A Novel Soil Profile Standardization Technique with XGBoost Framework for Accurate Surface Wave Inversion

Abstract

The inversion of surface wave dispersion curves poses significant challenges due to the non-uniqueness, nonlinear, & ill-posed nature of the problem. Local search methods get trapped in suboptimal minima, whereas global search methods are computationally intensive. The CPU time becomes challenging when dealing with a large number of traces, such as 2D/3D surface wave surveys or DAS surveys. Several attempts have been made to perform inversion using machine learning to improve accuracy and reduce CPU times. Current machine learning methods rely on a fixed number of soil layers in the training dataset to maintain a consistent output size, limiting these models to predicting only a narrow range of soil profiles. Consequently, no single machine learning model can effectively predict soil profiles with a wide range of shear wave velocities and varying numbers of layers. The present study introduces a novel soil profile standardization technique and proposes a regression-based XGBoost algorithm to efficiently estimate shear wave velocity profiles for stratified media with a varying number of layers. The proposed model is trained using 10 million synthetic soil profiles. This extensive dataset enables our XGBoost model to learn effectively across a wide range of shear wave velocities. Additionally, the study proposes constraints on the differences in shear wave velocities between consecutive layers and on their ratio with layer thickness, preventing the formation of unrealistic layers and ensuring the predictive model reflects real-world conditions. The effectiveness of our proposed algorithm is demonstrated by adopting a wide range of soil profiles from published literature and comparing the results with traditional inversion methods. The model performs well in a wide range of S-wave velocities and can accurately capture any number of layers of the soil profile during the inversion process