瑞利面波高阶模式椭圆极化频散特征理论推导及数值模拟研究

Theory and numerical simulation study of the higher modes elliptical polarization dispersion characteristics of Rayleigh surface waves

随着城市地下空间的深入开挖和利用,地表变形和沉降塌陷等最常见的工程事故等问题给人民和国家造成了严重生命财产损失.为降低和避免这一危害,迫切需要一种能够在事故发生前对其进行有效观测和预警的方法.传统大地测量、GPS等方法只能在位移发生后进行测量,抗压抗剪等地质试验手段可通过观测介质物性参数对其状态进行预测,但其效率低成本高.常规物探手段如电法、GPR、主动源或被动源地震等方法,因本身方法原理或周围环境所限,不能满足城市环境下的有效测量和预警.传统瑞利面波速度频散法野外工作需布置长大排列,因此也受限于城市环境.为解决上述问题,作者通过前期研究提出了基阶瑞利面波椭圆极化频散方法,即单点矢量瑞利面波法,该方法无需长大排列,只需通过单点采集的多分量信息对地下介质结构进行推断,因此可有效解决上述应用瓶颈问题.本文在前期研究基础之上,进一步对多模式瑞利面波椭圆极化特征进行了理论和数值模拟研究,结果表明,类似基阶面波,高阶同样具有椭圆极化频散特性,且其与地层(速度)泊松比结构同样密切相关,甚至特征更明显;但由于具有较强特征椭圆极化特性的某一面波模式,其能量可能较弱,误差也可能较大.因此,在利用瑞利面波椭圆极化特征时,应综合考虑不同模式面波能量和椭圆极化特征的相对强弱,从而为利用单点多模式矢量瑞利面波法评价或探测、监测预警地层泊松比结构或其变化等,提供坚实的理论基础和可行性研究依据.

Conventional geophysical exploration methods,such as electric method,GPR,active source or passive source earthquake methods,cannot meet the effective measurement and early warning in the urban environment due to the limited method principle or the surrounding environment.Traditional velocity dispersion Rayleigh wave method needs arranging long array in field work,so it is also limited by the urban environment.In order to solve the above problems,the author put forward the fundamental Rayleigh wave elliptic polarization dispersion method,that is also the Single Point Vector Rayleigh wave method(SPVR).This method does not need long arrangement,it can infer the underground medium structure through the multi-component information collected by a single point,so it can effectively solve the above application bottleneck problem.On the basis of the previous study,this paper further studied the theoretical and numerical simulation characteristics of the multi-modes Rayleigh wave,and the results show that,similar to fundamental elliptic polarization,the higher orders are also closely related to the formation(velocity)Poisson ratio structure,which are even more stronger.However,one mode Rayleigh wave with strong elliptic polarization may not be strong in energy,and that may cause large error.Therefore,when using the characteristics of one mode Rayleigh wave elliptic polarization,it should be considered the relative strength of the energy and the elliptic polarization characteristics,so as to provide a solid theoretical basis and feasibility study for using the Single Point Multi-modes Vector Rayleigh wave method((SPMVR).)to evaluate or detect,monitor and early warning formation Poisson ratio structure or its change.