GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 3.2 701 subsidence (Teatini et al. , 2011; Carminati et al. , 2006) and influenced by climatic changes (Simeoni and Corbau, 2009). The multi-methodological analysis consisted of histogram analysis of cumulative and mean annual values, centered moving average, cross wavelet transform and wavelet transform coherence analyses (Grinsted et al. , 2004), which have deepened the understanding of the relationship between ground surface and water system (rain-, river- and ground-water) and unveiling the important role of the hydrological load in driving the seasonal effects. Then, as it concerns the second step of the proposed procedure, a physically-based modelling of the hydrological surface loading (http://loading.u-strasbg.fr/displacements.php) has been chosen that relies on the Modern-Era Retrospective analysis for Research andApplications (MERRA2) (Gelaro et al. , 2017) and Global Land DataAssimilation System (GLDAS) (Rodell et al. , 2004). Once the seasonal oscillations have been modelled, the geodetic velocity has been calculated within a time period of interseismic deformation (2012-2016), considering both original data and data residuated by the simulated periodic components. Data analysis. All data used in this work are available on open source websites and refer to 11 stations of the Po Delta area (see Fig. 1): ground level (CODI), Po River hydrometric level (Ariano SIAP), piezometric levels (Ariano del Polesine 134, FE35, FE31 and FE23 and Cà Verzola) and rainfall data (Copparo, Volano, Goro and Pradon Porto Tolle). CODI station is located at Codigoro, near Po di Volano River, and belongs to the GPS network of Nevada Geodetic Laboratory (MAGNET). CODI is placed on the roof of a one-floor building whose foundations do not exceed 2 m of depth and lay on 15 m of deltaic and littoral sediments of the last prograding sequences. The daily series clearly exhibit non-tidal loading effects (i.e. atmospheric pressure, ocean bottom pressure and hydrological loading). Meanwhile, the 6-months moving average points out the presence of a clear annual signal with variable amplitude, the 12-months centered moving average applied on the whole data set reveals a gentle lowering trend plus a quite regular narrow oscillation characterised by an inter- annual period (~ 2 years). The wavelet analysis confirms the presence of these two stronger power peaks at about 1-year and 2.1-years period both in the geodetic time series and also in the hydrometric level of Po di Goro River. Moreover, at these scales, the two analysed signals share a common spectral power with a phase difference of about 180°, suggesting that a loading Fig. 1 - Po Delta area and data sites: continuous GPS (red square), pluviometric (blue circles), piezometric (black points) and hydrometric stations (green triangle).