Ensuring very shallow-water sediment properties: case study from Capo Granitola harbour, Sicily (Italy)

We present high-resolution Vp models of
the Capo Granitola harbor, Sicily (Italy) obtained by first
arrival traveltime tomography. Seismic data were collected
along four hydrophone arrays on the sea-bottom and via
a Watergun as seismic source, in order to plan dredging
operations in the harbor. Using a hydrophone spacing of
2.5 m and shot spacing of 5 m, very high resolution quality
data were recorded. Seismic tomography expands existing
knowledge of the harbour subsoil with a penetration of
about 20 m, illuminating the Lower Pleistocene bedrock
(Marsala calcarenites) that corresponds to high-Vp regions
(Vp > 4.5 km/s). Low Vp (1.8-4.5 km/s) deposits belonging
to terraced calcarenites (Upper Pleistocene in age) are
also well imaged; they are about 8 m thick and lie below
loose sand deposits (Vp = 1.5 km/s). The substratum has an
articulated morphology; Vp images unravel small steps in
the basement probably related to structural discontinuities
(e.g., faults). Processing data with 3D techniques enables
images of the structure and the thickness of the lithotypes
to be reconstructed, thus leading to large-scale, realistic
estimates of the total quantity of material to be excavated
or dredged. Tomographic profiles permit clear discrimination
of the soft sediment above the basement and thus allow
the determination of the total volume of sediment above the
seismic bedrock, estimated at about 265,000 m3.[object Object]