Some scientists estimate that in California's Central Valley -- one of the most productive farming regions in the world -- more than twice as much water is pumped out of the ground to irrigate crops than is returned via rain and snow.
And according to a new study by researchers at Caltech and Western Washington University, it's this imbalance that's at least partially behind the uptick in small earthquakes. As researchers explain it: the shrinking water table is further irritating the already volatile San Andreas fault, which runs the length of California and separates the Pacific and North American tectonic plates.
Geologists arrived at their conclusion after getting a better sense of the Central Valley's changing topography, thanks to new and more accurate GPS readings. Apparently, as more and more water has been sucked out of the ground to feed crops, mountain peaks have risen and valleys have shrunk.
"[Less groundwater] reduces the forces that are keeping the fault clamped together -- leading to more small earthquakes during dry periods of time," lead author Colin B. Amos, a professor of geology at Western Washington, told the Los Angeles Times.
But the irritation of the San Andreas isn't just periodic, says Caltech's Dr. Paul Lundgren, co-author of the new study published this week in the journal Nature -- there are also long-term implications.
"There is both a seasonal variation in and long term promotion of seismicity associated with the water extraction," Lundgren wrote about the new findings. "The latter may hasten the occurrence of future large earthquakes in the San Andreas fault system."
If nothing else, the study continues the movement by scientists in all fields to better understand the ways humans effect the world around them -- whether it be the climate, or tectonic plates.