibrations say about future earthquakes in California is far from certain. But even though the frequency of tremors have recently declined, scientists are concerned because they are still at a level twice as high as before the 2003 quake. The research - printed in this week's issue of the journal Science - was funded by the US Geological Survey and National Science Foundation. "The fact that the tremors haven't gone down means the time to the next earthquake may come sooner," said Berkeley seismologist and lead researcher Robert Nadeau. He first discovered tremors deep in the San Andreas Fault in 2005. Before that, the phenomenon was only thought to occur in Earth's subduction zones, where one tectonic plate dives beneath another. USGS seismologist Susan Hough said the research was intriguing, but it was too soon to know what it means. "We don't have enough data to know what the fault is doing in the long term," she added.