GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.1 67 BEFORE, DURING AND AFTER THE AMATRICE EARTHQUAKE (24 AUGUST 2016): A RECORD OF CHANGES IN THE GRAN SASSO GROUNDWATER G. De Luca 1 , G. Di Carlo 2 , M. Tallini 3 1 Istituto Nazionale di Geofisica e Vulcanologia – Osservatorio Nazionale Terremoti, L’Aquila 2 Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali del Gran Sasso, L’Aquila 3 Università degli Studi dell’Aquila – Dipartimento di Ingegneria Civile, Edile-Architettura e Ambientale, L’Aquila Chemical and physical groundwater parameters are monitored in seismogenic areas worldwide, principally by measuring and analysing water level and hydrochemistry changes in wells, springs and streams to find possible correlations with local and regional seismicity and between their spatial and temporal variations and strain processes (Manga and Wang, 2015 and references therein). Moreover, in the past few decades many studies have suggested a connection between fault mechanics and underground fluid dynamics, and a large quantity of experimental results and models have appeared in the literature (Barnhoorn et al. , 2010; Di Toro et al. , 2011; Violay et al. , 2013; Hirth and Beeler, 2015; Sibson, 2000; Scuderia et al. , 2017). In this framework, starting from May 2015, we have performed continuous recording of the hydraulic pressure, of deep groundwater in the 190 m-long horizontal S13 borehole drilled next to the underground INFN laboratories ( LNGS ), located in the core of the Gran Sasso carbonate aquifer below a 1,400 m-thickness of rock. The aquifer is located in a seismically active area, as demonstrated by the 6April 2009, Mw 6.3 L’Aquila earthquake and by the recent 24 August 2016, Mw 6.0 Amatrice earthquake. The distance of Amatrice earthquake location from our S13 borehole is about 39 km. A seismographic station of the national seismic network of Istituto Nazionale di Geofisica e Vulcanologia (INGV) is located about 250 m from the S13 borehole inside the national underground laboratory of Gran Sasso (LNGS-INFN). The station (international code: GIGS) was deployed in the framework of the GINGER experiment and is equipped with a Nanometrics Trillium 240 s (see http://cnt.rm.ingv.it/en/instruments/station/GIGS for further details). The area is also monitored by a dense regional seismic network (De Luca, 2011). Our experimental equipment includes a 3-channels 24-bit ADC (mod. SL06 by Sara Electronic Instruments – http://www.sara.pg.it/ ) set up in continuous local recording. We started data acquisition on 1 May 2015 by continuous high-frequency sampling (10-50 Hz) of hydraulic pressure (De Luca et al. , 2016; De Luca et al. , 2018). This experimental system is still in acquisition. During these last 4 years of continuous recording (May 2015 – September 2019) the hydraulic pressure signal showed the annual cycle of charge and discharge of the aquifer and follows the sun/moon tides, as expected (De Luca et al. , 2018). Furthermorer during Fig. 1 - Plot of the hydraulic pressure (in MPa) at 20 Hz sampling rate (15 August, 228 doy to 4 September, 248 doy, 2016). The blue line represents the 60 s moving average. The box shows the enlargement of the signal corresponding to the Amatrice earthquake, 24 August, 01:36:32 UT, 237 doy, (Mw 6.0); the red line represents the vertical component of broadband seismic station ( GIGS ) equipped with a Trillium 240 s seismometer; the black line is the hydraulic pressure expressed in MPa. The time scale starts from 01:36:30 (UT) of 24 August 2016.