安宁河河谷及邛海地区土层场地对地震动的放大作用

场地土层对地震动的影响研究一直是地震工程研究的主要问题之一。利用汶川地震中安宁河及邛海周边地区6个台站记录到的主震的加速度时程,采用传统谱比法研究了5个土层台站所在场地对地震动的放大作用,研究结果表明:1该区场地对地震动的放大作用与工程地质分区有着很好的相关性,不同的工程地质分区对地震动的放大效应不同,按放大作用大小排序,邛海湖滨平原亚区(Ⅲ3)邛海洪泛平原亚区(Ⅲ_2)安宁河平原区(Ⅱ)山麓坡洪积亚区(Ⅰ_2)中山基岩亚区(Ⅰ_1)。2工程地质分区为山麓坡洪积亚区(Ⅰ_2)的场地对地震动低频分量没有放大作用,但是对地震动高频成分放大作用显著。3工程地质分区为安宁河平原区(Ⅱ)的场地对地震动低频和高频都有放大效应,并且高频放大作用大于低频,并且3个分量放大作用在低频和高频表现不同,低频时地震动放大效应UDNSEW,高频时地震动放大效应EWNSUD。4工程地质分区为邛海洪泛平原亚区(Ⅲ_2)的场地对地震动低频和高频放大作用都非常显著,并且放大系数最大值所在的频带都在1 Hz左右,且放大最大值相差不大。5对于工程地质分区为邛海湖滨平原亚区(Ⅲ_3)的场地对地震动低频和高频放大作用都有放大效应,放大系数较大,且放大效应显著频段分布较宽。

Amplification effect of soil sites on ground motion in Anning River valley and Qionghai Lake area

Thet effect of site soil on ground motion is one of the main issues about earthquake engineering research. Based on the acceleration time histories recorded at 6 stations in Anning River and Qionghai Lake area, the amplification effect of 5 soil stations is studied by using the traditional spectral ratio method. The results are as follows: (1) There is good correlation between the amplification on ground motion in these sites and the geological zone, and the amplification effect on ground motion is different in different geological zones. According to the amplification of the size, the descending sequence is Qionghai Lake Plain subregion (Ⅲ₃), Qionghai Lake and flood plain subregion (Ⅲ₂), Anning River Plain area (Ⅱ), piedmont alluvial subregion (Ⅰ₂) and Zhongshan bedrock subregion (Ⅰ₁). (2) The piedmont alluvial subregion has no amplification effect on the low-frequency component of ground motion but significant amplification effect on the high-frequency one. (3) The Anning River Plain area has amplification effect on both the low-and high-frequency components of ground motion, and the amplification effect on the high frequency is stronger than that on the low frequency. The amplification effects of three components are different, that is, the descending amplification in the low frequency is UD, NS and EW, and that in the high frequency is EW, NS and UD. (4) The Qionghai Lake flood plain subregion has significant amplification effect on both the low-and high-frequency components of ground motion, and the maximum factor of amplification is about 1 Hz, with small differences among the maximum factors. (5) The Qionghai Lake Plain subregion has amplification effect on both the low-and high-frequency components of ground motion, the amplification factor is large, and the distribution band of significant amplification is wide.