A New Perspective on Surface HVSR Responses to Subsurface Anomalies Based on Full-Wavefield Simulations and Field Validation

Horizontal-to-Vertical Spectral Ratio (HVSR) analysis of ambient noise is widely used for near-surface characterization and underground anomaly detection. We revisit the assumption that single-station HVSR mainly reflects the structure beneath the receiver, using diffuse-field theory, three-dimensional full-wavefield simulations, and field experiments. Numerical results show that velocity anomalies can produce the strongest HVSR responses beside, rather than only above, the target. This sidelobe pattern is confirmed at an outcropped void on the SUSTech campus and is consistent with ambient-noise observations at an urban metro construction site.