Research ArticleGEOCHEMISTRY

Correlation between tectonic CO2 Earth degassing and seismicity is revealed by a 10-year record in the Apennines, Italy

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Science Advances  26 Aug 2020:
Vol. 6, no. 35, eabc2938
DOI: 10.1126/sciadv.abc2938
  • Fig. 1 Map of the seismicity and of CO2 Earth degassing and location of investigated aquifers.

    (A) Map of the M > 2 1986 to 2020 Italian seismicity recorded by the INGV (Istituto Nazionale di Geofisica e Vulcanologia) seismic network (terremoti.ingv.it; last accessed January 2020). (B) Studied aquifers and springs and the post-2007 seismicity. The main flow lines of the groundwaters are reported as arrows. Map of the CO2 flux, modified from (17, 29), is shown in the background of both (A) and (B). Coordinates are reported in UTM-WGS84-32N.

  • Fig. 2 Temporal evolution of CO2 degassing and seismicity.

    (A to C) Chronograms of the earthquake magnitudes compared with the concentration of deeply derived carbon (Cdeep) in the monitored springs. (D) Binary plots of Cdeep of the monitored springs against the log number of the earthquakes occurred at distances <45 km in a period of 80 days centered at any sampling date. (E) Chronogram of the earthquake magnitudes compared with the daily amount of deeply derived CO2 dissolved by the groundwaters of the Velino aquifer (FCO2).

  • Fig. 3 CO2 sources and dissolved carbon in the monitored springs.

    δ13Cext versus Cext diagram of the monitored springs from the Velino aquifer. Measurements are compared with the theoretical compositions obtained adding a deep inorganic CO213C = −1.48‰) to normal groundwaters. Samples taken in periods close to the main earthquakes (red symbols) show evident shifts toward the same deep CO2 component (i.e., of similar isotopic carbon signature) that enter the aquifer during the quiescence periods (white symbols).

  • Fig. 4 VP anomalies and source of the CO2.

    The image highlights a negative anomaly in the seismic velocity variations (DVp %) at 16-km depth [P-wave model (38)]. We interpret this anomaly as a deep gas storage zone that provides deeply derived CO2 to the above located Velino aquifer. The top of the low VP zone is located at a depth of 10 to 15 km [see Fig. 7 in (39)]. Coordinates are reported in UTM-WGS84-32N.

  • Fig. 5 Carbon dissolved in Velino and Gran Sasso groundwaters.

    (A) TDIC versus δ13CTDIC diagrams of the sampled water. Group A groundwaters (normal groundwaters) follow a trend expected for an infiltrating water dissolving an isotopically “light” biogenic CO2. Group B and C groundwaters follow a trend compatible with the input of inorganic CO2, characterized by a heavier δ13C value. The high TDIC and the δ13C values of group C suggest that these groundwaters are affected by CO2 degassing before the sampling. (B) 1/Cext versus δ13Ccext diagram. The diagram allows the estimation of the isotopic composition of the deeply derived CO2 and the infiltrating water end members.

Supplementary Materials

  • Supplementary Materials

    Correlation between tectonic CO2 Earth degassing and seismicity is revealed by a 10-year record in the Apennines, Italy

    G. Chiodini, C. Cardellini, F. Di Luccio, J. Selva, F. Frondini, S. Caliro, A. Rosiello, G. Beddini, G. Ventura

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