A 30 Arcsec Resolution VS30 Map for Mainland China Using Refined Topographic Slope-Based Cokriging (SCK) Model

ABSTRACT In 2022, we proposed a VS30 proxy model based on the Cokriging method, integrating local VS30 measurements with topographic slope data (SCK model, Zhou et al., 2022). Utilizing this model, a VS30 map for mainland China was developed based on 7797 local boreholes. However, the initial VS30 map was produced with a coarse grid resolution of 360 arcsec and did not comprehensively cover mainland China due to sparse distribution of boreholes in certain areas. In this study, we refined the SCK model by explicitly accounting for the influence of surrounding topographic slopes, incorporating more distant VS30 measurements, and improving the spatial distribution of VS30 measurements used in the model calculation. Tests based on virtual cases were conducted to evaluate the characteristics of the refined SCK model. In addition, 142 VS30 measurements from strong-motion stations in western China were added to enhance spatial coverage and model accuracy in these regions. Employing the refined SCK model and the expanded VS30 data set, a new VS30 map for mainland China was generated. This updated map features a higher grid resolution of 30 arcsec and covers the entirety of mainland China, showing reduced estimation errors and improved continuity. Comparisons with the U.S. Geological Survey Global VS30 Mosaic indicate that the results from the refined SCK model are more reasonable, as evidenced by local topography, VS profiles, lithologic profiles, and geology map, which better capture the impact of local geomorphological differences and climatic conditions on VS30 values.