GNGTS 2017 - 36° Convegno Nazionale

204 GNGTS 2017 S essione 1.3 from Europe and Japan MSAS and has 440 channels available to receive satellite signals. The receiver allows nominal accuracies of ± 5 mm in the horizontal and ± 7 mm in the vertical. The antennas installed are Trimble Zephyr Geodetic II, “Ground Plane” type, which are designed to reduce the effect of Multipath and offers sub-millimeter precision in the centering phase. Daily GPS solutions are processed with GAMIT/GLOBK version 10.61 (Herring et al. , 2015). GAMIT/GLOBK is a comprehensive suite of programs for analyzing GPS developed at MIT, the Harvard-Smithsonian Center for Astrophysics (CfA), and the Scripps Institution of Oceanography (SIO) for estimating GPS station coordinates and velocities, stochastic or functional representations of post-seismic deformation, atmospheric delays, satellite orbits, and Earth orientation parameters. GAMIT is collection of programs to process phase data to estimate three-dimensional relative positions of ground stations and satellite orbits, atmospheric zenith delays, and earth orientation parameters. The software is designed to run under any UNIX/ LINUX operating system. GLOBK is a Kalman filter whose primary purpose is to combine geodetic solutions (GPS, VLBI, SLR) of different epochs in a unique solution. The input data are the covariance matrices for station coordinates, earth-orientation parameters, orbital parameters and relative positions constrain in a reference frame (coordinates and velocities of reference frame); the results are the estimation of precise coordinates and velocities. We use several GPS stations from the International GNSS Service (IGS) located in the stable South American plate and 18 stations of the Geodetic Colombian Network GEORED (Geodesia: Red de Estudios de Deformación - https://geored.sgc.gov.co/) to define regional (South America) and local (North Andes block) reference frame. Results and modelling. The 2010-2015 GPS time series show a constant inflation trend and the tilt data shows different inflation periods (Fig. 2). To interpret the cause of ground deformation and understand the source characteristics we inverted the GPS displacements using dMODELS. dMODELS is a MATLAB software package for modeling crustal deformation near active volcanoes that model physical characteristics of a source (location, depth, radius, pressure and volume change) and compute the best-fit between observed and modeled data (Battaglia et al. , 2013). The best-fit for the GPS data of NRV between 2012 and 2015 is represented by a spherical source (McTigue, 1987) located 8 km SW from the main crater (Fig. 3). This source ascended between June 2012 and December 2015 from a depth of 17 to 7 km, Fig. 3 - Deformation velocities vectors at Nevado del Ruiz. Red arrows represent the observed data and blue arrows the best-fit model. The yellow circle represents the positioning of the best fit source.