Land subsidence in Venice and Porto Corsini

Abstract

This paper is a contribution to t h e study of the problem<br />of subsidence in the Po delta and in t h e Venetian lagoon. We have compared<br />t h e d a t a supplied by tide gauges in Trieste, Venice and Porto Corsini (Fig. 1)<br />during t h e period 1896-1966, and in Genoa in t h e period 1894-1966. Although<br />d a t a were recorded in slightly different periods, these periods are sufficiently<br />overlapping to allow for a significant statistical comparison. We note t h a t the<br />movement of t h e annual mean sea level in Genoa and Trieste is greatly different<br />f r om t h a t of Porto Corsini and Venice and, in order to separate the component<br />due to eustatic effect f r om any possible movement of the coast, we calculate<br />t h e polynomial coefficients, t h a t best fit t h e real movements. Approximating<br />polinomials are of first degree for Genoa and Trieste and of second<br />degree for Porto Corsini and Venice. We have evaluate the coefficients of<br />crosscorrelation firstly on original d a t a and then subtracting f r om original d a ta<br />the best fit polinomials. The correlation is very significant and the trend is<br />similar in Trieste and Genoa. The power spectrum analysis with the direct<br />Fourier's method show long periods wich are shared by tide gauges. We<br />conclude estimating 1,35 mm/year the increase of the mean sea level for t he<br />eustatic effect in the Mediterranean 3,9 mm/year the subsidence in Porto<br />Corsini and 1,4 mm/year the subsidence in Venice.