高频背景噪声波场模拟与面波成像

发布时间：2019-04-26 06:16

【摘要】：本论文使用背景噪声波场模拟方法进行背景噪声面波成像方面的研究。背景噪声方法已被逐渐应用在浅地表等领域,因为人们可以使用该方法获得地下横波速度模型。地下横波速度是地质勘测和地质灾害评估中的重要参数。同时由于背景噪声中面波的频率可低于5Hz,所以人们通过该方法可以获得地下较深(100m)的速度信息。人们主要使用背景噪声中的面波,因为面波能量较强。因此对于背景噪声面波成像的研究可以推进人们对于该方法的应用。该方法在实际使用中,人们发现了其中存在的问题(如实际中噪声源分布不均匀与理论假设不同),这些问题将影响该方法获得结果的正确性。所以有必要对于背景噪声面波成像进行研究。波场模拟是地震学研究中的重要方法之一,可以被用来模拟噪声数据。因此本论文将背景噪声波场模拟应用于面波成像的研究中,关注背景噪声剪切分量中的瑞雷波和噪声源不均匀分布(本论文中剪切方向定义为垂直于通过所有检波器的大圆路径或者小尺度上的测线的方向。)。人们目前使用地震干涉方法从背景噪声剪切分量获得勒夫波,并忽略了剪切分量中的其它成分。但实际上当噪声源偏离测线分布时,剪切分量含有瑞雷波。本论文通过理论推导、对模拟数据与实际数据的处理,证明瑞雷波存在于剪切分量的地震干涉结果中。通过理论推导获得了剪切分量互相关中瑞雷波的表达式；通过背景噪声模拟获得只含有瑞雷波的剪切分量数据,对模拟数据处理结果中显示出瑞雷波；对于在新疆采集的实际剪切分量数据处理后,频率-速度域显示出瑞雷波的能量。接着本论文讨论了该瑞雷波的影响。由于在频率大于0.1Hz的部分,瑞雷波和勒夫波相速度接近,所以如果在拾取勒夫波频散曲线时忽略瑞雷波,获得的勒夫波相速度将会偏离真实值,反演结果也将不能反映真实的地下速度结构。对于这个可能的误判,在使用背景噪声地震干涉方法解决浅地表地质问题时,本论文推荐使用面波多道分析方法。背景噪声地震干涉理论假设噪声源均匀分布,但该假设在实际中往往难以满足,噪声源不均匀分布将会导致获得的经验格林函数和面波相速度偏离真实值。本论文讨论了噪声源不均匀分布对于被动源方法(背景噪声地震干涉方法、空间自相关、微动折射方法和被动源面波多道分析方法)的影响,将这些方法计算的面波相速度与理论面波相速度进行了对比。讨论中使用了噪声源分布不均匀情况下的背景噪声模拟数据。结果显示,在背景噪声观测中,如果噪声源在偏离测线方向分布,使用上述被动源方法计算的面波相速度都将偏离理论值,无法获得接近真实的横波速度模型；如果布置测线使得主要噪声源沿测线方向分布,人们对于这样的噪声数据可以使用地震干涉方法、微动折射方法和被动源面波多道分析方法计算获得较为准确的面波相速度。
[Abstract]:In this paper, the background noise wave field simulation method is used to study the background noise wave imaging. The background noise method has been gradually applied in the shallow surface area, because people can use the method to obtain the underground shear wave velocity model. The underground shear wave velocity is an important parameter in the geological survey and geological hazard assessment. At the same time, because the frequency of the surface wave in the background noise can be lower than 5 Hz, the speed information of the underground depth (100 m) can be obtained by the method. The surface wave in the background noise is mainly used because the surface wave energy is strong. Therefore, the research on the background noise wave imaging can promote the application of the method. In practical use, the method has found problems in the method, such as the fact that the distribution of the noise source is not uniform and the theoretical assumption is different, and the problems will affect the correctness of the results obtained by the method. Therefore, it is necessary to study the background noise wave imaging. The wave field simulation is one of the important methods in the study of seismology and can be used to simulate the noise data. In this paper, the background noise wave field simulation is applied to the research of surface wave imaging, and it is concerned that the Rayleigh wave and the noise source in the background noise shear component are not uniformly distributed (the shearing direction in this paper is defined as the direction perpendicular to the large circle path through all the detectors or the measuring line on the small scale). . People are currently using the seismic interference method to obtain the lvwave from the background noise shear component and ignore the other components in the shear component. But in practice, the shear component contains the rayleigh wave as the noise source deviates from the line distribution. In this paper, it is proved that the Rayleigh wave is present in the result of the seismic interference of the shear component by the theoretical deduction and the processing of the simulation data and the actual data. the expression of the Rayleigh wave in the cross-correlation of the shear components is obtained through the theoretical derivation; the shear component data containing only the Rayleigh wave is obtained through the background noise simulation, and the Rayleigh wave is displayed in the simulation data processing result; and after the data processing of the actual shear component acquired in Xinjiang, The frequency-velocity field shows the energy of the Rayleigh wave. The influence of the Rayleigh wave is then discussed in this paper. Since the Rayleigh wave and the lvwave phase are close to each other at a frequency greater than 0.1 Hz, if the Rayleigh wave is ignored in the pick-up wave dispersion curve, the obtained lvwave phase velocity will deviate from the true value, and the inversion result will not reflect the real underground velocity structure. For this possible misjudgment, when using the background noise seismic interference method to solve the shallow surface geological problem, the paper recommends using the surface wave multi-channel analysis method. The background noise seismic interference theory assumes that the noise source is uniformly distributed, but the hypothesis is often difficult to meet in practice, and the non-uniform distribution of the noise source will result in the obtained empirical Green function and the surface wave phase velocity deviate from the true value. In this paper, the influence of the non-uniform distribution of noise sources on the passive source method (background noise seismic interference method, space self-correlation, micro-refraction method and passive source surface channel analysis method) is discussed, and the surface wave phase velocity calculated by these methods is compared with the theoretical surface wave velocity. Background noise simulation data in the case of non-uniform noise source distribution is used in the discussion. The results show that, in the background noise observation, if the noise source is distributed in the deviation line direction, the surface wave phase velocity calculated by using the passive source method will deviate from the theoretical value, and the near real shear wave velocity model cannot be obtained; If the survey line is arranged so that the main noise source is distributed along the line direction, one can use the seismic interference method, the micro-refraction method and the passive source-plane channel analysis method to calculate the surface wave phase velocity.
【学位授予单位】：中国地质大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P631.4

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