王伟,齐亚坤,熊文,王浩宇,李金宇,张晓庆. 2024. 地震作用下山体地形地震动偏振效应研究. 地震学报,46(4):1−14. doi: 10.11939/jass.20230166
引用本文: 王伟,齐亚坤,熊文,王浩宇,李金宇,张晓庆. 2024. 地震作用下山体地形地震动偏振效应研究. 地震学报,46(4):1−14. doi: 10.11939/jass.20230166
Wang W,Qi Y K,Xiong W,Wang H Y,Li J Y,Zhang X Q. 2024. Polarization effect on the ground motion of mountain topography under earthquake action. Acta Seismologica Sinica46(4):1−14. doi: 10.11939/jass.20230166
Citation: Wang W,Qi Y K,Xiong W,Wang H Y,Li J Y,Zhang X Q. 2024. Polarization effect on the ground motion of mountain topography under earthquake action. Acta Seismologica Sinica46(4):1−14. doi: 10.11939/jass.20230166

地震作用下山体地形地震动偏振效应研究

Polarization effect on the ground motion of mountain topography under earthquake action

  • 摘要: 基于汶川MS8.0地震后在窦圌山坡顶和坡脚测点获得的9次余震记录,进行基线校正、滤波处理,得到各余震记录的傅氏谱谱比及质点运动轨迹图,结果表明山体的自振频率具有多阶段性,其最大位移方位会出现在山体的横向或走向上,且山体存在偏振效应。将9次余震东西向和南北的水平向加速度时程以10°为单位进行分解得到324条新的时程曲线,基于分解合成后的时程记录,将坡顶与坡脚相同分解角度下的时程作比值,对其峰值加速度比和傅氏谱谱比进行分析,结果表明二者最大值所在的方位均与山体最大位移所在的方位相同。结合9次余震坡脚测点的傅氏谱分析可知,各输入地震动频率成分丰富的频段有所不同,低频段容易激发山体的低阶振型,导致山体在横向上发生偏振,高频段容易激发山体的高阶振型,导致山体在走向上发生偏振,当二者同时存在时,山体会同时产生低阶和高阶偏振效应。

     

    Abstract:
    A large number of earthquake site investigation and theoretical studies have shown that local site conditions have a significant effect on seismic damage and ground motion characteristics, which is usually manifested as amplification or reduction of ground motion. The mountain topographic effect of strong ground motion plays a great role in the antiseismic defense of major projects in mountainous areas. Currently, there are three main ways to study the topographic effect: topographic effect observation array, analytical analysis and numerical simulation calculation. The strong motion observation data from the array can directly reflect the characteristics caused by the complex terrain, and analysis results are more intuitive, real and reliable.
    Based on the nine aftershock records after the 2008 Wenchuan MS8.0 earthquake, the baseline-correction and filtration were carried out, and the Fourier spectral ratios and particle motion displacement trajectory diagrams were achieved.
    The average spectral ratio curve of the two horizontal records of 9 aftershocks has good consistency with the spectral ratio curve of a single aftershock. The natural frequency of the mountain is not unique, and the maximum spectral ratio will appear in different frequency bands, indicating a clear multi-order nature of the mountain vibration. 1.0−4.0 Hz is the lower-order vibration mode of the mountain, and 9.0−15.0 Hz is the higher-order vibration mode. There are significant differences in the source, magnitude, epicenter distance, and propagation path of each aftershock, but the spectral ratio curves of each aftershock have good consistency, indicating that the natural frequency of the mountain is related to factors such as the geometric shape of the mountain itself.
    The particle motion displacement trajectory diagrams show that under different earthquake input, the maximum displacement amplitude of the mountain vibration can appear in the transverse or longitudinal direction of the mountain.
    There exists the obvious polarization effect in the mountain vibration. The EW and NS acceleration records of the nine aftershocks were decomposed in 10° increments to obtain 324 new time histories. The amplification coefficients of the peak ground acceleration and the Fourier spectral ratio were analyzed for each decomposition angle. The orientation of the maximum peak acceleration amplification coefficient is basically the same as that of the maximum displacement amplitude of the mountain vibration, and the peak acceleration amplification coefficients of each decomposition angle have obvious polarization effects. The frequency bands of the nine aftershocks with the largest Fourier spectral ratios at different decomposition angles are relatively close to each other, and all of them are distributed in the frequency bands of 0.8−2.8 Hz, 7.8−10.2 Hz, and 11.5−16.0 Hz.
    However, the angular range in which the extreme values of the Fourier spectral ratios are located varies from one aftershock to another, with aftershocks 1, 3, 4, and 9. For the Fourier spectral ratio in the low frequency band of 0.8−2.8 Hz, the maximum amplitude appears in the range of 110°−160° i.e. transverse direction of the mountain; in the middle and high frequency bands of 7.8−10.2 Hz, the maximum amplitude appears in the range of 30°−60° i.e. longitudinal direction of the mountain.
    The seismic energy of the aftershocks 2, 5, 6, 7, and 8 is mainly concentrated in the mid- and high-frequency bands, and the maximum value of the spectral ratio is concentrated in the range of 30°−60° i.e. longitudinal direction of the mountain, which is more easily to stimulate of higher-order vibration modes of the mountain in this angular range, and the phenomenon is also roughly similar to that of the particle motion displacement trajectory diagrams and the orientation of polarization of the peak ground acceleration.
    Considering the Fourier spectrum analysis of the nine aftershock records at the foot of the slope, we can obtain that the frequency content is different. The low frequency band is easy to stimulate the lower-order vibration mode of the mountain that leads to polarization in the transverse direction; the high-order vibration mode is easily stimulated by the high-frequency band that leads to polarization in the longitudinal direction of the mountain; the mountain can produce both low-order and high-order polarization effects when the low and high frequency exist at the same time. The maximum displacement amplitude of the mountain under the action of different earthquakes will appear in the transverse and longitudinal direction of the mountain, which is closely related to the spectral characteristics of the input earthquake. In the seismic design of large-scale structures such as bridges, tunnels and hydropower stations across mountain areas, the polarization effect of the mountain topography should be given priority consideration.

     

/

返回文章
返回