A 100-Meter-Resolution Site-Condition Map of China Based on Surface Geology and Bedrock Depth

Accurate site classification maps are essential for updating the seismic ground motion parameter zoning map, as they account for the site effects. When field investigations are impractical, proxy-based methods (e.g., geological or topographic proxies) are commonly adopted to estimate VS30, a key parameter for characterizing site conditions. In this study, we compiled a nationwide borehole database comprising 10,650 profiles (82.02 % with depths >20 m) from research documents and technical reports. Using the site database, we developed a novel hybrid model for VS30 estimation by integrating surface geological category and subsurface bedrock depth as predictors. By combining 1:500,000-scale geological maps with a 100-m-resolution bedrock depth dataset, we produced a nationwide 100-m-resolution VS30 map that incorporates the regional variations in geological environments. Based on this map, we further established the 100-m-resolution Chinese site classification maps. Validation against borehole data demonstrates the national-scale applicability of our approach, with Chinese site classification accuracies of 79.38 % (Chinese site class II), 73.90 % (III) and 67.75 % (IV). Notably, in plain areas, our model outperformed slope-based methods in differentiating between II and III sites, as well as differentiating between National Earthquake Hazard Reduction Provision (NEHRP) site class C and D sites. Our proposed hybrid VS30 model advances the accuracy of proxy-based approaches for VS estimation. Concurrently, the developed nationwide site classification map offers valuable applications for seismic ground motion parameter zonation.