圆弧状沉积盆地与软土单覆盖层出平面地表运动对比
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摘要
采用解析方法 ,通过圆弧状沉积盆地与同样参数的软土均匀单覆盖层的对比 ,研究沉积盆地对平面SH波二维散射效应和其出平面地表运动。数值对比结果表明 :(1)波垂直入射时盆地中央地表位移幅值反应 ,其随频率变化形式与软土单覆盖层的地表运动有较强的对应性 ,且此时单覆盖层地表位移幅值为其下限 ;(2 )盆地的二维散射效应特点显著波的汇聚作用使盆地中的地表运动显著放大 ,总体上较软土单覆盖层的地表位移幅值要大 ,其频域内的最大反应则明显大于单覆盖层情况 ,但最大反应在盆地表面出现的位置依赖于入射波角度、盆地深宽比和盆地的软硬程度 ;(3)沉积盆地中地表位移运动有强烈扭转效应 ,且随盆地变软和入射波频率增高而增强
The two dimensional scattering effects of the plane SH waves by an alluvial valley are presented through the comparison of the out of plane surface ground motion between a circular arc alluvial valley and a single overburden soft layer using the analytical method. The numerical results of the comparison indicate: (1) When the vertical waves are excited, the surface displacement amplitudes in the middle of the alluvial valley show the similar character to that on the single overburden layer and in this case, the surface displacement amplitudes of the single overburden layer are the lower limits of those of the alluvial valley; (2) Because of the wave concentration effects of the alluvial valley the surface motion on the alluvial valley is obviously amplified and the maximum amplification of the surface motion is significantly larger than that on the surface of the single overburden layer, but the location of the maximum amplification of the surface displacement amplitudes on the alluvial valley mainly depends on the angle of the incident waves and the depth to width ratio and rigidity of the alluvial valley; (3) The notable torsion effects of the surface ground motion on the alluvial valley are illustrated and the torsion effects become stronger as the alluvial valley is softer and the frequency of the incidence is higher.
The two dimensional scattering effects of the plane SH waves by an alluvial valley are presented through the comparison of the out of plane surface ground motion between a circular arc alluvial valley and a single overburden soft layer using the analytical method. The numerical results of the comparison indicate: (1) When the vertical waves are excited, the surface displacement amplitudes in the middle of the alluvial valley show the similar character to that on the single overburden layer and in this case, the surface displacement amplitudes of the single overburden layer are the lower limits of those of the alluvial valley; (2) Because of the wave concentration effects of the alluvial valley the surface motion on the alluvial valley is obviously amplified and the maximum amplification of the surface motion is significantly larger than that on the surface of the single overburden layer, but the location of the maximum amplification of the surface displacement amplitudes on the alluvial valley mainly depends on the angle of the incident waves and the depth to width ratio and rigidity of the alluvial valley; (3) The notable torsion effects of the surface ground motion on the alluvial valley are illustrated and the torsion effects become stronger as the alluvial valley is softer and the frequency of the incidence is higher.
引文
[1] 中国赴日地震考察团.日本阪神大地震考察[M ].北京:地震出版社,1995.
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[2] 廖振鹏.工程波动理论导引[M].北京:科学出版社,1996.
[3] 李小军.非线性场地地震反应分析方法的研究[D].哈尔滨:中国地震局工程力学研究所博士学位论文,1993.
[4] 丁海平.线性土-结构动力相互作用分析方法的改进[D].哈尔滨:中国地震局工程力学研究所博士学位论文,2000.
[5] SingnSK ,MenaE ,CastroR .Someaspectsofsourcecharacteristicsof19September1985Michaoacanearthquakeandgroundmotionamplifi cationinMexicoCityfromstronggroundmotiondata[J].BullSeismSocAmer,1988,78:451-477.
[6] TrifunacMD .Surfacemotionofasemi-cylindricalalluvialvalleyforincidentplaneSHwaves[J].BullSeismSocAmer,1971,61:1155-1770.
[7] WongHL ,TrifunacMD .Surfacemotionofasemi-ellipticalalluvialvalleyforincidentplaneSHwaves[J].BullSeismSocAmer,1974,64:1389-1408.
[8] YuanXM ,LiaoZP .ScatteringofplaneSHwavesbyacylindricalalluvialvalleyofcircular-arccross-section[J].EarthqEngngStructDy namics,1995,24:1303-1313.
[9] 韦晓.土层反应分析中输入界面的选取[D].哈尔滨:中国地震局工程力学研究所硕士学位论文,1993.
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