GNGTS 2013 - Atti del 32° Convegno Nazionale

The observed uplift in the Northern Apennines, with rates mostly lower than 2 mm/yr, is consistent with the results obtained by repeated leveling surveys carried out over 129 years by the Istituto Geografico Militare Italiano (IGMI). This last investigation, performed along several lines crossing the chain from the Tyrrhenian to the Adriatic coasts, indicates maximum uplift rates in the range of 1-3 mm/yr (under the assumption that most of the Tyrrhenian side of the Central-Northern Apennines is essentially stable). The uplift of the Northern Apennines is consistent with the effects expected from the longitudinal shortening of the belt suggested by Mantovani et al. (2009) and Cenni et al. (2012, 2013). The part of Central Apennines centered on the L’Aquila area and the corresponding Adriatic side is characterized by small negative rates. Significant subsidence, with velocities up to 5-10 mm/y, occurs in the eastern Po basin zone, while minor (or positive) vertical movements are recognized in the western Po Valley. This considerable difference between vertical movements in the two parts of the basin cannot be simply imputed to different anthropogenic effects or to ground settlement (Teatini et al. , 2011; Bonsignore, 2008). The same pattern was highlighted by the results of repeated levelling measurements from 1897 to 1957 (Arca and Beretta, 1985), a period that preceded the strong increase of economic activities in the second half of the XX century. They found a mean uplift velocity of about 2-3 mm/y in the central-western part of the Alpine chain, reducing rapidly moving toward the Po plain and in eastern direction; the study pointed out that the eastern Po Valley were affected by subsidence, with rates increasing from west (1-2 mm/y) to east (5-7 mm/y), whereas the western part (Lombard plain) mainly undergoes uplift, generally lower than 2 mm/y, except a narrow EW belt in the Monferrato zone, where uplift rates even reach 3.5 mm/y. The effects of a complex interaction of different tectonic structures of the area clearly influences the vertical movements, masking the anthropogenic subsidence. The comparison between the high density GPS network and the results obtained previously (up to 2006) with different techniques (Baldi et al. , 2009; Bonsignore 2007) indicates that the rates Fig. 3 – The vertical kinematic pattern obtained after the combination of our solution and Euref, Amon and Regal solutions. 165 GNGTS 2013 S essione 1.2