The analysis of ten years of sampling of CO2 dissolved in the groundwaters of the Apennines showed its maximum concentration during intense seismic activity
In the Apennine chain, the emission of CO2 of deep origin appears to be well correlated with the occurrence and evolution of the seismic sequences of the last decade. This is the result of the study ‘Correlation between tectonic CO2 Earth degassing and seismicity is revealed by a ten-year record in the Apennines, Italy‘ conducted by a team of researchers from the Istituto Nazionale di Geofisica e Vulcanologia (INGV, Italy) and the University of Perugia (UNIPG, Italy) just published in ‘Science Advances’.
“For the first time an analysis of geochemical and geophysical data collected from 2009 to 2018 was carried out”, explains Giovanni Chiodini, INGV researcher and coordinator of the study. “Results of this research have shown a correspondence between deep CO2 emissions and seismicity. In periods of intense seismic activity, peaks in the deep CO2 flux are observed, meanwhile they dampen when the seismic energy and the number of earthquakes decrease”.
The Earth releases CO2 of deep origin mainly from volcanoes, although these emissions also occur in seismic areas where there are no active volcanoes. In particular, this phenomenon is more intense in regions characterized by extensional tectonics, such as the area of the Apennines.
“Although the temporal relationships between the occurrence of a seismic event and the release of CO2 are not yet fully understood”, continues Chiodini, “In this study we hypothesize that the evolution of seismicity in the Apennines is modulated by the rise of CO2 accumulated in crustal reservoirs and produced by the partial melting of the plate subducting beneath the mountain chain”.
The continuous large-scale production of CO2 at depth favors the formation of overpressurized reservoirs. “Seismicity in mountain ranges”, add Francesca Di Luccio and Guido Ventura, INGV researchers and co-authors of the study, “could be related to the depressurization of these reservoirs and the consequent release of fluids which, in turn, activate the faults responsible for earthquakes”.
The study was conducted by sampling the high-flow rate springs (tens of thousands of liters per second) located in the vicinity of the epicentral areas of the earthquakes that occurred in central Italy between 2009 and 2018. “These samplings allowed us to characterize the origin of the CO2 dissolved in the water of the aquifers and to quantify the amount of the dissolved deep CO2“, explains Carlo Cardellini, researcher of the Department of Physics and Geology of the University of Perugia, co-author of the discovery.
“The close relationship between the CO2 release and the number and magnitude of the earthquakes, along with the results of previous seismological surveys, indicate that the earthquakes in the Apennines occurred in the last decade are associated with the rise of deeply derived CO2. It is worth mentioning that the amount of CO2 involved is of the same order as that emitted during volcanic eruptions (approximately 1.8 million tons in ten years)”, concludes Chiodini.
Therefore, the results of the study provide evidence on how the fluids derived from the decarbonation of a subducting plate play an important role in the genesis of earthquakes, opening new horizons in the assessment of CO2 emissions at global scale. Finally, this work demonstrates and supports how the modern study of earthquakes requires a multidisciplinary approach in which geochemical, geophysical and geodynamic data need to be integrated.