Shallow and in depth seismic testing in urban environment: A case study in Lisbon Miocene stiff soils using joint inversion of active and passive Rayleigh wave measurements

Abstract

The use of Surface Wave Methods for the characterization of the shear wave velocity profile of the soil has become increasingly attractive due to its non-invasive nature and its ability to provide information at a larger scale. Their main drawbacks are the non-uniqueness of the solution and high uncertainty of the results at higher depths. Its application in dense urban areas can be challenging due to the proximity to underground structures, high background noise level and space limitations. This paper describes a case study on the use of surface wave based methods on stiff soil in urban environment within a confined area located in Lisbon city, Portugal, surrounded by buildings and between an underground car park and the subway tunnel. The old building, built in the study area, was demolished for the construction of a new building with five basement floors. During this process, passive and active linear array and passive three-component single-station measurements were made at the surface level, before the works started, and at 2 deeper excavation levels. The results obtained using shallow and in depth measurements were compared, including HVSR and Rayleigh wave ellipticity curves and Vs profiles obtained through the conventional MASW method and through the joint inversion of both Rayleigh wave dispersion and ellipticity curves. A deeper Vs profile with low uncertainty was obtained through the joint analysis of Rayleigh wave dispersion and ellipticity curves, compatible with Vs profile obtained in depth.