Deeper Vs profile constraining the dispersion curve with the ellipticity curve: A case study in Lower Tagus Valley, Portugal

Abstract

Shear wave velocity profile and bedrock depth are key parameters for seismic site response estimation and a reliable tool to evaluate liquefaction potential in soil deposits. They can be determined using in-situ geotechnical tests such as the seismic Cross-Hole (CH), seismic Cone Penetration Test (SCPT), seismic Dilatometer Test (SDMT), or through geophysical surface wave methods. The main advantages of surface wave methods are their non-invasive nature and the ability to characterize the shear wave velocity of the soil at a larger scale. However, the investigation depth in general is less than 20 m. Using the Rayleigh ellipticity curve to constrain the dispersion curve from active and/or passive measurements, deeper Vs-profile is obtained.In this study, the Vs profile of the soil at a site located over Lower Tagus alluvial Valley was obtained using different surface wave methods. For this purpose, ambient vibration measurements using a single three-component seismic station were made, to complement active and passive linear measurements. The Rayleigh wave ellipticity curve was computed from the single station recordings using the RayDec method and dispersion curves were estimated with the array recordings processed using f-k based methods: MASW, ReMi and conventional f-k method for non-linear array data. A joint inversion procedure was applied to the data and the results were compared with Vs profiles obtained from direct measurements with Cross-Hole and SDMT tests. The results show that considering the passive ellipticity curve in the joint inversion process with the dispersion curve, it is possible to obtain deeper and less scattered Vs profiles.