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LOS ANGELES — Excessive groundwater pumping for irrigation in California’s agricultural belt can stress the San Andreas Fault, potentially increasing the risk of future small earthquakes, a new study suggests.
GPS readings found parts of the San Joaquin Valley floor have been sinking for decades through groundwater depletion while the surrounding mountains are being uplifted. This motion produces slight stress changes on the San Andreas and neighboring faults.
“The magnitude of these stress changes is exceedingly small compared to the stresses relieved during a large earthquake,” lead researcher Colin Amos, a geologist at Western Washington University, said in an email.
The findings were released Wednesday by the journal Nature.
The study suggests that human activities “can cause significant unclamping of the nearby San Andreas Fault system” through flexing of the Earth’s crust and upper mantle
Inner Earth May Hold More Water Than the Seas
Based on what they witnessed in their lab, the researchers concluded that more water probably exists deep within the Earth than is present on Earth's surface—as much as five times more.
"Our results suggest that the lower mantle can potentially store considerable amounts of water," said Motohiko Murakami of the Tokyo Institute of Technology, where the experiments were conducted.
"The presence of water in the crystal structure of [deep-Earth] minerals would be expected to soften the minerals and change their flow behavior," he added. That, in turn, could affect how the innards of the planet mix and shift over time, and could indirectly affect conditions and forces near the surface, such as plate tectonics.
Trees Humidify Air
Among plants, trees are by far the most effective evapo-transpirers. Complementing oceans, trees form the other half of the planet-wide system known as the rain or water cycle. A typical tree breathes out 250 to 400 or more gallons of water per day through the amazingly large surface area of its leaves (an acre of forest can contain well over 1,000 acres of leaf surface area).
It's almost impossible to overstate trees' ability to humidify air and thereby maintain the rain cycle far from oceans. While some rainfall evaporates directly from the ground and from small plants (this can amount to most of a light rain), evapotranspiration by trees accounts for the great majority of inland rain. ...
No Trees, No Rain