Regional mapping of sediment thickness using microtremor HVSR spatial variability

Abstract

The microtremor Horizontal-to-Vertical Spectral Ratio (HVSR) method is widely adopted for estimating site fundamental frequency ( $$\:{f}_{0}$$ ) and sediment thickness due to its simplicity and cost-effectiveness. However, current applications typically estimate sediment thickness individually per site, neglecting the spatial variability of microtremor HVSR frequencies ( $$\:{f}_{mHVSR}$$ ). This study develops a regional sediment thickness mapping method by leveraging $$\:{f}_{mHVSR}\:$$ spatial correlations. Using HVSR data from 22 sites across a study area covering hundreds of square kilometers (sediment thickness range: several meters to tens of meters), we analyze $$\:{f}_{mHVSR}$$ spatial variability through geostatistical methods. Validation compares sediment thickness estimates from proposed and existing methods against measurements. Finally, we construct a regional sediment thickness model based on site HVSR and thickness data. Results reveal a 5.07 km spatial correlation range for $$\:{f}_{mHVSR}$$ , demonstrating its regional variability. The proposed method significantly reduces prediction errors compared to existing approaches and achieves more uniform error spatial distribution. Comparison with 80 borehole measurements confirms the model’s accurate representation of sediment thickness spatial variations. We further present an optimal reference borehole selection strategy: choosing the borehole with $$\:{f}_{mHVSR}$$ closest to the target site within the spatial correlation range. By incorporating $$\:{f}_{mHVSR}$$ spatial variability, this study establishes a more precise and efficient sediment thickness mapping framework.