Site Effects of Linear Method and Modified Horizontal-to-Vertical Spectral Ratio
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摘要:
为进一步研究工程地震动场地效应的影响，基于水平垂直谱比法（HVSR）、线性反演法2种经验方法对四川强震区地震动场地效应进行对比分析. 首先，依据震级、台站、震中距离等因素挑选出汶川地震余震中由17个强震动台站捕获的233组强震动波形；其次，基于龙门山地区铰链三段式衰减模型，采用线性反演法估计S波的品质因子
Q s，同时应用旋转HVSR、多向HVSR 2种方法解释了地震波传播中方位角对HVSR场地效应的影响机制；最后，分析了线性反演法与HVSR法计算的场地效应产生差异性的原因，在此基础上提出了改进的HVSR法以提高场地效应评估的准确性. 研究结果发现：该区域S波的品质因子与频率相关，且在0.4～20.0 Hz内近似等于199.2f 0.8 （f 为频率）；HVSR的结果具有优势方向，随着方位角的改变，场地效应会在某一角度突然增大，与场地土层的各向异性有关；竖向地震动的放大，即场地土层、工程基岩或中深部硬岩层耦合形成的竖向场地效应，是HVSR法与线性反演法产生差异的主要原因.Abstract:In order to further study the influence of site effects from engineering ground motion, a comparative analysis of site effects from ground motion in the Sichuan strong earthquake area was carried out based on two empirical methods, namely, horizontal-to-vertical spectral ratio (HVSR) and linear inversion. Firstly, 233 sets of strong motion waveforms captured by 17 strong motion stations during the aftershocks of the Wenchuan Earthquake were selected based on the magnitude, station, distance from the epicenter, and other factors. Second, the linear inversion method was used to estimate the quality factor
Q s of the S-wave based on the hinged three-stage attenuation model in the Longmenshan area. Meanwhile, two methods, rotational HVSR and multidirectional HVSR, were applied to explain the mechanism of the site effect of azimuthal angle on HVSR in seismic wave propagation. Finally, the possible reasons for the variability of the site effects calculated by the linear inversion and HVSR methods were analyzed, based on which an improved HVSR method was proposed to improve the accuracy of the site effect assessment. The results show that the quality factor of the S-wave in the area is frequency-dependent and approximately equals to 199.2f 0.8 in the range of 0.4–20.0 Hz. The results of HVSR may have a certain dominant direction, and the site effect may increase suddenly at a certain angle with the change of the azimuthal angle, which may be related to the anisotropy of the soil layer at the site. The amplification of vertical ground motion, i.e., the vertical site effect formed by the coupling of soil layer at the site, engineered bedrock, or middle and deep hard rock layers, is the main reason for the difference between HVSR and linear inversion methods.-
Key words:
- site effects /
- Qs value /
- linear inversion /
- HVSR method /
- azimuthal angle
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图 8 HVSR与线性反演法场地效应的对比
Figure 8. Comparison of site effects between HVSR and linear inversion
图 9 线性反演计算的17个台站竖向场地效应的结果
Figure 9. Results of vertical site effects calculated by linear inversion for 17 stations
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