Excessive groundwater withdrawal in California’s Central Valley spurred by the drought could start triggering earthquakes.
A study published in May in Nature calculates that water pumped out of the ground in the Central Valley increases crustal deformation and seismicity, thus rendering greater chances for earthquakes on the nearby San Andreas Fault.
The central valley is responsible for producing about 25% of the food consumed in the USA and now has seven million irrigated acres. Consequently, the exceptional drought conditions have prompted farmers to extract more and more water from groundwater sources and aquifers.
Takepart reported that although groundwater withdrawal in the Central Valley started increasing before 2011, the three-year-old drought has called for even more water extraction due to the dwindling surface water. During the current drought, as much as 20 cubic kilometers of Central Valley groundwater has been pumped, according to one estimate. That equates to about 12 percent of the last 150 years’ total withdrawal of groundwater.
With depleted subterranean water to hold up the earth below, the soil throughout the Central Valley is sinking. The land is dropping as much as a foot a year, in some areas causing roads and other infrastructure to crumble.
“Groundwater pumping unburdens the lithosphere,” said William Hammond, a geologist at the University of Nevada, Reno, and one of the authors of the Nature article. “When you pump that much groundwater, the load gets taken away and the landscape essentially bounces up. The Sierra Nevada is rising more quickly as a result of groundwater pumping in the Great Valley.”
Consequently, when farmers in the Central Valley start using their pumps during the hottest months, especially in drought years, they start unlocking the faults. Hammond says, “That seasonal change means loading and unloading on the lithosphere… The earth flexes up and down, and small earthquakes seem to respond to that.”
For geologists, the big fear is that we could unlock the Big One.
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