Depletion Of California’s Groundwater Is Triggering Earthquakes, Study Finds

CREDIT: AP Photo/Marcio Jose Sanchez

The dry bed of the Stevens Creek Reservoir is seen in March in Cupertino, Calif.

California’s record-breaking drought is helping spark wildfires and drying up farmland, but it appears to be having another unforeseen consequence: increasing the state’s chance of earthquakes.

A study published in the journal Nature on Wednesday found that the depletion of groundwater in California’s San Joaquin Valley is putting pressure on the San Andreas Fault, which could be increasing the risk of earthquakes in the region. Colin Amos, Assistant Professor at Western Washington University and lead author of the study, said he was “absolutely” surprised by the results of the study — the researchers hadn’t started out looking into whether groundwater removal affected earthquake activity, but when they looked at the GPS data for the region, they noticed tectonic activity was clustered around the region where groundwater was being lost.

“The upward portion of the earth behaves elastically — if you push on it and remove that force, it snaps back,” Amos said. He said that the the rocks underneath California are loaded by the weight of groundwater, and if that groundwater is removed, the rocks rise slightly. Because there are faults in those rocks, the faults experience a stress change while the rocks shift upwards. Amos and his team hypothesize that this change in stress could be responsible for changes in earthquake activity in the region.

Amos said linking earthquakes to groundwater removal isn’t unprecedented — one study found a 2011 magnitude 5.1 earthquake in Lorca, Spain may have been triggered by groundwater extraction in the region. Other human activities have been tied to quakes — Amos said filling up or draining large reservoirs can also trigger fault activity, and scientists have linked wastewater injection from fracking operations to clusters of small earthquakes in regions that previously had had little tectonic activity.

So far, the uplift and seismic activity that can be partially attributed to groundwater approval is minor. However, the study states, the activity puts more stress on the San Andreas fault, which could bring the fault closer to failure, in turn triggering a much larger earthquake.

The study also points to another problem in California: the sheer quantity of groundwater that’s being removed from the San Joaquin Valley, a quantity Amos called “staggering.” Over the last 150 years, about 160 cubic kilometers — about 40 cubic miles — of groundwater in the Central Valley has has been pumped out, used for irrigation or has evaporated. The study highlights this practice of removing groundwater as something that could become even more resource-consuming if California’s drought continues.

“Future scenarios for groundwater in California suggest increasing demand for agricultural, urban and environmental use,” the study reads. “Climate change will probably exacerbate the stress on this resource through altered precipitation patterns, more frequent droughts, earlier snowmelt, larger floods, and increasing temperatures and evapotranspiration.”

California’s drought has been thrown into sharp relief over the last few days. In Southern California, nine fires forced the evacuation of tens of thousands of residents this week, and on Wednesday, a fire in San Diego County forced the evacuation of a nuclear plant. The state has also struggled with soaring temperatures — San Francisco, Mountain View, and Monterey have all set or tied heat records already this spring.