Displacement field of the Italian area from permanent GPS stations

A network of nine permanent GPS stations, six of them located in Italy (Cagliari, Matera, Medicina, Noto, Padova and Torino), the other three in Central Europe (Graz, Zimmervald and Wettzell) was been analyzed four times from October 1996 till 1998. After the GPS data processing, a rigorous statistical analysis based on the F (Fisher) test applied on the detected coordinate differences showed significant displacement at Matera, Medicina and Noto. The mean velocities computed for these sites with respect to Wettzell are (0.6 ± 0.3) cm/yr for Matera, (0.7 ± 0.2) cm/yr for Medicina and (0.6 ± 0.3) cm/yr for Noto. GPS velocities agree with those derived by VLBI and ITRF96 solutions, provided error ellipses are taken into account. The deformation analysis of the last time span shows a suspicious horizontal jump at Padova of (1.0 ± 0.1) cm corresponding to an antenna changing within the same period. This fact shows, in spite of the care used in permanent GPS installation, how the results of the deformation analysis may be strongly conditioned by site problems.