Sensitivity of Trapped Stiff Layer in the Field Acquisition of Rayleigh Wave Using MASW

Vertical component acquisition of Rayleigh wave is the most widely used technique for multichannel analysis of surface wave (MASW). Dispersion imaging of the acquired field data is a critical step in determining the in-situ shear wave velocity profile by performing inversion analysis. The presence of trapped stiff or soft layers is common in real-world situations, and identifying such irregularities from dispersion images is crucial for an accurate inversion analysis. It is well known that the presence of a soft or low-velocity layer breaks the continuity of the fundamental mode and influences the higher modes, i.e., higher modes will carry more energy. However, the presence of a trapped stiff layer does not affect modes significantly in the dispersion image. In the present study, we have investigated the role of trapped stiff layers in the dispersion energy of the Rayleigh wave. The sensitivity of the trapped layers has been quantified by analyzing the Jacobian matrix. Further, the dispersion image of the corresponding synthetic earth profile is generated from the seismogram obtained by the standard staggered grid finite difference modeling. This study shows that it is difficult to capture the presence of a trapped stiff layer using only the vertical component MASW method.