Stress Meter Detects Quake Hours In Advance

Berkeley, CA (AHN) - The measurement of stress in rocks deep in California's San Andreas Fault has shown promise in predicting earthquakes after the method was able to detect ground vibration several hours in advance.

Based on the test of a seismic stress meter set up at the San Andreas Fault Observatory at Depth (SAFOD) near Parkfield, CA, the instrument detected a distinct change in the rock 10 hours before a magnitude 3 earthquake occurred on Dec. 24, 2005. The same instrument measured similar signals two hours before a magnitude 1 temblor occurred five days later.

Scientists from Rice University in Texas, the Carnegie Institution in Washington, and the U.S. Department of Energy's Lawrence Berkeley National Laboratory, conducted the experiment. Results of the test were published in the Thursday issue of the science journal Nature.

In the experiment, scientists suspended a stack of donut-shaped piezoelectric ceramic cylinders in water inside one borehole of the SAFOD at a depth of more than half a mile or one kilometer. Like a stereo speaker, the cylinders produce seismic signals when voltage is applied. When the stack expands, the cylinders exert pressure on the water, which exerts pressure on the rock.

The scientists also set up an accelerometer at the same depth in an adjacent borehole. The device measures the travel time of the rhythmic signals produced by the device in the other borehole as the signal travels through the rock.

The method and instruments are currently being tested in quake zones in China and Japan, said seismologist Fenglin Niu, lead author of the study.