Pumping water underground at geothermal power plants can lead to dangerous earthquakes even in regions not prone to tremors, according to scientists. They say that quake risk should be factored into decisions about where to site geothermal plants and other drilling rigs where water is pumped underground – for example in shale gas fracking.
Prof Emily Brodsky, who led a study of earthquakes at a geothermal power plant in California, said: “For scientists to make themselves useful in this field we need to be able to tell operators how many gallons of water they can pump into the ground in a particular location and how many earthquakes that will produce.”
It is already known that pumping large quantities of water underground can induce minor earthquakes near to geothermal power generation and fracking sites. However, the new evidence reveals the potential for much larger earthquakes, of magnitude 4 or 5, related to the weakening of pre-existing undergrounds faults through increased fluid pressure.
The water injection appears to prime cracks in the rock, making them vulnerable to triggering by tremors from earthquakes thousands of miles away. Nicholas van der Elst, the lead author on one of three studies published on Thursday in the journal Science, said: “These fluids are driving faults to their tipping point.”
Prof Brodsky said they found a clear correlation between the amount of water extracted and injected into the ground, and the number of earthquakes.
The analysis of the Californian site showed that for a net injection of 500m gallons of water into the ground per month, there is an earthquake on average every 11 days.