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Tides in Earth's crust trigger small, deep quakes

Study of one portion of the San Andreas fault finds that just a little added stress makes a quake more likely

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4:47pm, December 23, 2009

The subtle changes in stress caused by tides in Earth’s crust can trigger small, deep quakes along a seismically active portion of California’s San Andreas fault, a new analysis suggests.

The same forces of attraction that cause ocean tides also cause tides in Earth’s rocks, says Amanda Thomas, a seismologist at the University of California, Berkeley. And although the continual variations in rock stress associated with those tides are minuscule, they apparently are big enough to trigger small tremors along some faults, Thomas and Berkeley colleagues Robert M. Nadeau and Roland Bürgmann report in the Dec. 24/31 Nature.

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