Water pumping elevates Central Valley, increasing earthquake odds

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In a dire drought like this one, most people aren’t worried about the connection between groundwater pumping and seismicity. Yet in addition to the slew of other ensuing problems, over pumping the Central Valley’s groundwater basic might lead to more earthquakes, according to Roland Burgmann, a University of California, Berkeley seismologist and co-author of a study released last week in Nature. The change is slight, he said. “I don’t think the earthquake connection is likely to be a real concern in a practical sense,” Burgmann said. The number of smaller earthquakes along the San Andreas Fault near Parkfield in southern California increases in the late summer and early fall, the researchers said. This coincides with the peak of groundwater pumping, which increases the elevation of the Central Valley, Burgmann said. He likened the phenomena to removing a large object from a bed. The springs rise, releasing pent-up tension, and increasing the probability the fault will start to slide. Conversely, snow and rain pushes down the Sierra and the Coast Ranges in the winter and spring. Burgmann’s team analyzed GPS data from several east-to-west transcripts in southern California. They discovered that water, not plate tectonics, is the major driver of elevation change in the region, he said. “I think in the end, it wasn’t surprising. It seems to make so much sense,” Burgmann said. The southern Sierra is rising one to three millimeters a year, which might not sound significant, but adds up over time, Burgmann said. “The goal was to demonstrate the water connection is the correct connection,” Burgmann said. Evidence that water drives the annual elevations changes is strong, but it’s a bit trickier to tease apart the variety of other factors that affect long-term elevation, Burgmann. The lead author is Colin Amos, now with Western Washington University.