Hydrogeological monitoring of groundwater resources within the High Valley of the Tenna River (Sibillini Mts. Range) and possible near-field effects from the 2016-2017 Central Italy seismic sequence

The high valley of the Tenna River is in the central-eastern part of the Sibillini Mts., Central Italy. Within a research agreement between the Sibillini Mts. National Park and the Geological Survey of Italy of ISPRA, hydrogeological surveys aimed to characterize the study area and evaluate possible near-field effects of the 2016-2017 Central Italy seismic sequence on the local groundwater resources, started in June 2018 and were performed until July 2020. Stream discharge and hydrochemical in situ measurements were carried out. The hydrogeological conceptual model built through a rectified cross-section along the high valley of the Tenna River suggested that the Capotenna sector acts as a groundwater recharge area. In this area, a possible post-seismic groundwater depletion, although not adequately quantified because of the limited availability of continuous pre-seismic monitoring data, may have enhanced the depletion already induced by the recent snow-rainfall “decrease”. During the monitoring period, the Scaglia Aquifer at Capotenna had seldom sufficient hydraulic potential to allow the drainage through the underlying marly low-permeability threshold. Along the Tenna streambed, at 1175-990 m a.s.l., groundwater inputs from the Basal Calcareous Aquifer and Maiolica Aquifer were evidenced, the latter by overflow on a low-permeability formation. At lower elevation (985-845 m a.s.l.), in a sector featured by the Basal Calcareous Aquifer, a complex situation of hydraulic exchange between groundwater and surface water was found, likely due to tectonic fragmentation of hosting rocks and/or to the quite thin aquifer sustained by low-permeability layers (evaporitic and marly deposits). The main contributions of this paper, with respect to previous studies on the hydrogeological effects of the 2016-2017 seismic sequence in the Sibillini Mts., were the reconstruction of a local conceptual model, the analysis of groundwater-surface water exchanges along the Tenna River, and the identification of elevation sectors with different hydraulic behavior.