MASW Joint Analysis of Rayleigh and Love Waves for Site Characterization
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The determination of reliable shear-wave velocity vertical profiles using Multichannel Analysis of Surface Waves (MASW) has increased importantly for site characterisation studies due to their use in geotechnical studies and regulations, such as Eurocode 8, addressing urban assessment of the seismic hazard (López et al. 2022). The, so-to-speak, standard MASW approach is commonly based on the analysis of the vertical-component of Rayleigh waves, which can result in inaccurate and potentially erroneous interpretations by personal bias (Dal Moro, 2020). To overcome those potential issues, we present the joint analysis of different and independent multi-component data based on Rayleigh and Love waves to obtain 2D Vs sections for site characterization. Those seismic data were recorded using a landstreamer consisting of 8 triaxial 4.5 geophones with an interspacing of 7 meters. For data acquisition, an 8 kg-sledgehammer was employed as a seismic source with an offset of 14 meters. To generate Rayleigh waves the blows were given vertically on a plate, and for the Love waves the blows were given laterally on a horizontal wooden beam. A joint analysis of Rayleigh and Love waves data via full velocity spectrum analysis was conducted to generate their dispersion curves. This new approach enabled a proper identification of the fundamental and higher mode surface waves facilitating the reliable reconstruction of the subsurface Vs profiles through a robust joint inversion process. The MASW 1D Vs versus depth models were corroborated by the information obtained from boreholes. Thus, the main geological formations could be inferred from MAWS 2D Vs sections to a depth of 30 meters as well as the Vs30 parameter to perform a reliable seismic microzonation of the study area. This methodology provides a very-well constrained inversion procedure capable of providing a robust subsurface Vs model for site characterization.