GNGTS 2014 - Atti del 33° Convegno Nazionale

(1) where A 1k and v 1k are, respectively, the intercept and trend of the best fitting straight line, the g 1kj terms are the N instrumental or seismic steps eventually occurred at the Tj epochs, H is the Heaviside step function. These parameters are estimatedwith aweighted least squaremethod, using as weight the uncertainties associated to the components estimated in the GAMIT processing. 3) Spectral analysis: the residual time series obtained by modelling the linear motion by mean of the parameter estimated in the previous step [Eq. (1)], are analyzed with a nonlinear least squares technique to estimate spectra (Lomb, 1976; Scargle, 1982). The spectrum of each component is analyzed in order to estimate the period P of the principal signal, in the interval between seven days to half of the observation time span. 4) Parameter estimate: the daily position component y 2k (t) (k=1,2,3, for the north, east and vertical component respectively) has been modelled by only considering the principal periodic signal resulting from the spectral analysis phase. The daily time pattern of each component y 2k (t) can be re-written as: (2) where A 2k and v 2k are the re-estimated intercept and constant velocity, the B k and ~ are respectively the amplitude and phase of the principal periodic signal P. The g 2kj terms are the re-estimated offset magnitudes for the N identified discontinuities due to instrumental changes or seismic events eventually occurred at the T j epochs, H is the Heaviside step function. The velocity uncertainties are estimated adopting the Allan Variance of the Rate (AVR, Hackl et al., 2011), in order to taking into account the time correlated noise σ k (t i ) in the time series Thepresent-dayvertical kinematic pattern in the Italian peninsula is shown in Fig. 2. This pattern presents some significant features, in particular the sites located in the Alps and Apennines are characterized by uplift, with a low rate, while the sites located in the Po Plain and in some basins of the central and northern Apennines are characterized by subsidence. �� ��� ����� ��� ������ In the Alps, the uplift rates are of the order of a few mm/yr, in agreement with previous estimates carried out by repeated leveling in the last century. At present, the uplift of that zone is attributed to the combined effects of tectonic Fig. 1 – Vertical velocities and contour map obtained considering the stations with an observation time span longer than 2.5 years. The interpolation pattern has been estimated using the kriging geostatistical method over a regular spaced grid (0.2°x0.2°). 136 GNGTS 2014 S essione 1.2