## 4 Results
### Correlation of MS Events with Environmental Factors
This evidence is also strengthened by the almost-perfect correlation between the 1 h rate of event occurrence and the evolution of daily temperature ranges and 1 h temperature rates, with the absolute highest MS peak (32 events) occurring immediately after a day characterized by a 14.5 \({}^{\circ}\)C daily thermal excursion and a maximum temperature rate of 4 \({}^{\circ}\)C/h (Figure 12b). Furthermore, the occurrence of MS events during the winter storm appears to be clustered during the heating phases of the rock mass. It must be considered that the scarce correlation between MS events and rainfalls during this time interval may be in part biased by the fact that the rain gauge mostly measured snow melt. In fact, the weather station was not equipped with a invometer and, since the quarry was completely covered by snow during these days, the analysis of the correlation between MS events and rainfalls could not be thoroughly investigated. Nevertheless, after the end of the buran storm, a significant increase in rainfall was observed between 5 March and 8 March, but no MS events were recorded, except for an isolated peak that was triggered and characterized by a delay of two days. This evidence highlights that the microseismicity observed during the freezing period is more likely related to the rapid decrease and increase in near-surface temperatures. Thermally induced stresses are in fact able to drive differential strain variations, especially in the outermost layers of rock masses, where their amplitude is highest, resulting in contraction and expansion cycles of fractures and microfractures that can eventually lead to their genesis or propagation [19; 44; 62]. In addition, if considering the amount of rainfall that occurred before the winter storm, a freezing and thawing mechanism may also be invoked to justify the numerous MS events detected during this short time interval. The persistent freezing conditions might have favored the formation of ice inside fractures and microcracks during the cooling phases of the rock mass, leading to the accumulation of inelastic strain at the tip of discontinuities [63]. Then, the rise in temperatures during the first stages of the heating phases, driven by high positive thermal gradients, might have caused the rapid ice melting followed by a consequent stress release that could be considered the primary cause of the intense MS activity. This evidence is limited to this time window which is characterized by extreme and non-representative conditions of the normal climatic setting of the Acuto quarry area. Figure 12: Comparison between environmental factors and the occurrence of MS events for the periods between February 2018 and March 2018 (**a–c**), and April 2018 (**d–f**) and June 2019 (**g–i**): 10 min air (blue line), rock mass temperature (red line), and 1 h cumulative rainfall (green line) (**a**,**d**,**g**); daily temperature range (i.e., thermal excursion) (black line) and 1 h rock temperature rate (blue line) (**b**,**e**,**h**); daily distribution of MS events occurred during the heating phase (red bars) and cooling phase (blue bars) of the rock mass along with the 1 h cumulative MS events curve (black line) (**c**,**f**,**i**). The other two investigated periods are instead more representative of the environmental boundary conditions of the area. For example, during the second period spanning from 8 April 2018 to 25 April 2018, 29 MS events were detected, but this value is certainly underestimated due to the periodic interruption of the MS monitoring system at night (Figure 12d-f). Near-surface temperatures show a decreasing trend during the first days (from 8 April to 13 April) that is related to a minor meteorological perturbation which caused temperature rates and gradients to significantly vary (Figure 12e). One of the most distinct features of this monitoring interval with respect to the winter storm is represented by the higher correlation that can be found between MS events and rainfalls, rather than with temperature fluctuations.