GNGTS 2013 - Atti del 32° Convegno Nazionale

Slow transient recorded by the cGPS FreDNet network at the Adria northern tip (NE Italy) G. Rossi, D. Zuliani, P. Fabris OGS (Istituto nazionale di Oceanografia e di Geofisica Sperimentale), Trieste, Italy Introduction. In the last years the attention to GPS measurements increased enormously, for the capability of reconstructing plate boundaries and their movements, as well as faults activity at a more local scale. This implied also a continuous effort in increasing the reliability and accuracy of the measurements and of the calculus of the relative linear trends. Nowadays, having at disposal time series long enough (more than ten years) it is possible to begin to distinguish other terms that are superimposed to the linear trend, and hence to the rigid plate motion. In fact, Dong et al. (2002) and Blewitt and Lavallee (2002) identified annual and seasonal effects, while Smalley et al. (2005), Calais et al. (2005) evidenced some characters of the North-American plate movements that differ from the simple linear motion, and the interpretation of which is vividly debated. Also in our regions, Devoti et al. (2008; 2011) evidenced slow varying patterns in Italy at long-scale length (> 100 km) that cannot be explained by simple block models, and Nocquet (2012) interprets the observed velocity field in the whole Mediterranean region as a combination of localized and distributed deformation. These considerations are at the basis of the research here presented. Having a disposal a data set of continuous GPS measurements, of decadal average length, in an area of intense and complex tectonic phenomena, we tried to inquire whether deviations from the linear trend are present, and the possible physical origin. The data. The northern tip of the Adria microplate (NE-Italy) is continuously monitored by the Friuli Regional Deformation Network (FReDNet) of OGS (Istituto Nazionale di Oceanografia e Geofisica Sperimentale), consisting of 15 GPS/GNNS stations, the first 8 of which were installed between 2002 and 2004. The 10 stations of the Marussi network of the Friuli-Venezia Giulia regional council, some of which record continuously since 1999, provide additional information on the strain field in the region. Fig. 1 – Vectors of the yearly horizontal velocities for the sites of the two networks (yellow, FReDNet stations, green, Marussi network stations), calculated from the linear trend. Dashed: the vectors calculated on the shortest time series. 198 GNGTS 2013 S essione 1.2