Regional sediment thickness mapping via microtremor HVSR spatial variability

Due to its simplicity and cost-effectiveness, the microtremor Horizontal-to-Vertical Spectral Ratio method is widely used for estimating site-specific fundamental frequencies and sediment thicknesses. However, most existing applications estimate sediment thickness site-by-site, overlooking the spatial variability of microtremor HVSR frequencies (\(\:{f}_{mHVSR}\)). This study leverages the spatial correlation of \(\:{f}_{mHVSR}\)​ to develop a regional sediment thickness mapping approach. Using microtremor HVSR data from 22 sites across a study area spanning several hundred square kilometers, where sediment thickness ranges from a few meters to several tens of meters, this study employs geostatistical methods to analyze the spatial variability of \(\:{f}_{mHVSR}\). Sediment thickness estimates from the proposed and existing methods are compared with measured values for validation. Finally, based on the HVSR and sediment thickness data from these sites, a regional sediment thickness model for the study area was developed. The results show that the spatial correlation range of \(\:{f}_{mHVSR}\) in the study area is 5.07 km, highlighting its regional variability. Compared to existing methods, the proposed approach not only significantly reduces prediction errors but also ensures a more uniform spatial distribution of errors. Furthermore, by comparing with the measured sediment thickness from 80 boreholes, the regional sediment thickness model developed in this study accurately captures the spatial variation characteristics of sediment thickness within the study area. Additionally, we propose an optimal strategy for selecting reference boreholes, recommending the one whose \(\:{f}_{mHVSR}\)​ most closely matches the detection site within the spatial correlation range. By integrating \(\:{f}_{mHVSR}\) spatial variability, this study providing a more precise and efficient method for sediment thickness mapping framework.