A new study has found that continuous groundwater pumping in California's Central Valley will likely cause an earthquake in the future.
Researchers have discovered that winter rains followed by summer groundwater pumping are causing the Sierra Nevada and Coast Mountain Ranges to rise and fall a few millimeters every year. They identified groundwater pumping as the cause of persistent diminution in the Central Valley aquifer, which also raises the ranges by the same amount simultaneously. Over the past 150 years, the ranges have increased by up to 15 centimeters, or 6 inches.
Although the seasonal changes in the Central Valley aquifer have not been proven to be linked to earthquakes yet, studies have shown that similar levels of periodic stress such as those from sun and moon movement have increased the number of microquakes on the San Andreas Fault.
Roland Bürgmann, a geologist and co-author of the study from the University of California, Berkeley, explained in a press release: "The stress is very small, much less than you need to build up stress on a fault leading to an earthquake, but in some circumstances such small stress changes can be the straw that breaks the camel's back. It could just give that extra push to get a fault to fail."
Researchers studied California and Nevada GPS data from 2007 to 2010 to measure the changes in the Central Valley acquifer. Their analysis revealed that groundwater pumping has been happening in Central Valley for more than 150 years, transforming the Tulara Lake, which was formerly a marsh, into agricultural fields.
"When humans deplete groundwater, the amount of mass or material in Earth's crust is reduced," said Maggie Benoit, a program director in NSF, in a press release. "That disrupts Earth's force balances, causing uplift of nearby mountains and reducing a force that helps keep the San Andreas fault from slipping."
Further details of the study can be read on the May 14 issue of Nature.
