Link between oil drilling and California earthquakes discovered at San Ardo.

California has lots of oil drilling and many earthquakes. Those two things were thought to be unrelated. 

As scientists discovered that oil operations caused earthquakes in Texas and Oklahoma and elsewhere, they could not find any such link in California. 

Now, two earthquake researchers who studied seismological activity near the San Ardo oil fields in south Monterey County say that the industry’s injection of wastewater into the ground has likely been triggering small earthquakes for decades. 

Their work was funded by the U.S. Department of Energy and published on Nov. 11 in the academic journal Seismological Research Letters. The authors are Thomas H. W. Goebel from the University of Memphis and Manoochehr Shirzaei from Virginia Tech. 

They chose San Ardo because the oil fields are located only 22 miles from the San Andreas Fault, and local oil operators pump waste fluid into the ground near seismically active faults. 

After analyzing data from 40 years of drilling at San Ardo, they found a high degree of correlation between fluid injection and earthquakes. According to the pattern that emerged, the 1,735 seismic events in the study area appeared in clusters near injection wells. In other words, while California is prone to earthquakes, it is very unlikely that tremors recorded would have happened where they did if not for the added stress on the tectonic faults.

The earthquakes caused by industrial fluid injection tend to be small and harmless, but on occasion, they have been powerful enough to damage buildings and wells. 

Short of shutting down oil fields, there are ways to reduce the likelihood of human-caused earthquakes. Researchers Goebel and Shirzaei provide three measures: reducing the amount of waste fluid, injecting away from certain geologic formations, and avoiding deep tectonic faults. 

To read more about this discovery, check out this article written in ordinary English by one of the researchers.