During earthquakes, cobwebs of faults open beneath the earth, so that gases deep in our planet can seep upwards. The researchers have now compiled the first long-term record that shows a connection between earthquakes and the release of carbon dioxide gas.
While the amount of carbon dioxide released by tectonic activity compared to the billions of tons that are, a pittance is human activity pumps into the atmosphere each year. The study, published Wednesday in Science Advances, sheds light on the planet's climate-controlling carbon cycle.
"It modulates the earth's climate on geological timescales," said James Muirhead, a geologist at the University of Auckland in New Zealand, who was not involved in the research and praised the data set collected by a team of Italian scientists.
The results could possibly pave the way for the prediction of seismic activities.
The region around the central Apennines in Italy, about an hour east of Rome, is full of flaws. Devastating earthquakes have ravaged the area repeatedly, including the L & # 39; Aquila earthquake in 2009. That tremor that killed hundreds of people hit the headlines again in 2012 when a judge ruled seven Italian earthquake experts guilty of manslaughter were because they had not warned local residents of the potential risk nearby. The area's seismic activity has been linked to carbon dioxide leakage.
Giovanni Chiodini, geochemist at the National Institute for Geophysics and Volcanology in Bologna, and his colleagues analyzed the carbon content of the groundwater in the Apennines. From April 2009 to December 2018, the researchers collected hundreds of water samples from 36 different sources. They calculated the carbon dioxide concentration in each sample after subtracting the contributions from rainwater and soil.
The researchers estimated that about 1.7 million tons of carbon dioxide were released in the study area over a decade due to tectonic activity. This roughly corresponds to the carbon dioxide that is released during a volcanic eruption.
The real surprise came when Dr. Chiodini and his co-workers compared their data with records of approximately 17,000 nearby earthquakes. The researchers found that seismic activity and carbon dioxide gassing clearly tracked each other over time – periods of high seismic activity associated with spikes in gas release. For example, the carbon dioxide concentrations measured in the months after the L’Aquila earthquake were about twice as high as in 2013, a period of low earthquake activity, the team showed. In September and November 2016, high concentrations were measured again, just a few months after several large earthquakes hit the region.
Scientists believe that this relationship makes sense, based on the miles below the surface. The central Apennines are located on a subduction zone where carbon-rich rock slabs continuously plunge downwards. As these stones sink they are exposed to ever hotter conditions until they melt, releasing gases, said Dr. Chiodini. "There's a huge source of carbon dioxide a hundred kilometers below the Apennines," he said. When the pressure builds up underground, the crust will eventually break and cause earthquakes.
Earthquakes themselves could also trigger stronger carbon dioxide emissions, suggest the scientists. That's because ground movement can cause gas bubbles to form underground, much like shaking a bottle of champagne, said Dr. Chiodini. This feedback loop could help explain aftershocks in the Apennines, the researchers suggest.
The big question is what happens first, the earthquake or the carbon dioxide gas emission.
"If the carbon dioxide emissions are when the great earthquakes are advanced in time, these methods could possibly be used along with other instruments as earthquake indicators," said Dr. Muirhead.
But a lot more observations – with measurements closer in time – would be required, he said, and even then it would still be a difficult task to predict seismic activity. "The uncertainties are still too high and the consequences too great," he said.