THE ASSOGEO GPS NETWORK TO MONITOR SURFACE VARIATION IN THE EMILIA ROMAGNA REGION (NORTH-CENTRAL ITALY): DATA MANAGEMENT, PRODUCTS AND PRELIMINARY RESULTS

Abstract

The global positioning system (GPS), in both static and kinematic modes, allows a highly accurate measurement of point coordinates and therefore is widely used for monitoring both slow and fast surface deformations. The information provided by a GPS network can be used at the regional scale, to evaluate tectonic and seismogenic structure evolutions [Hunstad et al., 1999; Pietrantonio and Riguzzi, 2004], such as the estimation of deformation rates in the central Apennine chain [Pesci and Teza, 2007], or at larger scale, to monitor gravitational macroscopic effects due to, for example, rock-mass collapses, landslide activations or other instabilities [Mora et al., 2003; Tzenkov and Gospodinov, 2003; Squarzoni et al., 2005]. The accuracies of GPS measurements are generally a few millimeters for the horizontal coordinate components and sub-centimeters for the vertical ones. In fact, the elevation is highly influenced by atmospheric perturbations, involving zenith delays, which are difficult to be completely removed by means of data modeling. When referring to high accuracy, GPS surveying implies the precise measurements of the vectors between two or more receivers (baselines), the so-called relative positioning: data can be acquired on static and rapid-static conditions, which require GPS stations to be stationary. Several permanent GPS stations continuously operate on the Italian territory, belonging to different institutes like IGS (International GPS Service), EUREF (European Reference Frame), ASI (Agenzia Spaziale Italiana), INGV (Istituto Nazionale di Geofisica e Vulcanologia) and others [Serpelloni et al. 2006; Falco et al., 2007; Devoti et al., 2008]. Due to the high efficiency of this surveying methodology, in the last few years, the number of GPS permanent stations has rapidly increased and continues to expand; the Earth Science Department of Siena University, for example, installed 8 new stations in 2003 to study the tectonic processes in the Central-Northern Apennines [Cenni et al., 2004]. Also private GPS networks planned for commercial civil proposal exist; in particular the ASSOGEO s.r.l (Italian Trimble provider), established a dense GPS network for real time positioning by means of the VRS (Virtual Reference Station) concept [Hu et al., 2003] and work is still in progress to cover the whole Italian territory with a mean size of about 20-50 km