芦山MW6.8地震Newmark位移方向性研究

Directionality of Newmark displacement during the Lushan MW6.8 earthquake in 2013

摘要:

为研究2013年芦山 M_W6.8地震Newmark位移的方向性特征,使用震源区近场22个台站的强震动记录,利用Boore的改进方法对地震动进行投影,分析Newmark位移随方向性变化、最大值与最小值比值(Dn_max/Dn_min)和卓越方向(θ_max)等特征。得出以下结论:(1)Newmark位移随方向的变化存在明显的波峰和波谷,其最大值方向与最小值方向夹角在多数情况下处于近似垂直的关系。(2)Dn_max/Dn_min随着临界加速度(a_c)的增大而增大;a_c较大时,Dn_max/Dn_min随断层距的增大逐渐增大;此外,场地类型对Dn_max/Dn_min也有一定影响。(3)θ_max在断层两侧和同震位移方向存在较强的相关性,在断层两端与同震位移方向相关性较弱;θ_max与断层走向垂直方向(FN)的相关性不强;此外,θ_max不随a_c发生显著变化。(4)基于Arias烈度和考虑地震震级的Newmark位移经验模型对考虑方向性的Newmark位移的预测效果最好。

Abstract:

Using the strong motion records from 22 near-field stations in the focal area, the directionality of Newmark displacement during the 2013 Lushan M_W6.8 earthquake was investigated. The ground motions were projected using the modified Boore method to analyze the characteristics of Newmark displacement, including changes in directionality, the predominant direction (θ_max), and the ratio of maximum to minimum displacement values (Dn_max/Dn_min). Results show the following: (1) Newmark displacement exhibits distinct peaks and valleys as it changes with direction, and in most cases, the angle between the maximum and minimum directions is generally vertical. (2)Dn_max/Dn_min increases with critical acceleration (a_c); when a_c is large, Dn_max/Dn_min gradually increases with fault distance. In addition, the site type has a certain influence on Dn_max/Dn_min (3) A strong correlation exists between θ_max and the direction of coseismic displacement on both sides of the fault, but a weak correlation is observed on both ends of the fault. The correlation between θ_max and the vertical direction of the fault strike is weak, and θ_max does not notably change with a_c (4) The empirical model of Newmark displacement, which considers Arias intensity and earthquake magnitude, yields the best prediction effect of Newmark displacement when considering directionality.

Abstract:

Using the strong motion records from 22 near-field stations in the focal area, the directionality of Newmark displacement during the 2013 Lushan M_W6.8 earthquake was investigated. The ground motions were projected using the modified Boore method to analyze the characteristics of Newmark displacement, including changes in directionality, the predominant direction (θ_max), and the ratio of maximum to minimum displacement values (Dn_max/Dn_min). Results show the following: (1) Newmark displacement exhibits distinct peaks and valleys as it changes with direction, and in most cases, the angle between the maximum and minimum directions is generally vertical. (2)Dn_max/Dn_min increases with critical acceleration (a_c); when a_c is large, Dn_max/Dn_min gradually increases with fault distance. In addition, the site type has a certain influence on Dn_max/Dn_min (3) A strong correlation exists between θ_max and the direction of coseismic displacement on both sides of the fault, but a weak correlation is observed on both ends of the fault. The correlation between θ_max and the vertical direction of the fault strike is weak, and θ_max does not notably change with a_c (4) The empirical model of Newmark displacement, which considers Arias intensity and earthquake magnitude, yields the best prediction effect of Newmark displacement when considering directionality.