GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 1.2 235 and long-term deformations of tectonic nature (e.g., interseismic strain, postseismic and volcanic deformation) (e.g., Blewitt and Lavalée, 2002); iii) thanks to their high accuracy, geographic distribution and temporal continuity, continuous measurements from GPS networks provides an unique contribution to the study of hydrological processes in different aquifer systems and geological environments (e.g., Borsa et al. , 2014). In this work we describe for the first time an hydrologically-related, multi-year transient signal in time series of continuous GPS stations in south-central Italy related to the deformation of karst aquifers. A dense continuous GPS network with more than 10 years of data at several stations, and the presence of large calcareous ridges able to store a huge quantity of water (Fiorillo et al. , 2015) provide the opportunity to study the role of time-dependent climatic variability and aquifer recharge conditions in driving deformation of karst aquifers. The transient signal highlighted in this study (Fig. 1) reveals a significantly high amplitude (up to 1 cm) in the horizontal components of GPS sites distributed over a large area (length scales of tens of kilometers). This signal interferes with and modulates the ≈3 mm/yr steady-state extensional opening in the axial part of the Apennines (D’Agostino, 2014). We analyze horizontal and vertical GPS time series integrated with rainfall data, karst spring discharge time series and estimates of terrestrial water storage (TWS) from the GRACE (Gravity Recovery and Climate Experiment) satellite. We highlight a clear association of the observed horizontal transient deformation to phases of recharge and discharge of the karst aquifers, whereas the vertical Fig. 1 – Observed (colored dots) time series at some sites in Southern Italy (Fig. 2). Black dashed line represent a 6- months Gaussian filter of the time series. GPS sites are ordered from the Tyrrhenian coast (bottom) toward the Adriatic coast (top). Left: horizontal component projected along a direction perpendicular to the long-axis of the Apennines (N45E); center: horizontal component projected along a direction parallel to the long-axis of the Apennines (N135E); right: vertical component. Uncertainties have not been plotted for clarity. T1 and T2 refer to the two time intervals in which velocities represented in Fig. 2 are calculated.