华北地区厚沉积层对长周期地震动影响的数值模拟

The study of ground motion is a cross research field between earth science and engineering science. Theoretical seismologists are more concerned about propagation path and the effect of seismic focus, while engineering seismologists are more concerned with the ground effect. Studies have shown that the western Taiwan coastal plain is influenced by long-period ground motion from the 1999 Chi-Chi, Taiwan, earthquake, and engineering structures with natural vibration long-period are damaged by strong surface wave in the western coastal plain. The thick sediments in the western coastal plain are the main cause of the propagation of strong long-period ground motion. The thick sediments similar to in the western coastal plain also exist in northern China. ..It is necessary to research the effects of thick sediments to long-period ground motion in northern China. The numerical simulation of ground motion based on theoretical seismology is one of important means to study the ground motion. We will carry out the numerical simulation of long-period ground motion in northern China by using the existing tomographic imaging results of northern China to build underground medium model, and adopting finite fault source model for wave input. In the process of simulation, our previous developed structure-preserving algorithm, symplectic discrete singular convolution differentiator (SDSCD), is used to deal with seismic wave field propagation. Our purpose is to reveal the formation and propagation of long-period surface wave in thick sediments and grasp the amplification effect of long-period ground motion due to the thick sediments. It will lay the foundation on providing the reference for the value of the long-period spectrum during determining the ground motion parameters in seismic design.

地震动研究跨地球科学与工程科学两研究领域，理论地震学家更关心其传播路径与地震震源效应，工程地震学家更关心其场地效应。有研究表明，1999年台湾集集地震引发台湾西部滨海平原受长周期地震动影响严重，强面波对具有较长自振周期的工程结构造成破坏；台湾西部滨海平原厚沉积层是导致强烈长周期地震动传播的主要原因。华北地区存在与台湾西部滨海平原相似的厚沉积层。有必要研究华北地区厚沉积层对长周期地震动的影响。基于理论地震学的地震动数值模拟是研究地震动的手段之一。我们将借助华北地区已有的层析成像结果，建立地下构造模型，采用有限断层震源模型进行波动输入，开展长周期地震动数值模拟，其中的波场传播环节采用申请人先前发展的辛格式离散奇异褶积微分算子保结构算法。以此揭示长周期面波在厚沉积层中的形成以及传播特性，掌握厚沉积层对长周期地震动的放大效应，以期为该地区抗震设计地震动参数中长周期谱段的取值提供依据奠定基础。

有研究表明，厚沉积层是导致强烈长周期地震波形成并传播的主要原因，该强地震动可能会对具有较长自振周期的工程结构造成破坏。我们有必要研究华北地区厚沉积层对长周期地震动的影响。.我们改进了先前的辛格式离散奇异核褶积微分算子数值模拟地震波场的程序，用于模拟设定地震情形下华北地区区域厚沉积层地震动，分析厚沉积层对长周期面波地震动的影响程度。构建计算模型时，介质参数借助华北克拉通中东部地壳三维速度结构模型（HBCrust1.0）和公开的钻井资料；程序的震源模块可以考虑矩张量震源，及有限断层震源。有限断层震源模型的关键参数缺乏可靠的方法进行预测，只能基于假设，假设的合理性有待商榷。.我们借助1966年邢台地震的震源资料，完成了邢台地区设定地震长周期面波地震动模拟。在参数设定中，浅部沉积层的介质参数分层厚度要薄些，不能厚于250m，地震矩不能低于1.0e27dyne-cm，否则不会有长周期面波出现。我们得到了长周期面波的传播特性，长周期面波在震中距的一定范围内出现。震中距较小时面波还没有生成，震中距较大时面波又衰减消失。在震中距的一定范围内面波峰值会超过体波峰值。.我们的研究工作还在继续，试图呈现出和现有中国地震动参数区划图中给出的参数值能有可比性，明确获悉由于厚沉积层的存在，地震动参数区划图应该如何修正。争取能有个良好的结果，并形成一整套可行的方案，将我们的修正方法推广到华北地区。