Topo-Iberia GPS network: Preliminary results at UJA analysis centre

The project “Geociencias en Iberia: Estudios integrados de topografia y evolucion 4D: Topo-Iberia” (Ref.CSD2006-00041) is supported by the Spanish Ministry of Science and Innovation. Its objective is to understand the interactions in the Iberian Peninsula (SW Europe) between deep, shallow and atmospheric processes, through a multidisciplinary approach linking Geology, Geophysics and Geodesy. As part of this project a network of 26 continuous GPS stations, covering the Spanish part of the Iberian Peninsula (22 stations) and Morocco (4 stations) has been established. The major objective behind the establishment of this array is to monitor millimetre level deformation of the crust due to African and Eurasian tectonic plates. More specific goals of the project include the identification of the areas and/or specific seismic faults which exhibit higher deformation rates, which could imply an increased seismic hazard in these specific areas. In December 2008, the network installation was completed and all the stations were fully operational. Data analysis is performed at three different analysis centres: Real Instituto y Observatorio de la Armada (ROA), University of Barcelona (UB) and University of Jaen (UJA). Different approaches to processing GPS data by using different software are being carried out. Preliminary coordinate time series and a first analysis of these results at UJA analysis centre are presented. Topo-Iberia Continuous GPS Network An array of new continuous GPS stations has been installed complementing other GPS networks already deployed by different Institutions (EUREF, IGS and Regional Government Agencies). After an initial period of design, purchase of new equipments, monumentation and deploying stations, nowadays Topo-Iberia GPS network includes twenty-six operational stations (Figure 1). Autonomous systems were designed including a GPS receiver and choke-ring antenna, solar panel, two batteries and GPRS modem (Figure 2). The deployment of the network equipment started in early 2008 and all stations were operational by December 2008. 22 sites are in different regions of Spain and 4 sites are located in strategically chosen places in northern Morocco to complete the overview of the present-day kinematics in the Iberian Peninsula and southern neighboring areas including the Atlas chain. Figure 1. Map of Topo-Iberia CGPS Sites Data Processing at University of Jaen Data Analysis of the whole set of new and existing CGPS stations is performed at three different analysis centres: “Real Instituto y Observatorio de la Armada” (ROA), University of Barcelona (UB) and University of Jaen (UJA) by using different software: GIPSY-OASIS, GAMIT and Bernese, respectively. The data analysis at UJA is performed by the Bernese Processing Engine (BPE) of the software Bernese 5.0 (Dach et al., 2007), using the phase double differences as observables. The IGS precise orbits and Earth’s orientation parameters are kept fixed and the absolute elevation-dependent phase centre corrections, provided by IGS (Dow et al, 2005) are applied. We have estimated each daily solution in a loosely constrained reference frame, close to the rank deficiency condition. Each loosely constrained solution is realized in an intrinsic reference frame, defined by the observations itself, differing from day to day only for rigid network translations, keeping the site inter-distances always well determined. The constraints for the realization of the chosen reference frame are imposed only a posteriori. The daily loosely constrained cluster solutions are then merged into global daily loosely constrained solutions of the whole network applying a classical least squares approach (Bianco et al., 2003). Then this daily loosely solution is constrained to ITRF2005. We have estimated the velocity field by using a purpose-built software (NEVE) that manages the complete stochastic model. The velocity field is estimated from the ITRF2005 time series. We simultaneously estimate site velocities together with annual signals and sporadic offsets at epochs of instrumental changes. The errors associated to the velocities derive from the direct propagation of the daily covariance matrices. Preliminar temporal series have been computed with available GPS data since May 2008 (Figure 3). Figure 2. TGIL site (left), Solar panel (centre) and GPS receiver (right) GPS Velocity Field Velocities in ITRF2005 and residual velocities with respect to Eurasian fixed plate are shown in Figure 4. The Eurasia pole used is from Devoti et al. (2008) Figure 3. Time Series in N, E, UP comp. in ITRF2005 for TGIL (left) and FUEN (right) Figure 4. TopoIberia velocities in ITRF2005 (left) and with respect to Eurasian fixed plate (right)