Progressive Layer Stripping Analysis for HVSR Interpretation

The horizontal-to-vertical spectral ratio (HVSR) technique is widely used to determine site fundamental periods from ambient noise recordings, but relating the observed peak to a specific impedance contrast within layered soils remains challenging. This paper presents an enhanced implementation of hvstrip-progressive, a Python package for forward HVSR modelling under the diffuse-field assumption and systematic progressive layer stripping. The package computes theoretical HVSR curves from shear-wave velocity (Vs) profiles, iteratively removes the deepest finite layer and promotes the next layer to half-space, and tracks how the fundamental frequency and amplitude change with each step. Compared with previous implementations, the software now supports adaptive frequency scanning, rigorous model validation, and publication-quality visualizations. Using a synthetic seven-layer soil profile, we show that the fundamental peak shifts from 6.99 Hz to 23.45 Hz as layers are stripped and that the maximum impedance contrast of 1.46 at 17 m depth controls the resonance. The transparent workflow, reproducible outputs and open-source distribution make hvstrip-progressive a practical tool for seismic site characterization and microzonation studies.