When Robert Skoumal of the U.S. Geological Survey and colleagues took a closer look at some small earthquakes at the Oroville Dam in California’s Sierra Nevada foothills (see paper below), they did not find that the seismic events caused the failure of the dam's main spillway in February 2017.
Instead, their seismic sleuthing determined that the recorded swarms of tiny earthquakes came instead from fluid leaking through cracks in the main spillway that altered the pressure on the underlying rock fractures. The seismic fingerprint came from the fractures slowly opening and slamming shut, over and over. The researchers were able to detect more than 19,000 such seismic events that occurred in the 25 years before the spillway failure—and that continued after the failure. |
