Aug. 26 (UPI) -- Geologists have discovered a link between carbon dioxide degassing patterns and earthquake incidence in Italy's Apennine Mountains, according to a study published Wednesday in the journal Science Advances.
Over millions of years, carbon dioxide in the atmosphere gets trapped in rocks and minerals called carbonates through a variety of chemical and biological processes. When tectonic forces heat and melt deep-lying rocks, CO2 gets released and slowly rises toward the surface.
According to the new study, the process is closely linked with seismicity.
Researchers first discovered a spatial correlation between Earth's seismic zones and evidence of deep CO2 emissions during the 1970s. In 2004, the authors of the latest paper were able to show that deep CO2 degassing and seismic activity are correlated across Italy.
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"Now, with this work, we observe that peaks in the deep CO2 flux occur concurrently with the most energetic earthquakes while the gas flux decreases when the seismic energy and the number of earthquakes decrease," lead author Giovanni Chiodini, told UPI in an email.
"This correlation for a relatively long period is a new result suggesting a causal relation between earthquakes and Earth degassing," said Chiodini, a researcher at Italy's National Institute of Geophysics and Volcanology.
Between 2009 and 2018, researchers in Italy regularly measured the amount of carbon dioxide in freshwater springs fed by two major aquifers near the epicenter of the L'Aquila earthquake that devastated several cities and towns in central Italy's Abruzzo region in 2009.
Because different carbon sources yield different ratios of carbon isotopes, researchers were able to isolate carbon released by deep-lying rocks from carbon released from other sources.
By measuring the isotopic composition of dissolved carbon in the water samples, researchers were able to identify changes in the amounts of CO2 released via tectonic degassing over time.
"We determined for each sample the concentration of the carbon derived from the deep source," Chiodini said. "With this approach we exclude from the computation the CO2 derived by other processes such as the shallow dissolution of calcite and the fraction of CO2 dissolved by the water during the infiltration in the soils containing organic matter."
The data showed increases in CO2 emissions from deep sources was closely correlated with increases in local seismic activity. Researchers aren't certain yet whether CO2 degassing directly causes earthquakes, or whether tectonic movements simply allow more CO2 to reach the surface, they said.
There's probably a little bit of both happening, but researchers said the data and the findings of other studies suggest there is causation.
"It is not possible to unequivocally answer in a definitive way at that time," Chiodini said. "We think, however, that the continuous production at depth of large amounts of gas -- mostly derived from decarbonation of subducting rocks rich in carbonates -- can have an active role in seismogenesis and, more in general, in the tectonics of the region."
Researchers said they hope that by continuing to monitor CO2 degassing in places featuring significant tectonic activity, they'll be able to isolate predictive patterns that might help scientists more accurately estimate the risk of an earthquake in specific locations.
In the meantime, researchers suggest their findings can be used to improve carbon cycling models.
"This work and other previous works show how large amounts of deep CO2 can be dissolved in groundwaters," Chiodini said. "This significant fraction of Earth degassing is, generally, not considered in the global budget of the CO2 naturally emitted by the Earth and it is, at the present, underestimated."
