Excessive use of groundwater in California's Central Valley can put additional stress on the San Andreas Fault and can give rise to more earthquakes in the region, according to a joint study by the Western Washington University, University of Ottawa, University of Nevada, Reno and the University of California, Berkeley.
Groundwater levels have reduced by more than 300 feet in some areas of the San Joaquin Valley. Over the last 150 years, about 160 cubic kilometres or 40 cubic miles of groundwater in the Valley has been drawn either for irrigation or has evaporated.
This gradual depletion has released more than 176 billion tons of weight from the Earth's crust, causing the crust to bounce upward and raising the mountains that border the valley - the Sierra Nevada to the east and the Coastal Range to the west.
The changes in pressure and flexing of regions could trigger more minor earthquakes.
"It reduces the forces that are keeping the fault clamped together - leading to more minor earthquakes during dry periods," said Colin B. Amos, assistant professor of geology at the Western Washington University and the lead author of the study. "During wet periods - when the fault is loaded down - the forces that are keeping the fault clamped down are greater. It inhibits the sliding of the fault," Russia Today reports.
Researchers said that the changes in pressure were previously believed to be caused by rainfall or hydrologic activities.
"Other studies have shown that the San Andreas Fault is sensitive to small-scale changes in stress. These changes appear to control the timing of small earthquakes on portions of the fault, leading to more small earthquakes during dryer periods of the year," said Amos, Tech Times reports.
Researchers said that the relationship between earthquakes and groundwater has not been discovered for the first time. A 2011 study found that an earthquake of 5.1 magnitude in Lorca, Spain, might have been caused by groundwater exploitation in the region.
Besides groundwater extraction, other human activities - filling up or draining large reservoirs and waste water injection from fracking operations - have also been tied to quakes.
The findings are published in the journal Nature.
