Combined analysis of active and passive surface waves for 2D characterization of a landfill

Abstract

Active and passive surface wave methods have been effective tools for near-surface investigation. For the cases both the near-surface resolution and investigation depth are required, the incorporation of active and passive surface wave methods is necessary to measure the dispersion curve over a broad frequency band. In this work, we carry out the active and passive surface wave methods to characterize a landfill, mainly for delineating its base. Both active and passive surface wave data are collected using a linear array and the roll-along acquisition mode. To analyze the passive data, we use the seismic interferometry technique to generate the virtual source gather. According to the dispersion analysis results, the frequency bands for available phase velocity estimations of active and passive data are different but overlapped. We then employ the multiscale window analysis of surface waves (MWASW) method to extract several dispersion curves from active shot gather and passive virtual source gather. The use of the MWASW method is based on the consideration of heterogeneity in landfills. Once the dispersion curves are extracted, the two kinds of phase velocity data are combined to produce composite dispersion curves. By simultaneously inverting the composite dispersion curves of multisize spatial windows, a 2D shear-wave velocity (Vs) model is generated that shows a clear velocity contrast between the refuse and the underlying stratum at a depth around 5 m consistent with the result of five in-line boreholes. The successful investigation of refuse depth demonstrates that the combination of active and passive surface waves has a good ability to resolve the Vs model of landfills from surface to deep formations.