Carbon dioxide from Earth’s mantle may trigger some Italian earthquakes

Italy may owe some of its seismic activity to carbon dioxide bubbling up from deep underground.

The country’s central Apennine Mountains region has been rattled by several destructive earthquakes in recent years, including the devastating magnitude 6.3 quake that wracked the city of L’Aquila in 2009 (SN: 8/14/09). A new decade-long record of natural carbon dioxide emissions in the area reveals that spikes in CO₂ release coincided with the biggest earthquakes. That finding hints that CO₂ rising toward Earth’s surface can change pressure along faults to trigger earthquakes, researchers report online August 26 in Science Advances. Understanding the relationship between CO₂ and seismicity could someday lead to better earthquake forecasts.

Earth naturally releases carbon dioxide when tectonic forces melt carbonate rock in the mantle, a process that frees CO₂ (SN: 10/1/19). That CO₂ rises, gathers in pressurized pockets in Earth’s crust and seeps into groundwater that feeds springs aboveground. Previous studies have noted that CO₂ tends to escape Earth in seismic hot spots. But without long-term records of CO₂ emissions in earthquake-prone areas, no one knew exactly how the timing of carbon emissions compared with earthquake occurrence. 

From 2009 to 2018, researchers measured the carbon content of springwater fed by the Velino aquifer, which is near the epicenter of the 2009 L’Aquila quake and sits atop a reservoir of CO₂ in Earth’s crust. Those data show that jumps in CO₂ emissions happened at about the same time as strong earthquakes, and emissions dropped off when quakes were smaller and farther between. When the region was struck by quakes of magnitude 6 or higher, the Velino aquifer springs released more than 600 metric tons of CO₂ per day. During more seismically quiet periods, the springs emitted some 400 to 500 tons of CO₂ daily.

Still, these data do not conclusively show whether rising CO₂ helps incite earthquakes, or if the shaking ground simply brings more CO₂ to the surface, says Andrea Billi, a geologist at the Italian National Research Council in Rome not involved in the work. “It’s a chicken-and-egg problem.” Continuously monitoring these types of carbon dioxide emissions in the Apennines and other seismically active regions, such as California and Japan, could reveal whether uprising gas is a precursor or product of quakes, he says.

“I think there is feedback between the two,” says study coauthor Giovanni Chiodini, a geologist at the Italian National Institute of Geophysics and Volcanology in Bologna. Continuous buildup of carbon dioxide underground, he says, could drive earthquakes, which fracture Earth’s crust and allow more CO₂ to creep upward, which in turn generates more quakes.

If uprising CO₂ does aggravate seismic activity in some areas, then tracking the chemistry of local springwater may offer forecasters a new tool to make their predictions, which scientists did not have when the deadly earthquake took L’Aquila by surprise in 2009, Billi says. In the wake of that disaster, six Italian scientists and a government official were convicted of manslaughter for failing to adequately warn the public of seismic risks in the region — although the defendants were later acquitted or got reduced sentences (SN: 1/23/13).