基于多尺度分析方法的近断层地震动特性分析

On near-fault ground motion characteristics through multi-scale method

近断层长周期地震动是一类较特殊的破坏性地震动．为了深入探讨近断层地震动的低频分量组成及其脉冲特性，基于小波理论中的多尺度分析方法提出了一种地震动分量分解方法，据此可将一条地震动分解成频率各不相同的多条分量．首先从频域、时域以及动态响应三个方面阐述了该分解方法的有效性和精确性．进而采用这种方法对近期12次大地震中的53条典型近断层地震动进行了分解，共获得266条地震动分量．分析了近断层地震动中的长周期分量随场地、断层距等影响因素的变化特征；再以卓越分量作为最大脉冲的简化模型，探讨了速度幅值和脉冲周期随震级、断层距的变化关系．结果表明：近断层长周期地震动主要由周期为0．2～2S的分量组成；近断层土层场地地震动中的长周期分量比岩石场地多；在O～15km的近断层区域，随断层距的增加，地震动中长周期分量的比重明显减小；卓越分量的速度幅值PGU约为原始地震动速度幅值PGV的0．6倍，且两者之间具有明显的线性关系；PGVp随断层距的增大而减小，随震级的增大而增大；卓越分量周期Tp随震级的增大呈对数线性增大趋势．

The near fault ground motion with long period is a special destructive ground motion. For further research on the composition of low-frequency components and their pulse characteristics, a decomposition method of ground motion components based on multi-scale analysis method in wavelet theory was proposed. Accordingly, a complete ground motion can be decomposed into multiple components with different frequencies. First, we elaborated the validity and accuracy of the decomposition method in three aspects, which are the frequency domain, time domain and the dynamic response. Second, decomposed 53 typical near-fault ground motions from 12 recent major earthquakes through this method, and obtained a total of 266 ground motion components. Third, quantitatively analyzed the variation of the long period components in near fault ground motions with the impact factors of site and rupture distance. Last, used predominant component as the simplified model of the dominant pulse, and analyzed the variation of the velocity amplitude and pulse period with magnitude, rupture distance factors. The results showthat 0.2-2 s component is the main ingredient of near-fault ground motions; There are more long-period components in soil ground motions than the rocks; In near-fault area, 0~ 15 km, with the rupture distance increasing the long period components＇ proportion decreases; PGV,,, the velocity amplitude of predominant component, is about 0. 6 times of PGV, the velocity amplitude of original ground motion, and there is a clear linear relation between them. With the rupture distance increasing PGVp decreases, and will be larger in great earthquake. The pulse period Tp increases logarithmically linearly with the moment magnitude.