An Automatic Surface Wave Analysis Approach for the quasi-3D Vs estimation in engineering applications

Summary The importance of shear-wave velocity as a characterization parameter in geotechnical standards is great, since it is related to the elastic shear modulus and can be directly measured by geophysical methods. In this study, a well-adapted methodology to geotechnical investigations is proposed, in order to achieve the automatic frequency-dependent mapping of the Rayleigh waves group and phase velocity, throughout an active seismic network. The newly created Common-Mid-Point (CMP) Cross-Correlation (CC) analysis technique is based on partitioning the different wave propagation directions, weighting the CCs' frequency-time analysis around one wavelength and stacking the CMP frequency-velocity dispersion images. Then, virtual travel-times for all possible receiver pairs are generated from the azimuth-dependent results of the specific analysis and are inverted in a frequency-dependent tomographic framework. The proposed technique is put forward for the assessment of subsurface condition in a noisy urban area near the centre of Athens, in Greece. The major challenge has not to do only with the very difficult acquisition conditions of seismic data in respect to signal to noise ratio (S/N), but also with the effort to reveal the subsurface formation and its geotechnical properties, even under an existing building.