VS30-based relationship for Chinese site classification

Abstract

Classification of engineering sites is essential when considering site conditions for seismic fortification in seismic design codes. However, because of different site classification methods, it is difficult for Chinese seismological and engineering communities to share site metadata (e.g., site classes) and relevant results with international communities. This issue also prevents the Chinese communities from utilizing well-established models based on the time-averaged shear wave velocity for the top 30 m (VS30). This study aims to close the gap and develop a consistent VS30-based site classification method. We first assemble the shear wave velocity (VS) profile data from various sites in China, Japan, and California to study the statistical characteristics of VS30 and the equivalent shear wave velocity (VSe, time-averaged within soil layers for ≤ 20 m, which is used in Chinese site classification). We then investigate the efficiency of site classification by VS30 and VSe alone, respectively. We find that the single VSe parameter is insufficient to distinguish different Chinese site classes, especially for site classes III and IV (which consider soil layers deeper than 20 m). In contrast, the VS30 parameter can effectively differentiate Chinese site classes from I0 to IV. A new VS30-based site classification method for Chinese sites is then developed. The boundaries of VS30 for each Chinese site class are determined by maximizing the rate of correctness. Our new VS30-based classification facilitates the connection of Chinese site classes with well-developed VS30-based models and site data sharing between Chinese and international scientific communities.