No abstract

Study of the tectonically active L'Aquila

A seismic sequence in central Italy from August 2016 to January 2017 affected groundwater dynamics in fractured carbonate aquifers. Changes in spring discharge, water-table position, and streamflow were recorded for several months following nine Mw 5.0-6.5 seismic events. Data from 22 measurement sites, located within 100 km of the epicentral zones, were analyzed. The intensity of the induced changes were correlated with seismic magnitude and distance to epicenters. The additional post-seismic discharge from rivers and springs was found to be higher than 9 m 3 /s, totaling more than 0.1 km 3 of groundwater release over 6 months. This huge and unexpected contribution increased streamflow in narrow mountainous valleys to previously unmeasured peak values. Analogously to the L'Aquila 2009 postearthquake phenomenon, these hydrogeological changes might reflect an increase of bulk hydraulic conductivity at the aquifer scale, which would increase hydraulic heads in the discharge zones and lower them in some recharge areas. The observed changes may also be partly due to other mechanisms, such as shaking and/or squeezing effects related to intense subsidence in the core of the affected area, where effects had maximum extent, or breaching of hydraulic barriers.

The Mw = 6.3 L'Aquila earthquake on 6 April 2009 produced a mainshock that caused significant changes in the hydrogeology of the Gran Sasso carbonate fractured aquifer: (i) the sudden disappearance at the time of the mainshock of some springs located exactly along the surface trace of the Paganica normal fault (PF); (ii) an immediate increase in the discharge of the Gran Sasso highway tunnel drainages and of other springs and (iii) a progressive increase of the water table elevation at the boundary of the Gran Sasso aquifer during the following months. Using the data collected since the 1990s that include aftershock monitoring as well as data regarding spring discharge, water table elevations, turbidity and rainfall events, a conceptual model of the earthquake's consequences on the Gran Sasso aquifer is proposed herein. In this model that excludes the contribution of seasonal recharge, the short-term hydrologic effects registered immediately after the mainshock are determined to have been caused by a pore pressure increase related to aquifer deformation. Mid-term effects observed in the months following the mainshock suggest that there was a change in groundwater hydrodynamics. Supplementary groundwater that flows towards aquifer boundaries and springs in discharge areas reflects a possible increase in hydraulic conductivity in the recharge area, nearby the earthquake fault zone. This increase can be attributed to fracture clearing and/or dilatancy. Simulations by numerical modelling, related to pore pressure and permeability changes with time, show results in accordance with observed field data, supporting the conceptual model and confirming the processes that influenced the answer of the Gran Sasso aquifer to the L'Aquila earthquake. Copyright (C) 2010 John Wiley & Sons, Ltd

Karst springs in central-southern Italy are largely exploited for the human consumption since the Roman Times and currently feed some tens of millions inhabitants with tap water of high quality. Unlike other karst springs, they are characterized by a steady rate during the year with modest seasonal variability. However, the effects of climate changes are being strongly perceived in central and southern Italy as in the rest of the Mediterranean basin, and groundwater is obviously also affected. In this paper, we analyze the discharge time series of some important karst springs in the region, evaluating the trends and fluctuations in relation to rainfall regime, on a yearly time scale. The aim is to evaluate the response of these large karst aquifers in the Mediterranean area to the recharge input variation. The role of the North Atlantic Oscillation has also been considered. Trends and fluctuations have been highlighted by n-years moving average and transforming the time series by the Rescaled Adjusted Partial Sum. The results show that a drop in the discharge has occurred since 1987, with reductions ranging from 15 up to 30 %, although this negative trend is now possibly attenuating or even reversing. As a final remark, the spring discharge of the large karst aquifers in central-southern Italy can be assumed as a robust indicator for climate changes as it integrates the effects of precipitation and temperature variation in time and space. © 2014, Springer-Verlag Berlin Heidelberg