Abstract
We performed continuous recordings (May 2015 – January 2017) of hydraulic pressure and electrical conductivity of groundwater in the 190 m-long horizontal S13 borehole drilled next to the deep underground laboratories of Gran Sasso (LNGS-INFN), located in the core of the Gran Sasso carbonate aquifer (central Italy) at a distance of about 39 km south-eastward from the 24 August 2016 Amatrice earthquake (6.0 Mw) epicenter. Using a 3-channel, 24-bit ADC we achieved a sampling rate of groundwater physical properties up to 50 Hz for each channel. We focused on the analysis of data recorded before, during and after the Amatrice earthquake, describing and discussing in detail the evidence for significant hydraulic pressure and electrical conductivity anomalies recorded before the main shock. We identified unambiguous signals in the hydraulic pressure data starting on 19 August, i.e. five days before the 24 August mainshock. A more careful analysis allowed us to detect the inception of a weak change up to 40 days before the Amatrice earthquake and a significant variation in the electrical conductivity data about 60 days before. The data revealed highly dynamic aquifer behaviour associated with the uprising of geogas probably related to the preparation stage of the Amatrice earthquake.
Highlights
Earthquake prediction is a widely recognized goal as well as a challenging scientific problem because of its complexity and its social impact
We decided to monitor some physical parameters of the deep groundwater of the large Gran Sasso carbonate aquifer (Abruzzi region, central Apennines, Fig. 1) through a horizontal borehole placed in the highway tunnel very close to the underground laboratories of Gran Sasso (LNGS-INFN)
The horizontal S13 borehole (Figs 2 and 3) was drilled around the end of the 1980s in a hall excavated in Meso-Cenozoic limestones and dolostones close to the underground laboratories of Gran Sasso (LNGS-INFN)
Summary
Received: 19 May 2017 Accepted: 12 October 2018 Published: xx xx xxxx earthquake, central Italy. Those concerning the fault frictional properties in the presence of fluid can provide unique insights into fluid-rock interactions[34] In this framework, we decided to monitor some physical parameters of the deep groundwater of the large Gran Sasso carbonate aquifer (Abruzzi region, central Apennines, Fig. 1) through a horizontal borehole (named S13) placed in the highway tunnel very close to the underground laboratories of Gran Sasso (LNGS-INFN). The Gran Sasso chain is placed in a seismically active area of central Apennines, as demonstrated by the 6 April 2009, Mw 6.3 L’Aquila earthquake[38,39] and by the recent 24 August 2016, Mw 6.0 Amatrice earthquake[40,41] (Fig. 1), and provides a unique opportunity to study an inner, unexploited portion of a very large carbonate aquifer (about 1,000 km[2]). The initial 175 m of S13 borehole are tubed with a well casing, while the last 10 m drain inside the upper Triassic dolomite[54,55]
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