Carbon dioxide earth degassing, heat flux and earthquakes in central and southern Italy

In recent years, many studies have been devoted to quantifying and mapping terrestrial CO₂ degassing. Besides climate effects, another reason to study the natural degassing of endogenous CO₂ concerns its role in tectonics, and here I will focus primarily on this aspect, referring to the results obtained in central and southern Italy. In central and southern Italy, non-volcanic CO₂ of deep origin is released from numerous vents and diffuse emission zones, and from groundwater with high CO₂ content. Groundwater degassing was estimated coupling hydrogeochemical and hydrogeological data and using the mass balance of the carbon dissolved in the springs of high flow rate (hundreds to thousands kg/s). This approach allowed us both to quantify the emission (2.1 × 10¹¹ mol yr⁻¹) and to create a detailed map of the process. The map shows two large degassing structures: TRDS (Tuscan Roman degassing structure) and CDS (Campanian degassing structure). The same CO₂-rich groundwater are “slightly thermal” having a temperature of few degree C higher than that expected for normal groundwater. These anomalous temperatures are due to high geothermal heat fluxes (up to 350 mW/m²). This coincidence, combined with the presence at depths > 10 km of a large zone of low-velocity of the seismic waves, suggested that the hot CO₂-rich fluids are probably emitted from a large magmatic intrusion located in the root of the central Apennines. The Apennine belt is characterized by seismicity that recently peaked with strong earthquakes in 2009 (L'Aquila earthquake, M = 6.3) and 2016 (Amatrice-Norcia earthquakes, M = 6.0 and 6.5). We observed that CO₂ emissions correlate with seismicity both geographically and over time: Apennine seismicity affects in fact the eastern edges of the TRDS and the CDS, and CO₂ emissions increased during, and likely before, the 2009 and 2016 events.