# Multidisciplinary Study of Mud Emissions Following the 2016 Norcia Earthquake
## 4 Results  
### Mud Chemistry  
The electrical conductivity (EC) of the analyzed muds ranges from 1.61 to 3.52 mS/cm, corresponding to non-saline (0 < 2 ms/cm) and very slightly saline (2 < 4 mS/cm) muds (U.S. Salinity Laboratory Staff [54]). The highest EC value was measured in the ML3-A sample, whereas ML1-A had the lowest salt content.  
The measured pH\({}_{\mathrm{Ca}}\) values are from 7.8 to 8.3, revealing neutral to weakly alkaline muds. In alkaline soils, pH is generally controlled by carbonate, often related to sodium. In the analyzed muds, the major ions are Na\({}^{+}\) and alkalinity, showing a correlation trend despite a Na/alkalinity ratio of >1. Only sample ML1-A has a stoichiometric Na-HCO\({}_{3}\) composition.  
The sulfates show high variability, from 5.81 to 13.42 meq/L. The highest SO\({}_{4}\)\({}^{2-}\) concentration belongs to sample ML3-A, which also has the highest EC. The analyzed mud samples are depleted in Ca\({}^{2+}\) and Mg\({}^{+2}\), maybe due to phosphate precipitation processes typical of alkaline sediments. The nitrate concentrations are generally low, excluding anthropogenic pollution, except for samples 3 and SV1-A, which have relatively high NO\({}_{3}\)\({}^{-}\) values, around 0.8 meq/L.  
The fluorine content of the muds is relatively high, ranging from 0.061 meq/L (sample 1) to 0.326 meq/L (sample ML3-A). The natural fluorine concentration is generally high in mud, since it is directly related to the clay content [55]. However, contamination with fluorine-bearing phosphorous fertilizers could also enhance this element's presence in soils.  
The chlorides are generally low (from 0.21 to 1.57 meq/L), and bromides are below the detection limit in all the samples. The low salinity and low Cl\({}^{-}\) and Br\({}^{-}\) concentrations hint at a continental origin of the muds.  
The high Na\({}^{+}\) values and the depletion of Ca\({}^{2+}\) and Mg\({}^{2+}\) suggest cationic exchange processes mainly involving Na\({}^{+}\)-bearing minerals and Ca-rich waters. Another Na\({}^{+}\) source could be due to the alkali feldspars weathering, recognized in SEM-EDS analyses.  
The wide range of SO\({}_{4}\)\({}^{2-}\) concentrations may be due to one or more sources for this ionic species, such as: (1) the leaching and dissolution of Messinian gypsum evaporitic horizons, present in the Colombacci and Laga formations (e.g., [38]) and (2) the contribution of fertilizer-polluted waters associated with moderate-to-high levels of nitrate, as occurring for sample 3.  
According to the literature, shale formations are suitable for mud volcano formation, favored by a combination of gravitative instability of shales and fluid overpressures, e.g., Kopf [16] and Mazzini and Etiope [15]. Fluid overpressures can develop in the shale formation or in surrounding sedimentary rocks.  
The low salinity of the analyzed muds suggests a continental origin, consistent with the Colombacci Formation rather than the Argille Azzurre Formation. The Colombacci Formation includes evaporite horizons, mainly gypsum, which could explain the high SO\({}_{4}\)\({}^{2-}\) concentrations in water extracted from the muds. The semi-quantitative SEM-EDSanalyses of the muds are compatible with the Colombacci origin since they recorded the presence of quartz, Fe-rich mica, alkali feldspars, carbonates, and clay minerals.  
The geochemical analyses of mud volcanoes extruded from the Argille Azzurre formation at Salse di Nirano (Modena province, Italy) show higher EC values, ranging from 2.72 to 26.60 mS/cm and a Na-Cl composition typical of marine sediments [23].