Observing the earth at regional and local scale by means of space geodetic techniques

Vertical land movements over northern Italy are presented. In this domain, the Po plain is of a particular interest because it is subjected to both natural and anthropic subsidence. Vertical rates derived from two ensembles of leveling measurements performed by IGM during the periods 1877–1903 and 1950–1956 were compared with those obtained from the analysis of the GPS data collected during the last two decades. The GPS network consists of about 130 stations distributed over an area spanning 7° in longitude, from 7° to 14°, and 3° in latitude from 44° to 47°. The vertical deformation relevant to the two investigated periods, and obtained by means of the two different techniques, shows comparable main features: uplift up to a few mm/year in the western sector and subsidence in the central-eastern part. Across the Po plain, subsidence ranges from a few to several mm/year, particularly in urban areas, in the Po river delta and south of it along the Adriatic coast. However, the recent estimates provided by the GPS data indicate a general reduction of subsidence rates with respect to the leveling results. A reduction up to 3 mm/year is found in the Po river delta and along the Adriatic coast. Accurate knowledge of vertical land motion is desirable when studying sea-level variations by means of tide gauge data. We discuss the time series of two tide gauges located in the northern Adriatic, namely, Venice and Marina di Ravenna, and compare the sea level rates obtained from these data corrected for vertical land motions with those deduced from satellite altimetry measurements.