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A plan to inject millions of tonnes of carbon dioxide into the seafloor off Canada鈥檚 west coast appears to come with very little risk of triggering an earthquake. But such 鈥渋nduced seismicity鈥� could be an issue for carbon storage projects elsewhere.

Carbon capture and storage involves capturing carbon dioxide from the air or from a source of emissions and permanently storing it 鈥� usually underground 鈥� in order to reduce the amount of the greenhouse gas in the atmosphere. To date, almost all captured and stored CO2 has been injected into oil and gas reservoirs, usually as a way of extracting more oil and gas. Other storage projects 鈥� such as one operating in Iceland 鈥� inject CO2 into basalt rock, where it gradually forms into solid calcium carbonate.

Basalt suitable for this kind of permanent CO2 storage is hard to come by on land, but the rock is abundant beneath the seafloor, says at the University of Victoria in Canada. She and her colleagues found the has large amounts of suitable basalt. The group has applied for permission from the Canadian government to inject a small amount of CO2 at a site around 200 kilometres off the coast as part of a feasibility study.

Eventually, the researchers hope to inject millions of tonnes of CO2 at the site each year, either captured from onshore sources and then carried via pipeline or ship to the injection site, or captured directly from the atmosphere on an offshore platform above the site. 鈥淚f you utilise the whole basin, [it could store] 750 gigatonnes [of CO2],鈥� says Moran.

However, the Cascadia basin is seismically active, and the researchers wanted to address concerns that pumping large amounts of CO2 into the seafloor might increase the pressure within nearby faults in the bedrock and trigger earthquakes. The worry is that such quakes could 鈥� or that they could release CO2 from the site. 鈥淲e decided to be proactive,鈥� says Moran.

Moran and her colleagues used data from boreholes drilled near the proposed injection site and other seismic data to model 131 nearby faults. They estimated how much pressure has naturally built up at each fault and how much more would be needed to cause each one to slip. They then modelled how injecting different amounts of CO2 would affect the pressure within the faults.

They found injecting 2.5 million tonnes of CO2 each year at the site over 10 years would have virtually no risk of triggering an earthquake on any of the faults. 鈥淭he risk is minimal,鈥� says Moran. 鈥淚t鈥檚 slim to none in this location.鈥�

鈥淚t鈥檚 a pretty innocuous place,鈥� says at Oregon State University, who is not involved with the project. He says earthquakes have happened near the proposed injection site, but none large enough to cause damage on land. The real risk of a 鈥淏ig One鈥� in the Cascadia basin comes from the very large Cascadia fault, which lies more than 100 kilometres to the east of the proposed injection site, much too far to be affected by the project. 鈥淚t really has absolutely nothing to do with it,鈥� says Goldfinger.

However, at the University of Bristol in the UK says the researchers don鈥檛 have sufficient data about the site鈥檚 geology for him to be confident in their assessment of the risk of triggering nearby earthquakes. 鈥淭he history of induced seismicity is littered with case examples of over-confident fault stability assessments that have been proved wrong,鈥� he says.

Moran agrees that uncertainties are involved, but points out the site is too far from the coast for it to pose a risk to people, even if there was a quake there. She adds that any would form into solid hydrates on the seafloor due to the water pressure and never make it to the atmosphere. 鈥淚t is a very safe location,鈥� she says.

At other proposed CO2 storage sites nearer to people, however, triggering earthquakes , especially as carbon storage projects scale up, says at the Swiss Federal Institute of Technology in Zurich. Although CO2 has unique properties, he says the problem could come to resemble induced seismicity related to expanding fracking for oil and gas. 鈥淐O2 injection is probably going to be a significant part of hitting climate change targets, so this is a problem we鈥檒l have to manage, if and when it happens,鈥� he says.