Comparison between Periodic Tracer Tests and Time-Series Analysis to Assess Mid- and Long-Term Recharge Model Changes Due to Multiple Strong Seismic Events in Carbonate Aquifers

Abstract

Understanding the groundwater flow in carbonate aquifers represents a challenging aspect in hydrogeology, especially when they have been struck by strong seismic events. It has been proved that large earthquakes change springs hydrodynamic behaviour showing transitory or long-lasting variations and making their management much more difficult. This is the case of Sibillini Massif (central Italy), which has been hit by the well-known 2016–2017 seismic period. This work aims to improve the knowledge of carbonate aquifers groundwater circulation and their possible changes in the hydrodynamic behaviour, during and after a series of strong seismic events. The goal has been achieved by comparing long-time tracer tests and transient time-series analysis, based on a sliding-window approach. This approach allowed investigating transient variations in the carbonate aquifers recharge system, highlighting the changes of relationships between the inflow contributions to the spring discharge in the area. As a result, the seismically triggered pore pressure distribution, and the hydraulic conductivity variations, because of the ground shaking and the fault systems activation, account for all the mid- and long-term modifications in the recharge system of Sibillini aquifers, respectively. These outcomes provide valuable insights to the knowledge of aquifer response under similar hydrogeological conditions, that are vital for water management.

The Role of Faults in Groundwater Circulation before and after Seismic Events: Insights from Tracers, Water Isotopes and Geochemistry

“…In particular, the regional Basal aquifer complex (BAS) is hosted by the Upper Triassic-Lower Jurassic formation of Calcare Massiccio (600-700 m thick), a limestone deposed in a carbonate platform disarticulated in different domains, and by Corniola, a 150-400 m thick pelagic limestone formation. These formations overlie a Triassic dolomite and evaporite sequence acting as an aquiclude complex (TRI) and are characterized by a well-developed karstic system [11,37]. BAS recharges several punctual springs and it is responsible for the discharge increasing along the watercourses due to the intersection between the riverbed and the saturated portion of the aquifer, resulting the so called linear springs characterised by high discharge, widely occurring in the entire Mts.…”

“…Only a small number of these works actually deal with the changes in the role of a certain fault system before and after the seismic period [10]. However, the latter is really a crucial aspect in hydrogeological studies, especially when they concern groundwater management issues [11]. In fact, it is known that faults behave either as conduits or barriers with respect to groundwater flow depending on their kinematics and fault rock lithology [12,13], but the age-old problem of identifying if they limit or even block the flow of groundwater or if they rather act as a preferential flow path is partially still unsolved [14].…”

“…In Italy, some authors suggested different interpretations to explain groundwater modifications due to the main earthquakes occurred in the country [27][28][29][30]. As concerns the strongest earthquake occurred in Italy during the Amatrice-Norcia seismic sequence (August 2016-January 2017), some models were in fact proposed to justify the spring and river discharge change occurred in the area [11,31,32]. All the proposed models deal with observed springs and streams discharge variations before, during and after the seismic period [33][34][35][36].…”

“…All the proposed models deal with observed springs and streams discharge variations before, during and after the seismic period [33][34][35][36]. In the same area [37] and [11] showed some correlation between discharge data and rainfall-snowfall events, coupling the latter with long time artificial tracer tests. Although many efforts were then made to suggest a preliminary hydrogeological conceptual model of the area after the seismic sequence, a specific study aiming to investigate the transfer of groundwater through fault zones in the northern portion of the area, adding some specific data to subsurface geology reconstruction has never been conducted before.…”

Assessing Stream-Aquifer Connectivity in a Coastal California Watershed

“…Drawdown response in observation wells does not attain a steady state as predicted by the models, at least for the pumping duration typically used in such tests. Numerical modeling and long-term hydraulic process monitoring at the field scale as performed recently by [26,27] in Italy hold significant promise for quantifying and assessing stream-aquifer interactions.…”