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The Applicability of Using HVSR to Evaluate Site-Effects, Verification of Vertical Arrays and Application for Stations in Western China

Session: How Well Can We Assess Site Effects So Far? [Poster]

Type: Poster

Date: 4/21/2021

Presentation Time: 03:45 PM Pacific

Description: 

The horizontal-to-vertical spectral ratio (HVSR) method is an efficient tool to evaluate the site-effects of engineering sites, but there seems no consensus whether its amplitude indicates the absolute amplification at the location of measurements. To further explore the applicability of using HVSR to evaluate site-effects, the HVSR and Empirical Transfer Function（ETF）analyses were performed on the S-wave recordings from two vertical borehole strong motion arrays: the Garner Valley Downhole Array in southern California and the KiK-net Rikuzentakata Vertical Array in Iwateken, Japan. The results show that the discrepancy between the HVSR and the ETF is mainly caused by the significant site response of the vertical component, thus, vertical incident P-waves are proposed to play an important role in the vertical amplification. The P-wave amplification is frequency-dependent. In the low-frequency range within f₀ (the fundamental frequency of the site), the effect of the vertical P-wave amplification is slight, this is why HVSR and ETF match in this frequency range. In the high-frequency range near 2 f₀ or larger, the P-wave amplification is obvious, which maybe explain the discrepancy between the HVSR and the ETF. These results indicate that the HVSR can be used to evaluate site-effects in relative low-frequency range within f₀. Based on upper analysis, site-effects of many strong motion stations in western China has been investigated, the results show that the HVSRs agree quite well with the observation in low-frequency range within f₀ even when velocity profiles change during severe earthquakes.

Presenting Author: Mianshui Rong

Student Presenter: No

Authors