Earthquake-related fluids behaviour at Salse di Nirano mud volcano field (Italy)

Salse di Nirano (Fiorano Modenese, Italy) host one of the largest mud volcano fields of Europe. They are positioned upon an anticline structure of the NE-verging fold-and-thrust Northern Apennine belt and emit fluids mainly consisting of clay mud, saline water and hydrocarbons (liquid and gas). Like most of the world’s mud volcanoes, their gas emissions are primarily composed of methane (> 98%), with minor contributions from carbon dioxide, nitrogen, and other hydrocarbons (Mazzini and Etiope, 2017). Two main fault and fracture systems (one NW-SE oriented and the other SW-NE/ENE-WSW oriented) allow fluids migration to the surface (e.g., Bonini, 2008). From a geomorphological point of view, Salse di Nirano are placed within a caldera-like depression presumably formed by progressive collapse due to degassing (e.g. Bonini, 2008) or as the final stage of mud diapir evolution (Castaldini et al., 2005).

As many world’s mud volcanoes, Salse di Nirano activity is closely linked to tectonic processes (Martinelli and Ferrari, 1991; Bonini, 2009). With the aim of studying the interplay between geofluids and seismicity, a multiparametric monitoring system was set up in 2023. Two distinct mud pools were selected for the continuous monitoring of mud level/density, temperature and electrical conductivity. In addition, a permanent station measuring CO₂ flux diffused by the soil was installed at the edge of the mud volcanoes field, where higher gas fluxes were detected (Ferrari et al., 2024). Recently, the station has been upgraded with a methane sensor. A meteorological station and a velocimeter were installed to monitor the atmospheric parameters and the seismic activity of the area, respectively.

Overall, the multiparametric monitoring system continuously recorded about two years of data. Periodic oscillations were identified, with some anomalous variations of mud level, temperature, electrical conductivity and soil gas flux that have been compared with environmental data (meteorological and soil-related) and seismicity. Notably, synchronous changes in mud pools electrical conductivity and soil CO₂ fluxes were detected in relation to two distinct seismic swarms occurred in February and August 2024. In addition, differences in the behaviour of the two mud pools were also observed throughout all the time-series and presumably point to extremely local conditions influencing the common feeding system. All these observations highlight the efficiency of the presented continuous multiparametric monitoring system in inferring new insights on mud volcano crustal fluids dynamics. This work reports the results achieved in the framework of the INGV-MUR project Pianeta Dinamico.

References

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Bonini, M.; 2009: Tectonophysics Vol. 474, pp. 723-735. doi:10.1016/j.tecto.2009.05.018.

Castaldini, D., Valdati, J., Ilies, D.C., Chiriac, C., Bertogna, I.; 2005: Italian Journal of Quaternary Sciences Vol. 18, n. 1, pp. 245-255.

Martinelli, G., Ferrari, G.; 1991: Tectonophysics Vol. 193, n. 4, pp. 397-410, https://doi.org/10.1016/0040-1951(91)90348-V.

Mazzini, A., Etiope, G.; 2017: Earth-Science Reviews Vol. 168, pp. 81-112, http://dx.doi.org/10.1016/j.earscirev.2017.03.001.

Ferrari, E., Massa, M., Lovati, S., Di Michele, F., Rizzo, A.L.; 2024: Frontiers in Earth Science Vol. 12, n. 1412900, pp. 1-26, https://doi.org/10.3389/feart.2024.1412900.