Estimating Site Characteristic Parameters of the Gobi Desert Region Using Seismic Noise

Abstract

In the Gobi desert region, the predominant frequency of the horizontal-to-vertical spectral ratio (HVSR) curve of seismic noise ( $f_{H/V}$ ) is typically above 3 Hz. However, most of the existing formulas for estimating cover thickness (H) based on $f_{H/V}$ are only applicable for $f_{H/V}$ values below 5 Hz. Therefore, new formulas that can accurately calculate H in this region are crucially needed. To this end, a case study was conducted where noise measurements were carried out in the Gobi region in China, as well as in the east and northeast regions of China. The HVSR curves and $f_{H/V}$ were calculated, and a formula that correlates $f_{H/V}$ with H was derived. In addition, formulas that correlate with Vs20 (average shear-wave velocities to depth 20 m) and Vs30 (average shear-wave velocities to depth 30 m) $f_{H/V}$ were fitted. The relationship between the site fundamental period ( $T_s$ ) and $T_{H/V}$ ( $1/f_{H/V}$ ) was also investigated. Finally, by using all of the noise measurements and applying the derived relationships, a method for rapidly measuring the site type was proposed. The results showed that the equation for calculating H in this paper is highly reliable, with relative errors less than 30% compared to other researchers. The correlation between $f_{H/V}$ and Vs30 was higher than that between $f_{H/V}$ and Vs20. The accuracy rate of the proposed method for fast identification of ground types was greater than 80%.