Geothermal power plants on the southern shore of southern California’s Salton Sea are causing earthquakes in the area, just 12 miles from the San Andreas Fault, according to a newly published peer-reviewed study. The study could not determine whether the geothermal power plants may one day trigger a larger earthquake along the San Andreas Fault.
30-Year Study Finds Connection
The study, published July 11 in Science, analyzed 30 years of earthquake data since the geothermal power plants began operation on the southern edge of the Salton Sea in 1982. The study found earthquake activity rose in conjunction with geothermal power production. From 1981 through 2012, more than 10,000 earthquakes above magnitude 1.75 occurred in the area of the geothermal power pants. The largest quake measured 5.1 on the Richter scale.
The lead author of the study, Emily Brodsky, said it was plausible geothermal power production could trigger a large San Andreas earthquake.
Geothermal power projects extract extremely hot water from deep beneath the earth’s surface and use it to produce steam to drive electricity-producing turbines. Power plant operators inject the remaining brine back underground.
Assessing the Risks
William Ellsworth, a geophysicist with the U.S. Geological Survey office in Menlo Park, says it is long-settled science that geothermal energy production can cause earthquakes. In fact, Ellsworth said, the earthquakes are a necessary component of continuing geothermal power production. Without the small earthquakes, the geothermal field would close up.
Ellsworth said large earthquakes can sometimes begin on smaller, nearby faults and then jump to the main fault. He said this is how the 2002 magnitude 7.9 Denali Fault earthquake began in Alaska. The initiating event in that case was sizeable, over magnitude 6, he said.
“Could much smaller earthquakes off of the San Andreas fault trigger a large San Andreas Fault earthquake? Yes. How likely is this to happen? This is an active area of research,” said Ellsworth. “However, it is very unlikely that any particular earthquake will trigger ‘the big one,’ as tens of thousands of them happen in California every year and the last major San Andreas Fault earthquake was over 100 years ago in 1906.”
Ellsworth said studies of geothermal power plants along the San Andreas Fault in northern California also show the geothermal power plants trigger earthquakes, but none of the earthquakes triggered a larger quake along the San Andreas Fault.
“Studies of geothermally induced earthquakes at The Geysers in northern California do not show any evidence for triggering of earthquakes on nearby faults of the San Andreas Fault system,” Ellsworth said.
Alyssa Carducci ([email protected]) writes from Tampa, Florida.
Brodsky, E., “Anthropogenic Seismicity Rates and Operational Parameters at the Salton Sea Geothermal Field,” Science, July 11, 2013, http://www.sciencemag.org/content/341/6145/543.abstract