Comparison of Different Site Classification Methods Based on Statistical Analysis of Strong Ground Motion Records

The one-index site classification based on the equivalent shear wave velocity of rock and soil layers within a specified depth as a control parameter, and the two-index site classification based on the equivalent shear wave velocity of soil layers within a specified depth and the thickness of overlying soil layers as control parameters, are the two major categories of site classification methods. The applicability and rationality of the two categories of methods have consistently been focal points of attention and discussion within the engineering community. The primary purpose of engineering site classification is to judiciously consider the site effect on strong motion to determine seismic design parameters for construction projects. The degree of consistency in the spectral characteristics of strong motion records within the same classified site stands out as the most effective criterion for elucidating the rationality of site classification methods. Utilizing strong motion records from the Japanese strong-motion seismograph network KiK-net and related site borehole data of the observation stations, statistical analysis was conducted to delve into the distinctions and merits of existing site classification methods. Initially, the site classification of the observation stations was carried out using site classification methods specified in seismic design codes from countries such as China, the United States, and Japan, and the collected strong motion records were grouped accordingly. Subsequently, statistical analyses of acceleration response spectra, including peak acceleration, were performed for ground motion acceleration records from the observation stations with a same site class specially for different site classification methods. The study also scrutinized the consistency of acceleration response spectra for strong motion records from the observation stations with a same site class across various site classification methods through statistical residual analysis. The research findings reveal that, among the site classification methods studied, the site classification method of the Chinese seismic design code, a two-index site classification method based on the equivalent shear wave velocity of soil layers within a 20-meter depth and the thickness of the overlying soil layers as control parameters, is deemed the optimal method.