莫霍反射效应对俯冲带浅地壳地震动衰减模型的影响研究

Influence of Moho reflection on ground-motion prediction equations of shallow crustal earthquakes in subduction zone

为探究莫霍反射效应对俯冲带地区浅地壳地震动衰减模型的影响,基于日本KiK-net和K-NET台阵的4 014条水平向浅地壳强震记录,分别建立没有考虑莫霍反射效应的地震动衰减模型Ⅰ和考虑莫霍反射效应的地震动衰减模型Ⅱ,并对比分析了2个模型的残差分布、拟合优度及预测结果。研究发现,莫霍反射的影响降低了浅地壳地震某一距离范围内地震波的几何衰减率,采用三段线性几何衰减函数考虑莫霍反射效应的影响,明显改善了模型准确性;采用三段线性几何衰减函数的地震动衰减模型的最大对数似然值有大幅度增加,拟合优度明显提高;2个模型的预测反应谱在多数谱周期点上均存在显著差异,采用三段线性几何衰减函数的地震动衰减模型的预测反应谱在各距离分段上的变化趋势利于提高模型预测结果。结果表明,在俯冲带浅地壳地震动衰减模型研究中,可以采用一个相对简单的三段线性几何衰减函数考虑莫霍反射引起的复杂路径效应的影响,模型可靠度和标准差均显著提高。

To investigate the influence of Moho reflection on ground-motion prediction equations for shallow crustal earthquakes in subduction zones,4014 records from shallow crustal earthquakes in Japan obtained by the KiK-net and K-NET strong-motion networks were collected. Two ground-motion prediction equations for shallow crustal earthquakes,Model Ⅰ without accounting for the Moho reflection effect and Model Ⅱ including this effect,were developed and the differences in the residual distributions,goodness-of-fit parameter,and the predicted results between the two models were evaluated. These results suggest that the Moho reflection effect reduces the geometric attenuation rates of the seismic waves in a certain distance range for shallow crustal earthquakes,and using a trilinear geometric attenuation function accounting for the Moho reflection effect improves the overall modeling significantly. The maximum log-likelihood of the model with a trilinear geometric attenuation function also increases significantly,i.e.,the overall goodness-of-fit is improved. The predicted response spectra by these two models differ significantly at most spectral periods,and the model with the trilinear geometric attenuation function is improved at each distance segment. These results show that the complex path effect caused by Moho reflection can be accounted by using a relatively simple trilinear geometric attenuation function and the model predictions and the various standard deviations can be improved for the shallow crustal earthquakes in the subduction zone.