长周期地震动盆地效应表征模型的数值模拟

Studies have shown that long-period ground motions can be amplified due to basin structure, the amplification effects generate such as the amplitude increased, the duration lengthened. The basin effects of ground motions are extremely detrimental to engineering structures of long natural vibration period, such as high-rise buildings and bridges. The number of high-rise buildings, urban road overpasses and other lifeline engineerings is increasing in many cities. It is a new demand on urban planning and construction. It needs special attention to the seismic safety of such works, especially in those cities situated in the basin regions. However, the basin effects of ground motions are rarely considered in the building code of China. Therefore, it is necessary to quantitatively study the basin effects of long-period ground motions in characterization models...The project intends to carry out the numerical simulation of long-period ground motions on basin effects, which uses previous developed by the applicant structure-preserving algorithm, symplectic discrete singular convolution differentiator (SDSCD), and uses far-field earthquake input. It will quantitatively study the impact of the basin model parameters to ground motions peak value, response spectrum and duration by constructing several basin models to obtain strength level of space-time changes on amplification effects. It will lay the foundation on proposing evaluation method to meet the needs of engineerings for long-period ground motions on basin effects, to provide more reliable scientific basis for the seismic risk management of major projects.

研究表明，盆地结构对长周期地震动有明显的放大作用，会产生诸如幅值加大、持续时间变长等效应。这一地震动盆地效应对于高层建筑、桥梁之类的自振周期较长的工程结构体极为不利。当前在许多城市，高层建筑，城市道路立交桥及其它生命线工程日益增多。这对城市规划和工程建设提出新要求。尤其是在地处盆地内或边缘的城市，需要特别关注这类工程的地震安全性，而抗震设计规范中很少对这类地震动盆地效应做具体的规定。因此，定量研究表征模型长周期地震动盆地效应是非常必要的。本项目拟利用申请人先前发展的辛格式离散奇异褶积微分算子（SDSCD）保结构算法，设定远场大震的震源输入，开展受盆地结构影响的长周期地震动数值模拟工作。通过构建多种盆地模型，定量研究盆地模型参数对地震动峰值、反应谱和持时的影响规律，得到放大效应的时空强弱变化，为提出满足工程需要的长周期地震动盆地效应的评估方法奠定基础，为重大工程防震减灾提供更可靠的科学依据。

本项目的提出是基于工程地震学的实际需求，设定沉积盆地表征模型，在该模型上开展地震波场数值模拟，考虑地震动在盆地边缘以及盆地中央的放大效应。利用先前发展的辛格式离散奇异褶积微分算子（SDSCD）保结构算法模拟地震波场传播，设定远场大震的震源输入，采用完全匹配层（PML）吸收边界条件，开展受盆地结构影响的长周期地震动数值模拟工作。构建多种盆地表征模型，研究盆地模型参数对地震动峰值、反应谱和持续时间的影响规律，得到放大效应的时空强弱变化。以期为沉积盆地区域的地震动参数做出合理调整，并且对可能发生的地震灾情做出相应的预估预判奠定基础。盆地放大效应是由很多因素导致，与盆地沉积层厚度、盆地的几何形状以及盆地速度界面有关。沉积盆地为地震波提供了多条传播路径，会导致波从盆地边缘反射和在盆地中心汇聚，地震波在盆地的不同位置得到加强或削弱。数值模拟有助于我们定量地分析盆地效应的具体原因。. 按照项目任务书的要求，我们完成了以下研究工作。完善了数值模拟算法的震源输入模块，采用平面波入射方式；完善了吸收边界模块，采用PML边界条件；开展了长周期地震动的盆地效应数值模拟，考虑多种表征盆地结构模型，及不同角度的波动输入，获取了合成地震图、波场快照、地表峰值分布图（位移，速度及加速度）以及地表记录的频谱图。验证表征模型长周期地震动数值模拟评估盆地效应的有效性的研究工作，还有待进一步完善。