【作者】 潘冬明；

【导师】 崔若飞；

【作者基本信息】 中国矿业大学 ， 地球探测与信息技术， 2009， 博士

【摘要】 早在1885年,英国数学物理学家Rayleigh在求解沿自由表面传播的波动方程时,从理论证明了存在一种弹性波,它沿自由表面传播,质点运动轨迹为逆椭圆,振幅随深度指数衰减,后来被称之为瑞雷波(或R波)。此后广泛地利用天然地震记录的瑞雷波来研究地球内部的结构,工程上用面波谱分析法(SASW)来研究表土层结构。为克服面波谱分析法提取频散曲线抗干扰能力差、不能得到高阶模式频散曲线等缺点,提出了多道面波分析法(MASW)。该方法对多道记录进行波场分析提取瑞雷波频散曲线。在实际勘探过程中,基阶瑞雷波数据容易被体波及高阶模式瑞雷波干扰。本文对瑞雷面波的传播规律及其频散特性进行了研究,采用改进的传播矩阵法进行了典型地层的瑞雷面波频散曲线计算。对常用的面波频散分析方法进行了详细研究,并对τ?p变换法、拉东变换(LRT)法进行了改进。研究了基于频散曲线的面波合成方法,并采用反射率法对全波场地震记录进行了合成和频散分析。全面分析了采集参数对瑞雷波频散分析的影响。研究表明:排列方式、震源类型和深度、场地的激发条件、检波器的类型对瑞雷波的频率成份都有着重要影响。其中震源的能量对能否激发出足够低频的瑞雷波信号能量起着决定性的作用。本文所研究的频散分析方法,不对原始记录进行数字处理(时域滤波、FK滤波等),避免了数字处理效应的影响(如吉普斯效应等)。而是通过对信号的频谱分析、结合场地的地质条件,选择频散分析的频率、速度范围,来达到规避高视速度的直达波、反射波。通过对不同场地条件、不同震源激发及不同类型检波器等采集的瑞雷波记录进行频散分析,进一步验证了所研究的频散分析方法的有效性及程序的适应性,取得了较好的效果。煤田反射地震勘探的接收排列长度、偏移距分布范围、检波器与地震仪的性能以及时间采样率和记录长度都不妨碍面波波场的接收,虽然采用深孔激发、高频检波器等措施来压制瑞雷波,但煤田反射波勘探中较少采用检波器组合,实际资料中瑞雷波的能量仍然较强,这为利用反射波资料进行瑞雷波勘探创造了有利条件。从频散分析的结果来看,可以在煤田反射波勘探资料上进行瑞雷波分析,以提取极其重要的表层横波速分布,为转换波静校正等提供可靠资料。更多还原

【Abstract】 As long ago as 1885, the English mathematician and physicist Lord Rayleigh theoretically proved that there was a kind of elastic waves which propagate along the free surface with an anti-clockwise elliptic particle trajectory and its amplitude with an exponential decay with depth. The wave was named as Rayleigh wave or R-wave later. Subsequently, Rayleigh waves have been widely applied to studying Earth’s internal structure by seismologists from the analysis of earthquake records, and near surface soil structures through the use of Spectral Analysis of Surface Waves (SASW) by engineers. To overcome the weakness of SASW method, such as, low precision of dispersion curves,multimode data mixture,body wave energy contamination and the difficulty to calculate the high-mode dispersion curves, the Multi-channel Analysis of Surface Waves (MASW) has been proposed. Velocity dispersion curves are extracted from multiple trace records by wave field analysis. The fundamental mode of Rayleigh waves,however, are easily contaminated by the high-modes or body wave energy in the real data.By studying the characteristics of the Rayleigh-wave propagation and dispersion, in this paper the modified propagation matrix method was adopted to calculate the dispersion curves of Rayleigh-wave disperse in multi-layered media. Common Rayleigh-wave velocity dispersion curves are extracted through the use ofτ?p transform or Radon transform. Additionally, the author has studied the Rayleigh-wave synthetic method based on velocity dispersion curve and adopted reflectivity method to analyze synthetic records and velocity dispersion of whole seismic wave wavefield. I have also analyzed comprehensively the influence of acquisition parameters on Rayleigh-wave velocity dispersion. The results have showed that array characteristics, source pattern and target depth, site condition, and type of the geophone play an important role on the Rayleigh-wave frequency composition. Among these, the source energy played a dominant role in exciting the low frequency Rayleigh-wave signals.The computation of velocity dispersion method in this paper does not use any digital process such as 1-D filtering, f-k filtering, and it avoids the impacts of digital processing just like Gipps effect. However it discriminates the direct waves and reflected waves using the frequency analysis and the geological condition of the sites to choose frequency and velocity range. It is further verified that the velocity dispersion method is valid and credible through the analysis of different sites, sources, and different pattern of geophones. So it gives rise to better results.Receiver array length, offset distribution range, performance of geophone and seismograph, time sampling rate and length of the record have no effects on Rayleigh-waves in coal exploration. Although some measures has been taken to avoid the Rayleigh-waves such as using the deep hole to excite and the high-frequency geophone to receive, the energy of the Rayleigh-waves still appears because geophone grouping is rarely applied in coal exploration. It provides advantage to carry out Rayleigh-wave exploration in reflected waves. From the velocity dispersion analysis results, extracting the S-wave velocity distribution of near-surface using the Rayleigh-wave analysis from reflected waves can provide reliable data for converted wave statics.更多还原