川滇地区基岩长周期地震动衰减关系研究

A complete review on the research of long-period ground motion is carried out. Accordingly, a new regression method is developed for the attenuation relationship of long-period acceleration response spectra on bedrock, which is based on the records of the digital accelerographs and GPS in different sites. Based on the analysis of the influence of the focal mechanism and the propagation path on the long-period ground motion, the principles of seismic reords are determined primarily. Then the records from the digital accelerographs and GPS within such principles in Sichuan-Yunnan region are collected. The baseline-correction is carried out on the digital strong motion records. The GPS data is selected from the continuous observation. The absolute displacement transformation is made. By analyzing the signal-to-noise ratio on the basis of the Fourier spectrum of the records, the credible frequency ranges are determined. The response spectra on the bedrock are compared with those on the free surfaces under different site conditions. The effects of the site conditions on the long-period ground motion are studied. And the relationship between the thickness of the soil layers and the influence period toplimits is built statistically, as well as between the equivalent shear wave velocity and the influence period toplimits. On this basis, the screening principles are determined by the credible frequency ranges of the records. The records from the digital accelerographs and GPS in Sichuan-Yunnan region are screened. The acceleration response spectra at the statistical periodic points are also calculated. The attenuation relationship of the acceleration response spectra on the bedrock site is establised. Based on the data of the acceleration response spectra obtained by screening and calculating, the regressing analysis is carried out. Additionally, the reliability of the attenuation relationship is examined by comparison.

深入分析国内外长周期地震动研究成果，提出基于各类场地上的数字强震动记录及GPS记录进行基岩长周期加速度反应谱衰减关系的统计回归新方法。通过震源机制和传播路径对长周期地震动的影响分析，确定地震记录的初选原则，收集川滇地区所捕获的满足初选条件的数字强震动记录及GPS记录；对数字强震动记录进行基线校正，对GPS连续观测数据进行截取和绝对位移转换；依据各记录傅里叶谱进行信噪比分析，确定其可信频带。通过基岩输入地震动反应谱和不同场地条件的分析模型自由地表反应谱对比分析，研究场地条件对长周期地震动的影响，统计建立土层厚度及等效剪切波速与影响周期上限的关系；结合各记录可信频带确定记录筛选原则，对所收集的川滇地区的数字加速度记录和GPS记录进行筛选，并计算其在统计周期点上的加速度反应谱。建立基岩加速度反应谱衰减关系，以筛选计算得到的加速度反应谱为基础数据，进行回归统计，通过对比检验所建立衰减关系的可靠性。

概括介绍了长周期地震动衰减关系研究现状及其相关研究成果，指出了现有相关研究中存在的问题，并阐明了开展长周期地震动衰减特性研究的必要性。介绍并应用了基于地震动加速度基线校正方法，峰值加速度、加速度反应谱、累积绝对速度计算方法，以及最小二乘法的两步回归分析方法。介绍了合成人造地震动的方法、一维土层地震反应分析的等效线性化方法及不同场地条件下的6个实际工程场地分析模型，并进行了人造地震动时程的合成和土层水平向地震反应的计算，对比分析了基岩场地和不同土层场地自由地表加速度反应谱，讨论了场地覆盖层厚度对长周期地震动的影响，并通过对比分析汶川地震主震强震动记录反应谱进一步验证了数值模拟结果所得结论。通过典型场地的数值模拟及实际地震记录分析，讨论了将土层场地上的强震动记录直接应用于基岩场地上的长周期地震动加速度反应谱衰减关系回归统计分析的适用条件。以满足筛选条件的强震动加速度记录为基础数据，基于最小二乘法的两步回归分析，建立了基岩场地上8-20s内6个周期点的加速度反应谱衰减关系，并通过随震级、距离的变化分析，及与实际地震记录的对比，讨论了衰减关系回归统计结果的合理性。