The analysis of Yunnan Dayao basin effect based on microtremor test and numerical simulation

Abstract

Microtremor tests and finite element numerical simulations were used to analyze the seismic ground motion effects of the Yunnan Dayao sedimentary basin. The results of the microtremor relative to the reference point spectral ratio (HS/HR) method showed that the spectral ratio curves of each observation point in Dayao basin show multipeak characteristics, indicating that the site consists of different soil layers; the predominant frequencies of each observation point mainly are 6~9 Hz in the basin and there are lots of differences in the predominant frequencies of different observation points, which indicate that the site stiffness of each observation point is different; the differences of spectral ratios between the east–west directions (EW) and the north–south directions (NS) reveal the site's anisotropy. The amplification coefficient characteristics of each observation point in the basin obtained by numerical simulation show that the predominant frequency is 6 ~ 9 Hz; the amplification coefficients of each observation point are different; the edge effect and the focusing effect amplify the seismic ground motion in the basin; the different amplification coefficients of the two sub‐basins reflect the significant effect of the basin soil layers' differences on the seismic ground motion, the site is softer and amplification coefficients are larger; the slope degree of basin edges significantly affects the seismic ground motion near the basins edge, the amplification coefficients of the slope steeper and amplification coefficients larger. This study demonstrates that the microtremor test spectral ratio (HS/HR) method has good reliability applied to the analysis of basin effect and combining the finite element numerical simulation method is more effective in revealing the basin effect mechanism.