## 4 Results
### Correlation of MS Events with Environmental Factors  
By observing the cumulative curves of MS and false events for the entire monitoring period, different trends in the occurrence of these two classes are evident (Figure 10). Although both curves show increasing rates during periods with similar climatic and weather conditions (P1, P2, P3), the occurrence rate of false events is significantly higher than the rate of MS events. Moreover, another peak in the event occurrence is found in the absence of rainfall and significant temperature fluctuations (P4). As already discussed, this effect can be interpreted as being derived from the influence of meteorological factors on the onset of frequent electrical disturbances. However, it must be noted that even MS events do not show negligible increasing rates during the same time intervals, except for P3. The analysis of the temporal evolution of the MS events highlighted the existence of several days in which more than five events occurred (Figure 10c). These peaks mostly clustered during the period between February and April 2018, when 63% of all events were detected. The highest peak in the daily distribution of MS events (32), which is also preceded and followed by days of intense MS activity, is located within a time window characterized by a sharp decrease in rock mass temperatures and consistent rainfalls/snowfalls. At the end of February 2018, the entire region of Central Italy experienced an extreme meteorological event due to an incoming perturbation associated with the burn, a cold north-easterly wind that is typical of the steppes of the Siberian region [17]. At the Acuto field laboratory, air and rock mass temperatures reached their minimum values of \(-\)7.7 \({}^{\circ}\)C and \(-\)3.8 \({}^{\circ}\)C, respectively, and almost 106 mm of rainfall occurred within a 7-day time interval. The sharp temperature decrease caused freezing conditions that remained stable for four days (from 25 February 2018 to 1 March 2018). This winter storm was responsible for a short and intense thermal transient in the seasonal temperature trend, representing an unprecedented event in the seven-year environmental monitoring dataset collected at the Acuto field laboratory (2015-2022). Apart from this short-term variation in the environmental boundary conditions that caused a significant acceleration in the occurrence of MS events, with 83 MS events concentrated in 12 days, other isolated MS peaks can be observed in Figure 10, especially during April 2018 (8 MS events on 24 April 2018), May 2018 (12 MS events on 27 May 2018), and June 2019 (16 MS events on 19 June 2019 and 7 MS events on 22 June 2019). However, their correlation with external continuous (i.e., thermal variations) and transient (i.e., rainfalls) stresses is not as straightforward as for the period in which the rock mass experienced freezing conditions. Unfortunately, it must be stated that due to the limited number of MS events collected during the discontinuous 20-month MS monitoring, a statistical analysis aimed at deepening the correlations between rainfall, temperature fluctuations, and the occurrence of MS events, as suggested by [PERSON] [43] and [PERSON] et al. [8], was not performed. To achieve preliminary insights into potential cause-and-effect relationships between the abovementioned factors, the analysis of the temporal evolution and distribution of MS events was approached by employing an observational-based approach. An attempt to investigate the influence of temperature fluctuations on the local MS activity was made by analyzing the distribution of MS events during the heating and cooling phases of the rock mass (Figure 11). To this aim, the heating and cooling ramps of rock temperature timeseries were analyzed, and the minimum and maximum recorded values were extracted along with their average duration for each day of the monitoring period. Therefore, MS events were classified according to the ramp in which they occurred to highlight any recurrent pattern in their distribution on the daily timescale.