News Release 07-027
Scientists Explain Source of Tiny Tremors Emanating from Fault Zones
Tiny non-volcanic earthquakes may indicate dangerous conditions
March 15, 2007
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Tiny earthquakes called non-volcanic tremors recently discovered in fault zones from California to Japan are generated by slow-moving earthquakes that may foreshadow catastrophic events, according to scientists at Stanford University and the University of Tokyo.
In a study published in the March 15 issue of the journal Nature, seismologists say their findings may be useful in understanding potentially destructive mega-quakes of magnitude 8 or higher. The research was funded by the National Science Foundation (NSF).
"This work gives us a way to use different types of seismic activity to monitor places where large, destructive earthquakes occur," said Eva Zanzerkia, program director in NSF's Division of Earth Sciences.
Gregory Beroza, a geophysicist at Stanford and co-author of the Nature study, said that non-volcanic tremors are often accompanied by low-frequency earthquakes (LFEs)--small quakes of magnitude 1 or 2.
To date, LFEs have been found primarily in subduction zones--seismically active faults where two tectonic plates meet and one plate constantly dives beneath the other. A recent example was the devastating 2004 earthquake near Sumatra, where a magnitude 9.2 quake triggered powerful tsunamis that killed more than 200,000 people.
Recent studies suggest that these giant quakes, which form at relatively shallow depths, are preceded by a series of much deeper events called slow (or silent) earthquakes, which displace the ground without shaking it. A slow earthquake can last days, months or years without being felt at the surface.
But detecting slow quakes is a difficult task, Beroza said. That's one reason why seismologists were particularly excited by the recent discovery of LFEs in the subduction zone near Shikoku, Japan.
The insight may open new avenues of research for predicting earthquake hazards by using LFEs as indictors, said David Shelly, also a Stanford scientist. "This could lead to an improved ability to forecast a major earthquake in these regions."
Seismologist Satoshi Ide of the University of Tokyo is the third co-author on the Nature study.
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