【作者】 常莹；

【导师】 俞言祥； 周红；

【作者基本信息】 中国地震局地球物理研究所 ， 防灾减灾工程及防护工程， 2011， 硕士

【摘要】 在工程地震学中,特别着重研究较大地震或大地震产生的宽频地震波,因为这些波是地震引起建筑物与结构物破坏的主要原因,合理有效的近场强地震动预测有利于减轻未来大地震所造成的灾害以及帮助重大工程的抗震设计和地震危险性分析。论文介绍比较了现有的近断层强地震动估计的研究方法,主要有确定性方法(包括理论和经验格林函数方法),随机方法和混合法。介绍了三种方法的理论基础,分析比较了各种方法的特点和优势。目前,理论格林函数方法主要用于计算低频(<1Hz)地震波,受计算条件限制,很少应用于计算高频地震波；高频(>1Hz)地震动常用经验格林函数法或随机方法。经验格林函数法要求有相同震源机制的、高信噪比的小震记录；随机方法没有考虑实际地壳速度结构对传播中波的影响,对低频段地震动模拟不够准确。本文通过计算理论格林函数,尝试采用分解给定的震源时间函数的方法来模拟宽频带(0.1~10Hz)强地面运动,即：采用分级离散断层面和分解断层面破裂单元上升时间的方法,来模拟断层破裂的细节过程,增加震源时间函数中的高频信号,进而得到宽频带地震图。这种方法避免了对地震记录丰富程度和准确性的依赖,同时可以保证结果体现明确的体波和面波到时,有利于在缺少或者没有强地震动记录数据的地区中使用。本文以2000年9月3日的美国Yountville地震(Mw5.0)为算例,进行了近场强地震动模拟计算。首先根据断层破裂面积、断层尺度及平均滑动与地震矩的关系经验半经验关系式,确定模拟的断层模型。模拟计算了近断层50km内的10个台站的地震图,比较了模拟结果和观测记录的加速度时程和傅里叶振幅谱,分析了加速度时程的特点,通过傅里叶振幅谱的对比结果,看到改变输入震源时间函数的新确定性方法可以模拟到0.1~10Hz宽频段地震动。作为对大地震近断层强地震动模拟的应用,模拟计算了汶川地震在8个地震观测台的地震动,将模拟结果和观测记录进行了加速度时程曲线和傅里叶振幅谱的对比分析。对比结果显示,模拟估计的地震动加速度峰值和持续时间与观测记录的数据基本在±50%的精度范围内相同,傅里叶振幅谱显示模拟结果有得到10Hz左右的高频成分,四川盆地中的台站模拟结果高频衰减比观测记录要快,原因是模拟过程没有考虑场地效应,在地形复杂地区的强地震动模拟还是要综合考虑震源、传播路径和场地的影响。研究结果表明此改变震源输入的确定性方法可应用于模拟近断层宽频强地面运动。同时为反应近断层附近的地震动特点,计算了断层距为20km的两条测线,模拟结果显示出地震动的方向性效应和上下盘效应；进一步计算了近断层200km范围内的PGA分布图,比较地震烈度分布图,模拟结果合理显示了汶川地震动的分布特征。更多还原

【Abstract】 In the intercrosss area of engineering and earth science, study on broadband ground motions generated by strong or great earthquake is a key research field because these waves is the main reason to cause the damage and collapse of buildings and other engineering structures. A good and efficient estimation method of the ground motion is usful to reduce the damage of future strong earthquake and help to do the resisting earthquake design and probabilistic seismic hazard analysis for the major projects. Earthquake researchers and earthquake workers have proposed several methods for the near fault ground motion synthesis. This article introduces the mainly three methods such as the deterministric method(including theoretical and empirical green function), the stochastic method and the hybrid broadband frequency strong ground motion simulation technique. The theoretical fundament of the methods have been explained and compared their characteristic and advantage. For now, the theoretical green function is mainly used to simulate the low frequencies (0.1-1Hz) due to the computation conditions. The high frequencies(1.0-10Hz) can be simulated by empirical green function method or stochastic method. The empirical green function method needs some some earthquake records which have high signal-to-noise ratio the same source mechanism as the simulated target earthquake. The stochastic, bandlimited, white-noise synthetics have not considered the propagation in the earth materials and the accuracy of long period earthquake waves.In this paper, a discreting model of source function based on kinematics is adopted for predicting near field strong ground motion in broadband frequencies (0.1-10Hz) using theoretical elastic-wave-propagation sythetics in multi-layered half-space media. The high frequency components can be calculated by keeping the high frequency signal of the source functions when we discrete the fault plane in second order and disintegrate the rise time of each fault element. Theoretical elastic-wave-propagation sythetics introduce proper seismic-phase arrivals of body waves and surface waves and reduce the dependence with the earthquake records’richness and accuracy.In order to illustrate the reliability and praeticability of the changed source function theoretical green function method developed by this paper,2000 Mw5.0 Yountville, California, Earthquak is taken as an example. Firstly, according to the relation between the rupture area, the longth and width of the fault, average slip and the earthquake moment magnitude, we determine the fault model. Then we calculate 10 stations ground motion near the fault (the distance from station to epicenter<50km). Acceleration time histries and the frequency spectra were compared with those records observed at the same stations during the shock. The results show that the acceleration frequency spectra from the discreted source model of the paper with theoretical green function synthesis can be predict well. And also some difference in shape of acceleration time history envelops.As another test of the application for the great earthquake near fault strong ground motion simulation, we simulate ground motions of Wenchuan earthquake in 8 selected stations located near the fault. The results show overall agreement on the acceleration histries, duration within±50% tolerance between the simulated and observed acceleration. The simulated Fourier spectrum has the components as high as 10Hz. The simulated Fourier spectrums at the stations in the Sichuan basin attenuate faster than the observed because the method has not considered site effect. The strong ground motion simulation should consider all the source, propagation path and site effect in the complicated topography. The results indicate that the deterministic method changing input source functions can be applied to simulate the near-fault strong ground motion in the broadband frequencies.Then Calculate the velocity histries on two survey line 20km from the fault line to learn more about the characteristic of the near fault ground motion. These results show the effects of hanging wall and the forward directivity. Futhermore, the PGA distribution on the areas within 200km away from the fault displays the generally influence regions.更多还原