GNGTS 2015 - Atti del 34° Convegno Nazionale

GNGTS 2015 S essione 1.2 89 Data base of Italian velocities and strain rates at permanent GNSS sites A. Caporali, M. Bertocco, J. Zurutuza University of Padova, Italy Introduction. The knowledge of the present day deformation rates at the Earth’s surface represents an important boundary condition for modeling deformation processes at depth, especially in areas such as Italy where the typical hypocentral depth is of the order of few tens of km. To reliably map the surface deformation on a regional scale the systematic timewise comparison of the coordinates of reference sites has proved to be a successful approach (see e.g. Caporali, 2003; Cenni et al. , 2012; Nocquet, 2012; Serpelloni et al. , 2005). In Italy there are over 400 permanent GNSS (Global Navigation Satellyte System) sites belonging to various Organizations which make the data freely available. In this paper we present the results of the analysis of such a network of 415 GNSS sites, with more to come as the time series become sufficiently long for a reliable estimate of the velocity. The University of Padova contributes to the GNSS activities: as Local Analysis Center of EUREF EPN is actively contributing to the maintenance of the European Reference Frame using state of the art software and analysis methods. The same analysis procedure and standards are used for processing on a weekly basis a network of over 450 permanent sites, which extends to cover surrounding countries. Consequently, updated time series of coordinates are regularly published on a dedicated web site (retegnssveneto.cisas.unipd.it) , under the auspices of the Regional Government of Veneto. This body of information forms the basis not only for updated coordinates of sites used in Real Time Kinematic surveying applications, but also for geodetic studies which can have a direct relation to seismicity and ground deformation. The aim of this paper is to review how this information is generated, and how it can be packed into a convenient format (e.g. .kml or .shp) for layering with other databases, such as the DISS 3.1.1 of INGV. Our data base includes all the information which can be useful e.g. for seismic hazard or dynamic modeling, such as velocities in a rigorously defined reference frame, strain rates and derived values such as the regional stress drop. The information on statistical seismicity referred to the Seismic Zones ZS9 of Meletti et al. ������ ����� ���� ��� �������� (2008) comes from the Catalogo Parametrico dei Terremoti Italiani CPTI04 (Gruppo di Lavoro CPTI04, 2004) updated with the more recentevents. ��� ���� ��� ������� ����� ��� ������ ���������� The data and kml/shp files are freely available. From raw GNSS data to mean velocities. We focus on accepted standards for data processing, which are based on the IGS (International GNSS Service http://igscb.jpl.nasa . gov) and EPN (European Permanent Network of EUREF http://epncb.oma.be and http://www. euref.eu ) to ensure implementation of state of the art reference frame, orbits, satellite clocks, antenna models, tropospheric modeling, elevation cutoff, and all those aspects of the processing which may affect the final coordinates at each epoch, and which make the processing products (weekly minimally constrained SINEX files representing the network adjustment) eligible for combination and stacking with other products (e.g. the weekly SINEX files of the EPN) (Lidberg et al. , 2014). We use consistently the Bernese 5.2 software both for the daily/weekly processing and the multiyear analysis by normal equation stacking (Dach et al. , 2013). The systematic processing of the Italian network started in 1996 with a very limited number of sites and with software, models and analysis procedures which have evolved in time. Only with GPSweek 1632 (April 17, 2011) consistent orbits, satellite clock models and antenna models, labeled IGb08 (Rebischung, 2012), were introduced. Normal equations prior to GPSweek 1632 use different analysis standards, and were therefore excluded from this analysis to ensure maximum compliance with the EPN Guidelines (Bruyninx et al. , 2013).The velocities of the GNSS sites are defined in terms of mean slope of the time series of their coordinates. To this purpose the coordinates must be defined in a same reference frame across the time span of the coordinate time series. The state of the art reference frame is at this time the IGb08