1 Deeper Vs profile constraining the dispersion curve with the ellipticity 1 curve: a case study in Lower Tagus Valley, Portugal 2 3 Fátima Gouveia (1), António Viana da Fonseca (2) 4 Rui Carrilho Gomes (3) 5 Paula Teves-Costa (4) 6 (1) FEUP researcher under Liquefact project 7 (2) CONSTRUCTGEO, Faculdade de Engenharia da Universidade do Porto 8 (3) CERIS, Instituto Superior Técnico, Universidade de Lisboa 9 (4) Instituto D. Luiz, Faculdade de Ciências, Universidade de Lisboa 10 11 ABSTRACT 12 Shear wave velocity profile and bedrock depth are key parameters for seismic site response estimation 13 and a reliable tool to evaluate liquefaction potential in soil deposits. They can be determined using in- 14 situ geotechnical tests such as the seismic Cross-Hole (CH), seismic Cone Penetration Test (SCPT), 15 seismic Dilatometer Test (SDMT), or through geophysical surface wave methods. The main advantages 16 of surface wave methods are their non-invasive nature and the ability to characterize the shear wave 17 velocity of the soil at a larger scale. However, the investigation depth in general is less than 20 m. Using 18 the Rayleigh ellipticity curve to constrain the dispersion curve from active and/or passive measurements, 19 deeper Vs-profile is obtained. 20 In this study, the Vs profile of the soil at a site located over Lower Tagus alluvial Valley was obtained 21 using different surface wave methods. For this purpose, ambient vibration measurements using a single 22 three-component seismic station were made, to complement active and passive linear measurements. 23 The Rayleigh wave ellipticity curve was computed from the single station recordings using the RayDec 24 method and dispersion curves were estimated with the array recordings processed using f-k based 25