GNGTS 2016 - Atti del 35° Convegno Nazionale

238 GNGTS 2016 S essione 1.2 regional nature of the multi-year discharge observed at the Caposele spring and indicate that negative precipitation trends and aquifer exhaustion are associated with reduced or negative dilatational strain (T1), whereas episodes of increasing rainfall (aquifer recharge) are associated with enhanced dilatation (T2) (Figs. 1 and 2). Vertical displacements appear to be preferentially correlated with GRACE TWS data (Fig. 3), showing subsidence in high water storage periods (autumn-winter), and uplift in summer. At the multi-year scale, subsequent years of low TWS (e.g., 2007-2008 and 2012-2013) are associated with a general motion of uplift involving the whole studied area. According to the previous observations we hypothesize that: i) two main processes are responsible for the observed deformations and that ii) different spatial and temporal patterns allow us to observe their separated effects in the horizontal and vertical components. The high correlation with GRACE TWS suggests that, similarly to other regions (e.g., Borsa et al., 2014), the vertical component reflects the regional elastic response to variations of TWS Fig. 3 – Comparison between GPS time series and hydrological records (i.e. rainfall, spring discharge, equivalent water height GRACE). GPS time series (grey dots) are the detrended horizontal component along direction N45E at selected sites in the karst area. Note that vertical axes for CDRU is inverted for clarity. Daily precipitation data at Gioi Cilento (red line) and Senerchia (orange line) rain-gauges are represented as detrended cumulative rainfall. The blue line shows daily discharge data of Caposele spring. Monthly data of equivalent water height from GRACE satellite represent an average over the area under examination (green line ±1-sigma uncertainty). The dark red circles are stacked vertical GPS displacements sampled at the same epochs of GRACE (notice the inverted vertical axis).