A study from the University of California, Riverside, has determined that fracking — the process of injecting liquid at high pressure to force open fissures and extract oil or gas — causes slow, small tremors or earthquakes.

The researchers looked specifically at fracking done using liquid carbon dioxide instead of the commonly used wastewater — a process that pushes carbon underground, preventing it from trapping heat in the Earth’s atmosphere.

Source: Fracking Lawyer/CC BY 3.0

Despite making this process more environmentally friendly than using wastewater, which doesn’t keep carbon out of the atmosphere, the researchers determined that both approaches lead to these small tremors.

To make this determination, the researchers installed seismometers — instruments for detecting and measuring earthquakes via converting vibrations due to seismic waves into electrical signals — all along a Kansas fracking site. For six months, data were examined during the complete fracking injection period in addition to the month before the injections and the month following injections.

The team discarded background noise from the seismometers to demonstrate that the remaining signals were produced underground and only occurred when fluid injections did. Because the researchers didn’t detect the tremors before or after the injections, the team concluded that the tremors were associated with them.