Crustal movements in northeastern Italy derived from permanent GPS stations

The horizontal absolute motion vectors of northeastern Italy, obtained from the GPS data of the permanent stations of the Department of Physics of the University of Bologna, are quite similar to the NUVEL1A NNR plate motion model. However, the results indicate that these sites are moving faster than predicted by the model and with azimuths slightly more northward oriented. The directions of absolute motion in the no-net-rotation system confirm the motion of the Adriatic plate in the global circuit where both Africa, Europe and the intervening Adriatic plate are moving north-eastward, although at different velocities and with small variable azimuths which determine relative plate interactions. The motions of the Marina di Ravenna, Medicina and Bologna stations are respectively 30.9, 27.6, and 29.4 mm/yr; Trieste moves at a rate of 27.9 mm/yr. The azimuths have similar values. The data suggest shortening of about 2-to-4 mm/yr between Trieste, located at the leading edge of the Dinarides orogen and the Emilia-Romagna Marina di Ravenna, Medicina and Bologna sites positioned above the Apennines accretionary prism. This can be interpreted either as active thrusting of the Dinarides or/and active thrusting in the Apennines accretionary prism. Seismic reflection profiles and seismicity indicate that both orogens are active, but the Dinarides appear to have slower convergence rates. Active thrusting supports the notion of a lively and retreating subduction beneath the northern Apennines. The height time data of the same sites show subsidence rates of different magnitude: Medicina -2.44 0.05 mm/yr; Marina di Ravenna –10.82 0.04; Bologna –17.93 0.09; Trieste –5.71 0.10. The rates of Marina di Ravenna and Bologna are, to a large extent, of anthropogenic nature. They were induced by groundwater exploitation, which was subjected to control policies only starting from the early 80's. These values indicate faster subsidence close to the depocenter of the Apennines foredeep (Bologna), with lower values above anticlines of the accretionary prism (Medicina). Subsidence in Marina di Ravenna can be interpreted as related to both foredeep subsidence plus sediment loading and natural and anthropogenic compaction in the Po delta area