Mefite d’Ansanto CO2 emission area (Southern Apennines, Italy): first results on the uppermost crustal structure from teleseismic data.

The Mefite d’Ansanto is the largest non-volcanic low temperature CO₂ natural emission on the Earth (Di Luccio et al., 2023). It is located in the Southern Apennines, about 25 km away from the northern tip of the seismogenic structures of the November 23, 1980 M_S = 6.9 earthquake. The main gas emissions manifest in a roughly circular depression with about 100 m of diameter, whose centre is characterized by bubbling mud. The emissions of CO₂, likely of mantle origin, are probably fed by the reservoir found at Mt. Forcuso 1 well (Chiodini et al., 2010), located approximately 2 km east of Mefite area. In the framework of the Strategic INGV FURTHER Project, on 29 September 2020 a local seismic network was installed to investigate on the possible links between the fluid movements at depth and the seismicity of the area surrounding the CO₂ emission site (Cusano et al., 2021; Morabito et al., 2023). With the aim of obtaining information on how large the emission area is and on its sub-surficial structure, we investigated the crustal structure beneath Mefite d’Ansanto and the surrounding area analysing the waveforms of teleseismic events. We selected deep and intermediate earthquakes that have impulsive onset, epicentral distance ∆ ≤ 90° and magnitude M ≥ 6.0. The seismic traces are those recorded by MEFA, a temporary seismic station installed at Mefite d’Ansanto, and by CAFE, SNAL and RFS3, permanent seismic stations belonging to the INGV National Seismic Networks. We, first, utilized cross-correlation technique to check the similarities among the waveforms (Milano et al., 2023). Successively, we computed synthetic seismograms to obtain the best fit with the recorded seismograms. The synthetic seismograms were computed by means of QSEIS6 software (Wang, 1999), fixing a starting velocity model extracted from that IASPEI91 (www.iris.edu). Successively, we perturbed it beneath the study area taking also into account the upper crustal structure recently retrieved for the Irpinia region (e.g., Feriozzi et al., 2024). The cross-correlation analysis had already revealed some particularities in the waveforms suggesting similarities in the uppermost crust beneath MEFA and RSF3 stations, approximatively 2.5 Km apart. The first results from the synthetic seismograms evidence that the phase with the on-set in the range 4.5-5 s from the first arrival at each stations, is compatible with the P-to-S converted phase at Moho discontinuity.

Chiodini et al., 2010, Geophys. Res. Lett., 37, L11303.

Cusano et al., 2021, https://doi.org/10.5194/egusphere-egu21-10625.

Di Luccio et al., 2022, https://doi.org/10.1016/j.earscirev.2022.104236.

Feriozzi et al., 2024, https://doi.org/10.1029/2023TC008056.

Milano et al., 2023, https://doi.org/10.4430/bgo00416.

Morabito et al., 2023, https://doi.org/10.3390/s23031630.

Wang, 1999, Bulletin of the Seismological Society of America, 89(3), 733-741.