Analysis of Shallow Velocity Characteristics Using Vs Inversion Constrained by Seismic Reflection

Understanding how seismic waves propagate through the subsurface is crucial for evaluating potential impacts on buildings and infrastructure. Velocity profiles provide essential information for seismic hazard mitigation, including estimation of average shear-wave velocity (i.e., V_S30), assessment of nonlinear site effects, and numerical wave propagation simulations. These profiles can be obtained using various techniques, such as P-S logging, multiple-channel analysis of surface waves (MASW), and microtremor array analysis. However, differences in resolution and investigation depth among these methods can complicate their integration for geophysical and engineering applications.

In this study, we combine results derived from seismic reflection and microtremor array measurements (MAMs) to construct layered velocity models. Layered P-wave velocity (V_p) profiles are derived from seismic-reflection velocity analysis. The Dix equation is used to convert root-mean-square velocities into interval velocities for each layer. The depths of P-wave velocity interfaces are then used as constraints for S-wave velocity (V_s) inversion, performed using the software HV-Inv (García-Jerez et al., 2016). Monte Carlo sampling and the simplex downhill method are employed to generate ensembles of V_s, V_p, and density profiles, which are evaluated by Rayleigh-wave phase-velocity dispersion curves inversion.

The resulting layered V_p and V_s models enable investigation of the relationships between V_p, V_s, V_p/V_s, and Poisson’s ratio, as well as the factors controlling the variations in the shallow subsurface. These studies aim to provide a robust framework for integrating P-wave and S-wave velocity profiles to characterize shallow seismic site conditions.