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She says this "swarm-like behaviour" means that when a more significant earthquake strikes, for example a magnitude four, the "seismicity is increased for one to two hours, and then the system relaxes again".

“If it had a return to a lot of seismicity, like we saw in 2004, with gas release and ground deformation, that would be the kind of scenario that might lead to evacuation.”

Wastewater injection has induced small to moderate-sized earthquakes around the world, however, making it important to study how CO2 injection produces seismicity and whether it might also induce larger earthquakes.

"CO2 injection at Decatur is a good example. The first period of injection, the one we analyzed in the paper, led to hundreds of microearthquakes. The second period of injection, which took place at a shallower depth and not as close to the faulted basement, resulted in virtually no seismicity," Juanes said.

Injection rates in CO2 projects have been "much, much lower" than wastewater injection rates in the 2000s and 2010s, said Juanes, which might explain why moderate-sized induced seismicity hasn't been seen at carbon sequestration projects.