地震波斜入射下深厚覆盖层河谷加速度分布特征分析

Characteristic analysis of acceleration of deep overburden canyon topography under obliquely incident seismic waves

我国西部地区普遍具有高山峡谷和深厚河床覆盖层的特点,而对于深厚覆盖层河谷场地的地震动分布特征的研究却很少。本文采用黏弹性人工边界及其相关地震动等效荷载输入的方法,研究了地震动P波和SV波入射角度及入射波峰值对深厚覆盖层河谷场地加速度放大系数分布特征的影响。结果表明:(1)P波和SV波入射角度一定时,入射波峰值对河谷两岸平台及岸坡的加速度放大系数影响很小;(2)P波左侧入射时,随着入射角度的增大,左岸平台及岸坡x分量的加速度放大系数增幅较大,z分量的加速度放大系数增幅较小保持在2倍左右,河谷覆盖层表面x和z分量加速度放大系数逐渐趋于均匀分布;(3)SV波左侧入射时,随着入射角度增大,整个河谷覆盖层表面x分量的加速度放大系数呈现出坡脚附近较小,中间部位和两岸平台较大;z分量放大系数呈现出相反的规律。这些结论可以为具有覆盖层河谷工程场址的地震动参数设计及加速度监测点布置提供一定的参考。

In western China,there are generally high mountain canyons and deep riverbed overburden.However,there are few studies on ground motion distribution in canyon with deep overburden.Using viscous-elastic artificial boundary and equivalent ground motion input method,the effects of the incidence angles of ground motion P wave and SV wave and their peaks on the distribution characteristics of acceleration amplification coefficients in the deep overburden canyon topography are studied in this paper.The results show that:(1)When the incidence angle of P wave and SV wave is constant,the peak of incident wave has little effect on the acceleration amplification coefficient of the platform and bank slope of the canyon;(2)When the P wave is incident on the left side,with the increase of incidence angle,the acceleration amplification coefficient of x component of the left bank platform and bank slope increases greatly,while the acceleration amplification coefficient of z component of the left bank platform and bank slope increases slightly,maintaining about 2 times.The acceleration amplification coefficient of x and z components of the canyon overburden surface gradually tends to be evenly distributed.(3)When the SV wave is incident on the left side,with the increase of the incidence angle,the x component acceleration amplification coefficient of the canyon overburden surface is smaller near the foot of the slope,larger in the middle part and the platform on both sides.The z component amplification coefficient shows the opposite law.These conclusions can provide some references for the design of ground motion parameters and the layout of acceleration monitoring points of deep overburden canyon engineering sites.