二维起伏地形瑞利面波数值模拟研究

发布时间：2018-04-14 21:33

本文选题：瑞利面波 + 波场数值模拟　；参考：《西南交通大学》2017年硕士论文

【摘要】：瑞利面波广泛的被用于工程质量检测和工程勘察领域,得益于它的速度与横波速度相近且具有频散的运动学特性,除此之外瑞利面波还具有椭圆极化的动力学特性,它与速度频散具有一定的相似性,都会随着介质的变化而变化。瑞利面波在均匀半空间中速度频散和椭圆极化频散研究已经取得了一定成果,但起伏地形下瑞利面波的速度频散研究相对较少,相比之下椭圆极化频散则少之更少。本论文采用数值模拟的方法,针对起伏地形进行地震波场数值模拟,进而对速度频散和椭圆极化频散分析,本文主要从以下三个方面着手:1.以地震波传播理论为基础展开瑞利面波速度频散和椭圆极化频散的论述,对瑞利面波速度频散和椭圆极化率频散的提取方法进行了相关阐述。2.建立均匀半空间模型考察瑞利面波波场传播特征,验证理论分析结果的正确性与数值模拟方法的合理性,进而展开起伏地形条件下地震波的波场模拟,考察地形隆起高度和凹陷深度对瑞利面波速度频散和椭圆极化率频散的影响。3.建立存在局部异常体空洞的隆起和凹陷地形数值模型,分析该条件下地震波波场传播特征,与单纯地形数值模型作比较,深入研究局部异常体的存在对瑞利面波速度频散和椭圆极化率频散的影响。通过以上研究,取得了以下主要研究成果:1.与均匀半空间模型相比,单纯地形条件下数值模型的地震波波场较为复杂,不仅有震源激发时产生的体波和面波,还有地形效应产生的转波。由于地形效应的作用还会导致瑞利面波出现速度频散,具体表现为隆起地形的近源端区域瑞利面波速度降低而远源端区域速度增加,当为凹陷地形时则相反。并且这种变化趋势随着起伏程度的增加变得愈加明显。类似的地形效应还会导致瑞利面波出现椭圆极化率频散,具体表现如下:当为隆起地形时近源端区域瑞利面波椭圆极化率值变大而远源端区域变小,当为凹陷地形时则相反,并且随着地形起伏程度增加这种异常趋势变的愈加明显。2.对于存在局部异常体的地形模型而言,与单纯地形数值模型地震波波场具有一定的相似性,但也有区别,具体表现在地震波的传播不仅受到地形效应的影响还要受异常体的干扰,当地震波经过异常体时,异常体相当于一个震源会引起波场的转换,经对比研究发现,地形效应对瑞利面波速度频散和椭圆极化率频散的影响更为深刻,局部异常体只是在其周围区域加深了这种频散效应。通过本论文的研究深化了瑞利面波在起伏地形条件下波场传播的认识,强化了对瑞利面波速度频散与椭圆极化率频散的认知,完善了瑞利面波在起伏地形中探测方面的理论基础,对于完善学科理论,促进学科发展,具有极大的帮助。
[Abstract]:Rayleigh surface wave is widely used in engineering quality detection and engineering investigation, because its velocity is close to that of shear wave and has the characteristic of dispersion kinematics. In addition, Rayleigh surface wave also has the dynamic characteristics of elliptical polarization.It is similar to the velocity dispersion and will change with the change of the medium.Some achievements have been made in the study of Rayleigh surface wave velocity dispersion and elliptical polarization dispersion in uniform half-space, but the velocity dispersion of Rayleigh surface wave in undulating terrain is less than that of elliptical polarization dispersion.In this paper, the numerical simulation method is used to simulate the seismic wave field of the undulating terrain, and then the velocity dispersion and elliptical polarization dispersion are analyzed. In this paper, the following three aspects are discussed: 1.Based on seismic wave propagation theory, Rayleigh wave velocity dispersion and elliptical polarization dispersion are discussed, and the extraction methods of Rayleigh wave velocity dispersion and elliptical polarizability dispersion are expounded.A uniform half-space model is established to investigate the propagation characteristics of Rayleigh surface wave field. The correctness of the theoretical analysis results and the rationality of the numerical simulation method are verified, and the wave field simulation of seismic waves under undulating topography is carried out.The effects of height of terrain uplift and depth of depression on Rayleigh wave velocity dispersion and elliptical polarizability dispersion are investigated.The topographic numerical models of uplift and depression with local anomalous voids are established, and the propagation characteristics of seismic wave field under these conditions are analyzed and compared with the simple topographic numerical model.The influence of the existence of local anomalous bodies on Rayleigh wave velocity dispersion and elliptical polarizability dispersion is studied.Through the above research, we have obtained the following main research results: 1. 1.Compared with the homogeneous half-space model, the seismic wave field of the numerical model under the simple terrain condition is more complex, not only the body wave and the surface wave generated by the source excitation, but also the rotational wave generated by the topographic effect.Because of the effect of topographic effect, Rayleigh surface wave will appear velocity dispersion, which is represented by the decrease of Rayleigh wave velocity in near source region of uplift terrain and the increase of far source wave velocity, but the contrary when it is concave terrain.And the trend becomes more obvious as the degree of fluctuation increases.Similar topographic effects also lead to elliptical polarizability dispersion of Rayleigh surface waves, which is shown as follows: the elliptical polarizability of Rayleigh surface waves near the source end becomes larger while that of the distant source ends becomes smaller when the topography is uplift, and the opposite is true for the concave terrain.And with the increase of topographic fluctuation, this abnormal trend becomes more obvious. 2. 2.For the topographic model with local anomalous body, it is similar to the seismic wave field of the simple topographic numerical model, but it is also different from that of the simple topographic numerical model.The concrete manifestation is that the propagation of seismic wave is not only affected by topographic effect but also disturbed by abnormal body. When the seismic wave passes through the abnormal body, the anomalous body is equivalent to a source and will cause wave field conversion.The effect of topography on Rayleigh wave velocity dispersion and elliptical polarizability dispersion is more profound, and the local anomalous body only deepens the dispersion effect in the surrounding region.Through the research in this paper, we deepen the understanding of Rayleigh surface wave propagation in undulating terrain, and strengthen the understanding of Rayleigh wave velocity dispersion and elliptical polarizability dispersion.The theoretical basis of Rayleigh wave detection in undulating terrain is improved, which is of great help to the improvement of discipline theory and the development of subject.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU195

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