基于典型地质特征分析的大同盆地VS30预测研究

土体剪切波速是进行土层地震反应分析的动力学参数,对场地地震动参数确定具有重要意义。基于地质地貌分析,将大同盆地划分为5类典型地质单元。对盆地1429个钻孔剪切波速资料进行分析,探讨V_S30与V_S20的相关性,研究土体埋深、岩性、地质单元、标贯击数及密实度等地质特征对V_S的影响,并基于地质单元、剪切波速比、密实度系数及第四系上部覆盖层厚度相关性分析给出土体V_S30预测模型。研究结果表明,基于典型地质特征的V_S30预测模型拟合优度R2>0.90,预测精度很高,对于离散性较大、直接拟合估算较差及无剪切波速场地来说,以区分地质单元及土体类型的方式进行V_S30分解预测是良好的研究思路。首次在区分地质单元及土体类型的前提下提出剪切波速比及密实度系数,并将其与第四系上部覆盖层厚度综合应用于V_S30预测研究。研究结果可为大同盆地城市防震减灾规划、震害预测、区域性地震安全评价提供重要技术支撑。

Study on VS30 prediction of Datong Basin Based on the Analysis of Typical Geological Characteristics

The shear wave velocity of soil is a dynamic parameter for seismic response analysis of soil layer, which is of great significance to determine the ground motion parameters of the site. The shear wave velocity data of 1429 boreholes in the basin are analyzed, the correlation between V_S30 and V_S20 is discussed, and the influence of geological characteristics such as soil burial depth, lithology, geological unit, SPT blow number and compactness on V_S is studied. Based on the correlation analysis of geological unit, shear wave velocity ratio, compactness coefficient and thickness of Quaternary upper overburden, the soil V_S30 prediction model is given. The results show that the goodness of fitting of the V_S30 prediction model based on typical geological characteristics is greater than 0.90, and the prediction accuracy is very high. For the sites with large discreteness, poor direct fitting estimation and no shear wave velocity, it is a good research idea to distinguish geological units and soil types for V_S30 decomposition prediction. For the first time, the shear wave velocity ratio and compactness coefficient are proposed on the premise of distinguishing geological units and soil types, and they are integrated with the thickness of Quaternary upper overburden for V_S30 prediction. The research results can provide important technical support for urban earthquake prevention and mitigation planning, earthquake disaster prediction and regional earthquake safety evaluation in Datong Basin.