Manmade Earthquakes: Geothermal Power Production Rocks California

Can earthquakes be manmade? It turns out they can, and a certain geothermal power facility may be causing them. Scientists have discovered that the production of geothermal power, which involves pumping water into and out of an underground reservoir, may be causing seismic activity around the Salton Sea Geothermal Field in California.

Scientists have found that certain activities can cause manmade earthquakes in the past. For example, researchers have discovered that storing pressurized CO2 underground to lock up climate change-inducing greenhouse gases could potentially cause earthquakes. In addition, they've found that wastewater injections, associated with the practice of hydraulic fracturing, can also cause small seismic events.

In order to examine if activities around the Salton Sea Geothermal Field may be causing seismic activity, researchers studied earthquake records for the region from 1981 to 2012. They then compared this earthquake activity with production data for the geothermal power plant, including records of fluid injection and extraction. Since this power plant is a flash-steam facility, it pulls hot water out of the ground, flashes it to steam to run turbines and then recaptures as much water as possible for injection back into the ground.

So what did they find? During relatively low-level geothermal operations before 1986, the rate of earthquakes in the area was also low. Yet as these operations expanded, earthquake activity climbed. This seemed to indicate that, in fact, the operations were having an impact on seismicity.

"We found a good correlation between seismicity and net extraction," said Emily Brodsky, a geophysicist at the University of California, in a news release. "The correlation was even better when we used a combination of all the information we had on fluid injection and net extraction. The seismicity is clearly tracking the changes in fluid volume on the ground."

Fortunately, these induced earthquakes are small. Yet the key question is what is the biggest earthquake that could occur in the area. So far, the largest earthquake that's occurred over the 30-year study period has been a magnitude 5.1 quake. That said, the nearby San Andreas fault has a much larger capacity for massive quakes, capable of unleashing ones that are at least magnitude 8.

"It's hard to draw a direct line from the geothermal field to effects on the San Andreas fault, but it seems plausible that they could interact," said Brodsky.

With current underground activities, it's more important than ever to understand exactly how they can affect seismic activity. This latest study shows a little more about the potential for manmade earthquakes, which could allow us to avoid them in the future.

The findings are published in the journal Science.