Gravity tidal field in an active geodynamic area of southern Italy: the Calabrian Arc system.

Albano A., Carbone V.

Comunicazione
IV - Geofisica e fisica dell'ambiente
GSSI Ex ISEF - Aula D - Mercoledì 25 h 10:00 - 13:00
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Four years of gravity records, spanning the time window May 2011 - April 2015 obtained at the Department of Physics of the Università della Calabria (Southern Italy), are analysed and discussed. Calabria is a site of considerable seismic activity related to the on going evolution of the Calabrian Arc system characterized by a complex lithospheric structure. As several catastrophic earthquakes occurred in the region the seismic hazard is at the highest levels in the Mediterranean basin. The gravity recorded signals should allow to detect tidal anomalies, possibly correlated with the difference between some local feature of the lithosphere, or geodynamic activity, and the corresponding characteristics of the DDW99/NH Earth's model, adopted here for reference to calculate the reference gravity tide. A reliable model of the gravity tide is essential for the accurate processing of the high precision absolute and relative measurements of the gravity field and to detect in the gravity signals possible components correlated to major seismic activity. The contributions to the gravity of the Ocean Tide Load (OTL), and of the Length of Day (LOD) and Polar Motion (PM) changes, have been accounted for in the computation of the amplitude and phase of the spectral components of the tidal field. The contribution of the atmospheric pressure changes has been also taken into account. The most widespread DDW99/NH Earth's model fits the obtained results well enough. Finally the residual tidal vectors, as deviations of the spectral components of the observed tidal field from the reference model, have been computed. The meaning of the tidal residual vectors is still debated, ranging from the conjectured existence of correlations with local deviations of some lithospheric parameters from the reference model, to the opposite conclusions that the residual vectors chiefly depend on the instrumental noise and on the inadequacy of the existing OTL models. Our first results shows that, in the monitored region, a clear significant anomaly of the tidal residual vectors, undoubtedly ascribable to the complex structure of the local lithosphere, is not so evident.

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