Evaluation of the thickness of alluvial sediments in the Catania plain through a geophysical and hydrogeological approach

A study aiming to evaluate the thickness of alluvial deposits in the north-eastern part of the Catania plain, was performed. This plain is one of the wider Sicilian alluvial plains and, in the study zone, it is formed by the sediments of the Simeto river. A combined idrogeological and geophysical approach was attempted in order to map the basement taking advantage from the relevant number of boreholes and geophysical surveys data available. It is indeed of primary importance to deduce the geometry of the alluvial deposits overlaying the quaternary clayey formation of the basement in order to evaluate the potential water resources of the area. Ambient noise measurements were performed using a mobile multi-component seismic station. The sites of field measurements were homogeneously distributed in the area taking into account the location of the available boreholes. The acquired data were processed through H/V spectral ratio technique. The resonance frequencies experimentally observed (fr) were related to the thickness of the overburden sediments of the alluvial plain through the well known relationship h = Vs/4 fr. It assumes that the transfer function of a sediment site is connected to the geometry and physical parameters of the subsurface layers, namely their thickness (h) and shear wave velocities (Vs), Moreover, in order to take into account the gradient of velocity with depth, the thickness of sedimentary cover was estimated using the relationship m = 96 f-1.388 with m and f being the mean thickness and the main peak in the H/V spectral ratio, respectively. The contouring of alluvial sediments thickness point out a tendency of the clayey basement to go towards increasing depth going from the NW to the SE part of the investigated area.