| Summary: | The estimate of the velocity of shear waves (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>V</mi><mi>s</mi></msub></semantics></math></inline-formula>) is essential in seismic engineering to characterize the dynamic response of soils. There are various direct methods to estimate the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>V</mi><mi>s</mi></msub></semantics></math></inline-formula>. The authors report the results of site characterization in Macerata (Italy), where they measured the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>V</mi><mi>s</mi></msub></semantics></math></inline-formula> using the seismic dilatometer in a 100 m deep borehole. The standard <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>V</mi><mi>s</mi></msub></semantics></math></inline-formula> estimation originates from the cross-correlation between the signals acquired by two geophones at increasing depths. This paper focuses on the estimate of the dependence of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>V</mi><mi>s</mi></msub></semantics></math></inline-formula> on the wavenumber. The dispersion curves reveal an unexpected hyperbolic dispersion curve typical of Lamb waves. Interestingly, the contribution of Lamb waves may be notable up to 100 m depth. The amplitude of surface waves decrease rapidly with depth; still, their influence may be essential up to depths considered unusual for standard geotechnical investigations, where their effect is generally neglected. Accordingly, these waves may bias the outcomes of the standard <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>V</mi><mi>s</mi></msub></semantics></math></inline-formula> estimations, which ignore frequency-dependent phenomena. The paper proposes an enhancement of the accepted procedure to estimate <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>V</mi><mi>s</mi></msub></semantics></math></inline-formula> and addresses the importance of Lamb waves in soil characterization.
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