GNGTS 2014 - Atti del 33° Convegno Nazionale

Many seismic events of variable magnitude and source coordinates have been recorded. S����� ����������� ��� ��� ���� ������ ������� �������� �������� �� ��� ������ ����� trong earthquakes and the most recent seismic sequence occurred in the region could contribute to the noise affecting the gravity records. The noise values estimated by ETERNA are 0.6 ���� nm/s 2 in the diurnal band and 0.3 ���� nm/s 2 in the semi-diurnal band. ��� ����� �� ��� The whole of the tidal spectral components obtained by the analysis represents, for the time being, a synthetic model of the gravity tide in the Calabrian area. �� ����� �� ������ ��� ���������� �� ��� ����� In order to obtain the parameters of the tidal field, the contribution of the Ocean Tide Load (OTL) to the gravity tide must be taken into account. Several models provided by the Onsala Space Observatory (http://www.oso.chalmers. se/~loading/) ���� ���� ���������� ����� have been considered here. It emerges that, at the station of Cosenza, the contributions of all the examined OTL models fall within the error limits of the results. Thus to compute the OTL effect, the recent EOT11a model (Savcenko and Bosch, 2008) has been chosen . The tidal analysis, carried out after the OTL effect was removed from the gravity records, yielded the “corrected” tidal parameters (A c , δ c = A c /A th and �α c , where A c and �α c are the computed amplitude and phase and A th is the amplitude of the astronomical tide) shown in Tab. 2 for only the waves significantly influenced by the OTL. Tab. 1 - Main components of the gravity tide at Cosenza station. Wave Amplitude ( nm/s 2 ) δ Phase (°) O 1 357.3 ± 0.7 1.173 ± 0.002 0.23 ± 0.08 P 1 163.9 ± 0.5 1.157 ± 0.003 0.5 ± 0.2 K 1 492.3 ± 0.5 1.150 ± 0.001 0.37± 0.06 M 2 538.4 ± 0.3 1.1986 ± 0.0006 0.99 ± 0.03 S 2 250.8 ± 0.2 1.200 ± 0.001 0.41 ± 0.06 Tab. 2 - Corrected tidal parameters and expected amplification factors of the main components of the tidal field at Cosenza station. Wave Ac ( nm/s 2 ) δ ± err Phase ± err (°) δ (DDW99/NH) O 1 358.7 1.177 ± 0.002 0.16± 0.08 1.15424 P 1 163.8 1.156 ± 0.003 0.4 ± 0.2 1.14915 K 1 491.9 1.149 ± 0.001 0.23 ± 0.06 1.13489 M 2 532.1 1.1847 ± 0.0006 0.25 ± 0.03 1.16172 S 2 247.7 1.185 ± 0.001 -0.004 ± 0.064 1.16172 Among several models describing the Earth’s response to the tidal field, twomodels have been proposed by Dehant et al. (1999): the elastic/hydrostatic model (DDW99/H) and the inelastic/ non hydrostatic model (DDW99/NH). As the estimated relative error of the calibration is of the order of 10 -3 it does not allow us to distinguish between the DDW99 elastic and inelastic models whose gravimetric factors differ of 0.0014. Taking into account the geodynamic features of the Southern Tyrrhenian basin, the DDW99/NH non-hydrostatic version of the model has been adopted as reference. In Tab. 2 the values of the amplification factor expected from the chosen model are also given. The ratio �δ M2 /δ O1 between the observed amplification factors pertinent to the main M 2 and O 1 lunar waves results 1.007±0.002, consistent with the value 1.006 expected by the model. ��� ����� �� ��� ���������� ���� ����������� ��� ������ �������� ����� ��� �������� The slope of the regression line correlating the values obtained using the computed tidal parameters and the corresponding values predicted by the model, results 1.002 ± 0.001 (r = 0.99), with a standard deviation � � � �� ���� σ � = ± 14 nm/s 2 . The deviation X between the observed amplitudes and phases of tidal waves and the corresponding values expected by the model can GNGTS 2014 S essione 1.2 125