Under pressure By Jeff Hecht Subterranean water may trigger repeated quakes. Water that is squeezed out of rocks could explain deep earthquakes that recur more than a decade apart, geologists say. Researchers speculated that the fluid might have come from water-containing minerals far below the surface.
Many minerals incorporate water into their crystalline matrices.
At great depths, the Earth's internal heat makes them unstable, causing them to take on a different solid form and release the fluid. The metamorphosis weakens the rock because the water it produces increases the total volume, pushing the fabric of the rock apart. The earlier models assumed that there are no temperature variations within the rock. But Ague points out that reactions don't normally occur without such variations. The heat could come from friction on moving faults, or nearby magma.