Earthquakes from deep within the earth are getting stronger. It's happening about 8 kilometres below the earth's surface and could be due to something called oilfield wastewater.
A research team from Virginia Tech led by Ryan Pollyea has found that earthquakes at these depths are increasing in intensity. Published in the journal Nature Communications, the team’s work has found that a super-dense liquid called oilfield wastewater is seeping deep into the sheets of the earth, causing massive pressure changes that could be increasing earthquake intensity.
“In northern Oklahoma and Southern Kansas this has been a very widespread phenomenon, we have seen it in other places throughout the US,” explains co-author Ryan Pollyea.
From the team’s data taken between 2017 to 2018, earthquakes around magnitude 2.5 - chandelier rattling territory - decreased by 35%. With the presence of the wastewater however, earthquakes around magnitude 5 increased by 150%, which is easily infrastructure-collapse territory, capable of being felt more than 300 miles in any direction.
The wastewater is a product of fracking, a common practice used by oil companies to extract trapped oil from non-permeable geologic formations. Fracking relies on pressurized water to crack rock enclosures and free the housed oil, which leads to the production of a toxic waste: an amalgamation of oil, water, and gas known as a brine. “When oil and gas are recovered a certain percentage of the product that comes out of the ground is this oilfield wastewater”, Ryan explains.
Since the wastewater is toxic to ecosystems on the earth’s surface, it is disposed of in injection wells that also run several kilometres down into the earth. The team has found that the water does not stay in these wells though, it seeps deeper into the ground and displaces naturally formed water pockets, causing massive pressure instabilities.
The effect is seen similarly in pools, the deeper you dive into the water the more pressure you feel on your head from the weight of the water above you. Since the wastewater is denser than regular water, there is a larger pressure increase at the bottom of the accumulated waste. As the pressure builds, faults in the rock become destabilized, allowing for injection-induced earthquakes.
“The fluid pressure from the injection destabilizes faults and causes earthquakes”, Ryan explains.
The team plans to take their findings and turn the data into a highly accurate model that could potentially simulate the associated hazard of one of these earthquakes. These models are paramount for infrastructure on the surface, especially in highly populated cities.
As Ryan explains, “That information can be passed over to the civil engineers and the city planners and the people that make decisions about how to handle infrastructure.”
The ultimate goal is to assist affected cities and towns in remaining safe despite the increase in earthquake magnitude. Whether from wastewater or from a tectonic plate, earthquakes are destructive and the more prepared we are for them the better it is for everyone.
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