It is just a few months short of the 20th anniversary of Loma Prieta earthquake: “a major earthquake that struck the San Francisco Bay Area of California on October 17, 1989 at 5:04 p.m. local time. Caused by a slip along the San Andreas Fault, the earthquake lasted approximately 15 seconds and measured 6.9 on the moment magnitude scale.” [Wiki] I will always remember the exact moment it happened. I was at a trade show at the San Jose convention center, and everything started to shake and things came crashing down. Now I am back in the bay area for a few weeks. Is the ground going to shake?
San Francisco Chronicle reports “Mysterious tremors detected on San Andreas Fault“.
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 a year later. Scientists noticed the frequency of the tremors doubled after the 2003 quake and jumped six-fold after 2004.
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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.
“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.
Berkeley itself is situated right on top of a major fault: the Hayward Fault.