GPS stations atop the Sierra Nevada and Coast Ranges revealed a steady rise—10 millimeters in the past seven years—of the mountains' peaks. A study published in Nature yesterday credits the rise to the current drought and removal of 7.5 cubic miles of groundwater from the San Joaquin Valley between 2003 and 2010.
Studies in earth and planetary sciences from the University of California, Berkeley suggest that such levels of deep-earth stress heighten the risk for microquakes on the San Andreas Fault and could trigger much larger seismic events.
The most recent study's co-author, Berkeley's Roland Burgmann, says that millimeter fluctuations in the mountains could provide "that extra push to get a fault to fail."
According to his study, water weight removed from the area during the past 150 years (equivalent to about 40 cubic miles) caused the Sierra Nevada's underlying crust to "rebound" half a foot. The inverse is true as well. During torrential downpours—usually during the winter—the mountain range's crust soaks up water and pushes down its peaks some three millimeters, the study details.
The Sierra Nevada's movements were previously attributed to tectonic activity until this study was published. Now we must ask, if the drought continues, will peak activity up seismic activity along the San Andreas Fault?
Burgmann thinks so. "Water changes ultimately affect the deeper earth too," he says.