高频面波中不同模态的特性及应用

发布时间：2018-01-12 16:03

本文关键词：高频面波中不同模态的特性及应用　出处：《中国地质大学》2016年博士论文　论文类型：学位论文

【摘要】：获取横波速度结构是面波研究工作的重点,也是地球物理野外实践工作的目的。通过钻井方法,可以获得浅地表的横波速度剖面。然而,这通常需要大量的钻孔资料,花费大量的人力、物力和财力,并且对环境和生态造成不可逆的影响。高频面波方法为获得拟二维横波速度剖面提供了新的思路。它具有非侵入性、非破坏性、高效且成本低的特点,使其作为地震勘探方法的一个分支得以创立并日益发展,以解决浅层工程地质和环境问题。高频面波方法主要利用面波在层状介质中的频散特性进行浅地表勘探,主要包括了瑞雷波方法和勒夫波方法。在均匀半空间条件下,瑞雷波没有频散现象,而是以一个固定的相速度(例如,当泊松比为0.25时,相速度为横波速度的0.92倍)传播。然而,当地下介质为多层介质时,瑞雷波出现频散现象。对于给定的模式,长波长的成分具有更深的穿透深度,并且对深部更加敏感；短波长的成分则对表层介质更加敏感。高频面波在层状介质中会发育多阶模态,按照顺序依次被命名为基阶、一阶高阶、二阶高阶等。因此,面波方法可以通过反演单模态或者联合反演多模态面波的相速度来获得地表介质的横波速度。因此,判定面波模式阶数,拾取准确可靠的面波相速度值对反演结果的可靠性至关重要。“模式误判’’现象是高频面波方法的模式识别过程中经常遇到的问题。本论文研究了面波不同模态的特征,提出了：(1)在高泊松比情况下,采集到的瑞雷波地震记录含有非几何波,它是一类泄露波。它的存在会导致拾取频散相速度时,将泄露波能量当作面波基阶或者高阶的能量,从而使得反演结果数值相对真实速度模型结果偏大；(2)“模式接吻”现象会导致的模式误判。“模式接吻”现象是瑞雷波勘探过程中经常会出现的问题,它会影响对基阶相速度的拾取,使得反演结果比真实模型的横波速度偏大。数值分析证明了当模型中存在强横波速度分界面时,会增加“模式接吻”现象出现的可能性。(3)在野外数据采集过程中的不当操作或者不合理的偏移距,有可能会造成数据的缺失,产生削平波,它也会影响频散能量图中相速度的拾取。数值模拟实验或(和)实例建议：在采集瑞雷波数据时,选择合适的炮检距和设置合适的仪器动态范围是十分重要的；在提取频散能量之前,对炮集记录进行切除或者滤波等预处理操作可以获得更高精度的频散能量图。此外,瑞雷波勘探的最终目的是为了获取地下的横波速度剖面。在野外勘探过程中,经常采用滚动排列的方式进行多炮的数据采集,这增加了野外的工作任务。本论文提出了一种新的瑞雷波勘探方法-虚源面波多道分析方法,它通过互相关计算,可以实现将检波器位置当作虚源位置,产生虚源炮集记录代替野外放多炮记录,减少野外工作量。由于瑞雷波多模态的特性,模式分离和重构对获得准确的经验格林函数至关重要。数值模拟结果和野外实例证明了该方法相对传统的滚动排列的面波多道分析方法,可以增加工作效率,在浅地表勘探中具有可行性。
[Abstract]:To obtain the S-wave velocity structure of surface wave is the focus of research work, and geophysical field practice work. Through the drilling method, can obtain the shallow shear wave velocity profile. However, it usually requires a large number of borehole data, spend a lot of manpower, material and financial resources, and causing irreversible effects on the environment and ecology high frequency surface wave method provides a new way to get quasi two dimensional shear wave velocity profile. It is non-invasive, non-destructive, high efficiency and low cost, which is a branch of seismic exploration method is created and developed increasingly, in order to solve the shallow engineering geological and environmental problems. The dispersion characteristics high frequency surface wave methods using surface waves in layered medium shallow surface exploration, including the Swiss Leibo method and Loew wave method. In the homogeneous half space under the condition of no Rui Leibo dispersion phenomenon, and With a fixed speed (0.92 times for example, when the Poisson ratio is 0.25, the phase velocity for the shear wave velocity of propagation). However, when the underground medium for multiple media, Leibo Rui dispersion. For a given mode of long wavelength components with the penetration depth is deeper, and more sensitive deep; short wavelength components are more sensitive to the surface layer. In the layered media will be the development of multi modal high-frequency surface wave, in accordance with the order is named for the base order, one order higher order, two order higher order. Therefore, the surface wave phase velocity inversion method can through single mode or multi joint inversion the mode of surface wave to obtain surface S-wave velocity media. Therefore, to determine the surface wave mode order, pick accurate and reliable surface wave phase velocity on the inversion results reliability is essential. "" "phenomenon is the high frequency mode error of the surface wave method in pattern recognition Frequently encountered problems. This paper studies the characteristics of surface wave, different modes are proposed: (1) than in the case of high Poisson, Rui Leibo earthquake records collected with non geometric wave, it is a kind of relief. It will lead to our pickup dispersion phase velocity, wave will leak can the amount of order or higher order bases as surface energy, which makes the inversion results of numerical results is too large relative to the actual velocity model; (2) "mode of misjudgment phenomenon will result in the mode of kissing". "Kiss mode" phenomenon is often appear in Leibo Rui in the process of exploration, it will affect the pickup based on order phase the speed of the inversion result is bigger than the shear wave velocity of the real model. The numerical analysis shows that when there are strong shear wave velocity interface model, will increase the possibility of "pattern kissing" phenomenon. (3) in the field of data acquisition in the process of operation or not when Offset unreasonable distance may cause data missing, have cut flat wave, it will also affect the pick-up phase velocity dispersion energy diagram. Numerical simulation experiments or (and) examples suggested: in the acquisition of Leibo Rui data, select the appropriate offset and set the appropriate dynamic range of instrument it is very important; before the bulk energy in the frequency of data extraction, removal or filtering operation can obtain higher accuracy of dispersion energy. In addition, the ultimate goal is to obtain the Swiss Leibo exploration of the underground S-wave velocity profile. In the exploration process, often using the rolling arrangement the way of data acquisition of multi gun, which increases the field task. This paper proposes a new method - Rui Leibo source surface wave exploration Virtual Multi-channel analysis method, it can be achieved by calculating the cross-correlation, the detector position as The virtual source position, generating virtual source data set to replace the outdoor shot records, reduce the workload of the field. Because of the characteristics of Leibo Rui multimodal, empirical Green function mode is crucial to obtain accurate separation and reconstruction. The results of numerical simulation and field examples prove that this method compared with the traditional rolling surface wave multi arrangement analysis method. Can increase the work efficiency, it is feasible in the shallow exploration.

【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P631.4

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