GNGTS 2019 - Atti del 38° Convegno Nazionale

68 GNGTS 2019 S essione 1.1 this underground groundwater monitoring the data has revealed the existence of an aquifer behaviour characterized by very high dynamics. The data collected during these 4 years turned out to be quite a useful tool to a) characterize the background in the groundwater monitoring, and b) identify more clearly the observed anomalies and the possible link with deformation phenomena of tectonic interest. In this respect, the anomalies observed in the hydraulic pressure before the 24 August 2016, Amatrice earthquake are definitely impressive (De Luca et al. , 2018). Fig. 1 shows unprocessed data (at a 20 Hz sampling rate) of the hydraulic pressure from 19August to 5 September 2016 with a 60 s moving average (blue line). The presence of average information emphasizes the structural change of the signal (asymmetry). The novelty coming from our time series of hydraulic pressure concerns the presence of unambiguous signals starting about 5 days before the main shock of 24 August (De Luca et al. , 2018). To investigate in a quantitative fashion these rather unexpected phenomena we performed an elementary statistical analysis of the pressure time series looking at the first moments of full time-series. More specifically, after subtracting the (60 s) moving average we evaluated the variance (m2), the skewness m3/(m2)3/2 and the kurtosis (m4/m22 – 3) of the resulting distribution, see Fig. 2 (De Luca et al. , 2018). Fig. 2 - Statistical analysis: Kurtosis (blue) and Skewness (red) values from 15 June 2016 (167 doy) to 4 September 2016 from hydraulic pressure data. The statistical indicators are evaluated each 60 s. The plotted values are one hour averages. Data missing (194-201 doy) is due to instrumentation maintenance. The Amatrice earthquake (M w 6.0): 24 August (doy 237), 01:36:32 UT. The evidence of a signal change is already very clear about five days before the main shock. We have checked the relevance of this signal looking at the kurtosis of the full dataset (1 May 2015 to 5 September 2016) and found no significant deviation from the zero value until 40 days before the main shock (De Luca et al. , 2018). Further investigations on the relationships between earthquakes and groundwater variations in the vicinity of a large seismogenic faults are needed for a full understanding of the distribution of pre-seismic, coseismic and post-seismic variations and of their driving mechanisms. References Barnhoorn A., Cox S. F., Robinson D. J. and Senden T. Stress- and fluid-driven failure during fracture array growth: Implications for coupled deformation and fluid flow in the crust. Geology 38, 779-782; doi: 10.1130/G31010.1 (2010). De Luca G. La Rete Sismica regionale d’Abruzzo e sua integrazione con la RSN. Da Miscellanea INGV, Riassunti estesi del I° Workshop Tecnico: Monitoraggio sismico del territorio nazionale: stato dell’arte e sviluppo delle reti di monitoraggio sismico – Roma 20-21 Dicembre 2010, pp. 22-23 (2011). De Luca G., Di Carlo G. and Tallini M. Hydraulic pressure variations of groundwater in the Gran Sasso underground laboratory during the Amatrice earthquake of August 24, 2016. Annals of Geophysics 59, Fast Track 5; doi: 10.4401/AG-7200 (2016).