Study links earthquake frequency to groundwater pumping

Earthquake
Bill Hammond/Courtesy

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A UC Berkeley professor joined forces with fellow seismologists to release a groundbreaking study Wednesday that links a rise in earthquake frequency in California’s Central Valley to the pumping of groundwater in the area.

Roland Burgmann, a campus professor of earth and planetary science who contributed to the research, said observations were conducted by measuring the rate of mountain growth in the San Joaquin Valley compared to other parts of California. The study claims fluctuations in rock height are generally evened by the San Andreas Fault but that superficial flux “brings the fault closer to failure” and might result in more microquakes.

“We see how Earth flexes in response to a changing water load,” Burgmann said. “In the valley, we see a loss of water because of ground pumping.”

The study indicates fluctuations in the Earth’s crust are correlated with human industrial practices. It found that these fluctuations, as indicated by mountain growth, lead to small-magnitude earthquakes.

“Humans have caused the earth to go up a little around San Joaquin Valley,” said Thomas Holzer, a research geologist with the U.S. Geological Survey’s earthquake hazard team and Burgmann’s colleague.
Holzer added that groundwater pumping in the area resulted in a permanent load reduction on the Earth’s crust.

According to Burgmann, the loss of groundwater in the Central Valley is also a result of both drought conditions and water pumping and irrigation.

Research was led by Colin Amos and Pascal Audet, both former UC Berkeley postdoctoral fellows and now researchers at Western Washington University and the University of Ottawa, respectively. The studies were conducted with vertical global positioning satellite systems. Upon analysis of GPS data, the researchers postulated that the change in water-weight pressure may result in more small-magnitude earthquakes because removed water lets the Earth’s crust move slightly.

“Small earthquakes don’t seem important, but they can be important, because studies suggest that large earthquakes are preceded by small earthquakes,” Holzer said. “But the reasoning in my proposal is (that) every small earthquake has a one-in-a-million chance of turning into something very large.”

Burgmann said the effect is similar to natural seasonal changes, when depleted water levels during summer months cause the Earth’s crust to rise while winter rains and snow weigh it down. He explained that although the effects are only millimeter changes, even the slightest movement can have profound consequences.

Still, not all scientists think the research indicates dire consequences.

“I’m not terribly concerned about larger earthquakes,” said Fred Pollitz, a supervisory research geophysicist with the USGS. “It’s really speculative to think that this might trigger earthquakes.”

Contact Zoe Kleinfeld at [email protected] and follow her on Twitter @zoekleinfeld.