GNGTS 2014 - Atti del 33° Convegno Nazionale

be attributed to lateral lithospheric heterogeneities and/or to an incomplete removal �� of the OTL effect (Baker and Bos 2003). �� We have computed the corrected tidal residual vectors X (X, χ ) = B (B, β) - L (L, λ ) of the main tidal waves. For each wave, R (R, 0) represents the Earth model tidal vector, L (L, λ ) represents the indirect effect (OTL) computed for a given ocean tide model and B (B, β) = A c (A c ,α c ) – R (R, 0) represents the vector difference between observed and Earth model spectral component (Melchior and Francis, 1986). B depends on the contribution of the OTL (Jentzsch, 1997). The Xcos χ component of the corrected residual vector X, which is in phase with the body tide, would be sensitive to the anomalous regional Earth’s response to the tidal stress (�� lateral heterogeneity), although calibration errors could also affect this component (Baker and Bos, 2003). �� The Xsin χ component reflects instrumental noise and/or effects not considered in the model. �� It is significant when higher than 2 nm/s 2 (Melchior, 1995). Some parameters of the tidal residual vectors are given in Tab. 3. The tidal analysis of the gravity records over more than 3 years (May 2011 – July 2014) after all yielded amplitudes and phases of the main waves of the gravity tide in the Calabrian region. The whole of the obtained tidal spectral components represents, for the time being, the first synthetic model of the gravity tide in the region. The gravity contribution at the Cosenza station of the ocean tides has been removed from the recorded gravity changes to compute, via ETERNA, amplitudes, amplification factors δ and phase shifts of the main waves of the tidal field. �� The slope of the regression line correlating the values predicted by the DDW99/NH model and the values obtained through the computed tidal parameters, results 1.002 � �� ± 0.001, with a standard deviation σ = 14 nm/s 2 . The ratio �δ M2 /δ O1 results 1.007 ± 0.002 consistent with the value 1.006 expected by the �� DDW99/NH �� model. The predicted values by DDW99/NH model fairly fit the observed tidal field in the region. The tidal residual vectors have been also computed. �� The meaning of such residuals is debated. In the past, some authors (e.g. �� Melchior and Francis, 1986; Yanshin et al., 1986; Robinson, 1993�) suggested the existence of correlation between local deviations of some lithospheric parameter from the model assumed as reference (here the DDW99/NH) and the in phase component of the X corrected residuals (mainly of M 2 wave). Statistical analyses carried out by Shukowsky and Mantovani (1999) have shown a significant correlation between the tidal residuals of the M 2 wave and the effective elastic thickness of the lithosphere. Objections to these hypotheses originate from the results obtained by other researchers (e.g. Rydelek et al. ,1991; Fernandez et al. , 2008) leading to the conclusion that the corrected residual vectors X chiefly depends on the instrumental noise and the inadequacy of the adopted OTL models. �� We focus here our attention on the main lunar tidal waves M 2 and O 1 (Tab. 3). �� The residual Xcosχ component of the M 2 wave turns out negligible while, on the contrary, the Xsinχ is not negligible. This result would exclude any correlation with lateral heterogeneity of the lithosphere beneath the Calabrian region and is probably imputable to inadequacy of the OTL model. The opposite can be observed in the O 1 residual which has a significant Xcosχ component and a negligible Xsinχ Tab. 3 - Residual vectors for the main tidal waves at Cosenza. Wave B ( nm/s 2 ) X ( nm/s 2 ) Xcos χ ( nm/s 2 ) Xsin χ ( nm/s 2 ) M 2 18.8 ± 0.3 10.1 ± 0.3 0.5 ± 0.01 10.1 ± 0.3 S 2 7.6 ± 0.4 4.4 ± 0.4 -1.5 ± 0.2 4.1 ± 0.3 K 1 7.4 ± 0.6 6.7 ± 0.6 4.7 ± 0.3 4.7 ± 0.5 O 1 5.7 ± 0.6 6.8 ± 0.6 6.8 ± 0.6 -0.5 ± 0.02 N 2 3.7 ± 0.4 2.0 ± 0.4 1.0 ± 0.2 1.8 ± 0.3 K 2 1.8 ± 0.4 1.0 ± 0.4 0.20 ± 0.03 1.0 ± 0.4 126 GNGTS 2014 S essione 1.2