Practical Aspects of Masw Inversion Using Varying Density

We use multi-channel analysis of surface waves (MASW) on seismic data to assess the practical impact of the assumed compressional-velocity and density parameters on the inverted shear-wave velocity results. The practical secondary-parameter impact evaluation was performed on data acquired in the arctic. The ice-sheet compressional-, shear-wave velocity and density variations with depth were available from laboratory and field measurement and served as reference for analyzing the MASW inversion. Presented MASW results demonstrate that the a-priori knowledge of density variation with depth can reduce the final inverted shear-wave velocity results typically by 6-7 % for the most of the middle layers from the velocity model and as much as 15% for some individual layers. After comparing the optimal parameter selection approach with the general theoretical recommendations it was concluded that using constant density leads to overestimation of shear-wave velocities by 7-8 %. Such an overestimation can lead to liquefaction underestimation at earthquake sites. Therefore, these findings can be of value for the engineering community interested in accurate shear-modulus site evaluation. Optimal density parameter selection can improve the reliability and quality of the final 2D Vs section. However, optimal processing MASW parameter selection, such as density variation with depth, can be best achieved using field tests and is the preferred approach over theoretical recommendations.