GNGTS 2014 - Atti del 33° Convegno Nazionale

Three years of gravity continuous observations in the Calabria Arc System: a model of the gravity tide and the tidal field A. Albano 1 , A. Gervasi 1, 2 , I. Guerra 1 1 Dipartimento di Fisica, Università della Calabria, Arcavacata (CS), Italy 2 Istituto Nazionale di Geofisica e Vulcanologia, Centro Nazionale Terremoti, Roma, Italy Remarkable mass displacements of different origin and nature are currently active in the geological domain known as Calabrian-Peloritani Arc and in the adjacent Tyrrhenian and Ionian Seas (Fig. 1). ������������ ���������� ��� ������������� �������� ������ ���� ��� ������ ������ Geophysical, geological and archeological evidence exists that the Ionian coasts are interested by intense subsidence phenomena ����� ������ (e.g. Marino et al. , 2010; Minelli et al. , 2013; Stanley and Bernasconi, 2012). �������� ���� ���������� ������ ��� ����� ��������� ������ However, over geological times, the whole Calabrian region has been rapidly rising relatively to the sea level. The region can be subdivided into several blocks that move upwards with different mean vertical velocities, estimated in some areas up to about 2 mm/yr in the last 700,000 years (e.g. Sorriso-Valvo, 1993; Westaway, 1993; Antonioli et al. , 2006). Finally, as shown by the intermediate and deep local seismicity the subduction under the Tyrrhenian Sea is still active and should be taken into account, whatever its stage of development ����� ����� (e.g. Monna et al. , 2013; Piana Agostinetti et al. , 2009, and reference therein). Although ����� ���� � ������� ��� ��������� ������ �� ����� ������� � ������ �� �������� ������� since over a century the Calabrian region is going through a period of relative seismic quietness, its seismic hazard is at the highest levels in the Mediterranean basin due to several catastrophic earthquakes present in the historical records. In consideration of the mass movements described above, a gravity recording station was installed in Cosenza (Fig. 1) in order to contribute to the geophysical monitoring of this seismic region. The recorded signals could allow in fact to reveal tidal anomalies correlated with the difference between some local feature of the lithosphere and/or geodynamic activity and the corresponding characteristics of the models used to calculate the reference gravity tide. Albano et al. (2014) present and discuss the results of the analysis of less than two years of gravity and tilt records obtained in the Calabrian Arc System. Here we present an updating of the results presented there based on the analysis of observations overlapping those already considered and extended to a time interval of more than 3 years, a duration almost doubled. With the occasion we refer on an absolute gravity measurement and on three calibrations of the recording instrument carried out in the meanwhile. The records are accomplished at the station located at the Department of Physics of the University, Campus of Arcavacata, near Cosenza (φ = 39°.359005 N; λ = 16°.226858 E; h = 221 m asl; g = 9.8010671 ± 10 -7 m/s 2 ). The local value of the gravity was measured in 1994 by Istituto di Metrologia “Gustavo Colonnetti” of the Italian National Research Council (Cerutti and De Maria, 1994). The absolute station has been reoccupied in October 2013 by Istituto Nazionale di Ricerca Metrologica (Biolcati et al., 2013); the second value of g = 9.8010670 ± 10 -7 m/s 2 is consistent with the preceding one within the error limits, Fig. 1 – Map of the Calabria region and adjacent geological domains (after Orecchio et al. , 2011 modified). Circles: epicentres of earthquakes with mL ≥ 3.4 in the time interval 19860101 – 20140221 and depth ≥ 50 km (after ISIDe, Working Group (INGV, 2010), Italian Seismological Instrumental and parametric database; http://iside.rm.ingv . it); radius increases with depth up to the maximum of 644.4 km. Reversed triangles: GPS stations. Squares: cities GNGTS 2014 S essione 1.2 123