Excessive use of groundwater for irrigation in the Central Valley may be to blame for several small earthquakes.
A new study finds that the sinking water table has caused parts of the San Joaquin Valley floor to sink over the last several decades. This then causes stress to the San Andreas Fault running through California.
Scientists say these findings are new, but living in California, the threat of earthquakes remains the same.
While small earthquakes happen often, it's unclear what is the potential for a large earthquake because of excessive groundwater pumping.
In this drought year, many farmers are pumping underground water to irrigate their crops.
Aric Olson, president of Jain Irrigation, installs drip and micro irrigation for many farmers. He says, this past year, there's been a substantial increase in groundwater pumping.
"Just to keep the permanent crops alive, you're going to have to grow or pump that much more water--could be 35 percent more," Olson says.
But scientists say this kind of excessive pumping of groundwater is stressing the San Andreas Fault, which runs roughly the length of California.
The study finds that in the past 100 years, the Central Valley has lost an amount of ground water equal to the volume of Lake Tahoe.
"We've removed so much groundwater from the San Joaquin Valley that we've actually unloaded the earth's crust," says Thomas Holzer, a geologist with the United States Geological Survey (USGS) in Menlo Park.
Going on three dry years, scientists say more water is being tapped faster than it can be replaced.
The study suggests that this kind of human activity is causing the earth to move.
While the observations are new, scientists say the threat of earthquakes isn't.
"So it's basically unclamping the fault a little bit, but the amount is so small that it's not likely to have a terribly large effect," Holzer says.
Scientists have long been warning of the potential for a large and destructive earthquake to hit the state. They say in California, it's always a good idea to be prepared with supplies and know what to do if a big earthquake hits.