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When an earthquake struck the Italian mountainous city of L’Aquila in April 2009, few people would have thought that carbon dioxide had anything to do with it. But geologists took up the case immediately.
In the immediate aftermath of the L’Aquila earthquake, a team from the Italian National Institute of Geophysics and Volcanology began measuring carbon dioxide bubbling in nearby springs, hoping to detect what terrestrial processes, in addition to plate tectonics, might have been involved. triggered the seismic shock. .
They continued to sample spring water through 2018, comparing pulses of dissolved CO2 gas that originated deep underground with records of seismic activity. In that time, two more major earthquakes would shake the region.
L’Aquila is located among the Apennine mountain range that runs along the Italian peninsula. Beneath L’Aquila, northeast of Rome, lie two underground aquifers that feed on surface springs. This is where the researchers were able to measure the CO2 coming out from below.
CO2 ejections in earthquake zones have been measured in the Apennines and elsewhere before, for example at points along the East African rift that runs through Ethiopia to Mozambique.
But this decade-long geochemical research reveals, for the first time, the relationship between earthquakes and buried CO2 that escapes along faults through springs and vents over time. It hints at how powerful CO2 could be below the ground and could bolster predictions for upcoming earthquakes.
The rise of buried CO2 begins when the tectonic plates below the Apennine mountain range grind up, heating and melting the carbonate rocks from which they are made, and releasing the CO2 stored within them.
The gas constantly accumulates in reservoirs about 10 to 15 kilometers (6 to 9 miles) underground and dissolves in groundwater basins it encounters on its way to the surface.
By measuring the carbon content in 36 springs around L’Aquila between 2009 and 2018, the researchers showed how this process aligns with seismic activity.
“The Apenninic earthquakes in the last decade are clearly associated with the deeply derived CO2 rise,” they said in a press release.
The amount of deep CO2 dissolved in the spring water increased and decreased in parallel with the number and intensity of earthquakes over time. Emissions peaked during large earthquakes and periods of intense seismic activity, then declined as the energy of an earthquake and its aftershocks waned.
Carbon dioxide reaches the surface in a spring near the epicenter of the 2009 L’Aquila earthquake. (Giovanni Chiodini, INGV)
We still can’t say if the CO2 surge caused any earthquakes or if the emissions were just a burp-like side effect. However, the researchers believe that CO2 is continually rising from great depths, weakening crust fractures as pressure increases.
They also have a hunch that the first tremors of an earthquake could cause a sudden release of more gas bubbles from deep CO2 deposits, much like the burst of bubbles you’d see after shaking a soda bottle, and trigger more. replicas.
“Analysis of groundwater makes it possible to investigate relatively large areas and related tectonic processes on a regional scale,” the authors said.
From their measurements, the researchers could, for now, estimate the total amount of CO2 expelled in a decade by tectonic activity in this part of the Apennines.
Their answer: 1.8 million tons of carbon, which is roughly the same amount of CO2 that explodes in the atmosphere when a volcano erupts. It is also comparable to the carbon emitted by 350,000 cars driven in one year.
What this study shows is that considerable amounts of CO2 are purged from faults in the earth’s crust, mostly without detection (although these emissions are nowhere near the billions of tons emitted by human activities). Still, with the future climate of our planet at stake, this source is something that we must factor into our carbon budgets.
“Studying groundwater in tectonically active areas would be a powerful tool to better estimate the global budget for tectonic carbon dioxide emissions to the atmosphere,” the researchers said.
They plan to install a monitoring system in the Apennines to help conduct further analysis and to test whether rising CO2 could warn of seismic activity. The more measurements the better.
“We hope that continuous monitoring of water springs is the best way to track deeply produced CO2 emissions to better understand the causal relationship with seismicity,” the team said.
The study was published in Scientific advances.
