Irrigation-based groundwater pumping in California could potentially stress the San Andreas fault and increase the risk of earthquakes in the region.
Researchers looked at GPS readings to determine that San Joaquin Valley floor is sinking as a result of groundwater depletion, raising the surrounding mountains. This phenomenon could be putting stress on the San Andreas Fault, the Associated Press reported.
"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, told the Associated Press.
The finding suggests that irrigation could be putting Californians at risk of experiencing more earthquakes.
"These results suggest that human activity may give rise to a gradual increase in the rate of earthquake occurrence," the Nature study said, the Los Angeles Times reported.
Groundwater is heavy so when it is present it weighs down the Earth, but when removed the ground springs back up.
"It reduces the forces that are keeping the fault clamped together - leading to more small earthquakes during dry periods of time," Colin B. Amos, assistant professor of geology at Western Washington University, the lead author of the study told the Associated Press. "During wet periods of time when the fault is loaded down, the forces that are keeping the fault clamped down are greater. It inhibits the sliding of the fault."
The amount of groundwater lost in the Central valley through irrigation practices is believed to be enough to fill up Lake Tahoe. A predicted drought could deplete even more groundwater. The upward movement of the land is believed to have the ability to trigger small earthquakes, but researchers are unsure of whether or not it can affect the risk of larger events.
"These earthquakes are likely to occur no matter what humans do," Amos said.
