Performance of Different Transformation Techniques for MASW Data Processing Considering Various Site Conditions, Near-Field Effects, and Modal Separation

Multichannel analysis of surface waves (MASW) has received increasing attention in many disciplines in recent years. However, there are still issues with this method, which require further investigation. The most common issues include a potentially poor-resolution experimental dispersion image, near-field effects, and modal misidentification. Therefore, this paper examines the performance of four common wavefield transformation methods for MASW data processing. MASW measurements were performed using Rayleigh and Love waves at sites with different stratigraphy and wavefield conditions. For each site, dispersion curves were generated using the four transformation methods. For sites with a very shallow and highly variable bedrock depth with a high-frequency point of curvature (> 20 Hz), the phase shift (PS) method leads to a very poor-resolution dispersion image for approximately half the experimental datasets compared to other transformation methods. When a velocity reversal was present, the slant stack (tau p) method failed to resolve the dispersion image for frequencies associated with layers located below the velocity reversal layer. For sites where multiple modes are present, it was observed that the four transformation techniques have different sensitivities to higher modes. The cylindrical frequency domain beamformer (FDBF-cylindrical) method was determined to be the best method under most site conditions. This method allows for a stable, high-resolution dispersion image for different sites and noise conditions over a wide range of frequencies, and it mitigates the near-field effects by modeling a cylindrical wavefield. Overall, the best practice is to use the composite dispersion approach that combines all transformation methods or at least use two different transformation methods (FDBF-cylindrical and one of the other methods) to enhance the data quality, particularly for complex stratigraphy environments.