Improving SASW Dispersion Measurements with Source Correlation and Receiver Arrays

摘要9901225 PI：James A.Bay研究所：犹他州州立大学“利用震源相关和接收器阵列改进声表面波频散测量”面波频谱分析方法是一种确定浅层土壤和岩石沉积物工程性质的地震技术。它涉及在地面上产生地震波，并通过在地面上安装一些接收器来监测这些波的运动。在SASW测试中经常遇到的一个困难是，来自其他来源的地震能量也由接收器测量，例如交通、工业设施，甚至树木中的风。这种不需要的地震能量或噪声会污染SASW测量，并可能导致错误的结果。这项拟议的研究旨在研究两种方法来最小化噪声对声表面波测量的影响。这些方法应该会提高SASW测量的质量。第一种方法是利用信源相关性。这包括测量SASW源施加到地面的力，并将该强迫函数与在每个接收器处测量的信号相关联。通过重复测量和对相关函数求平均，将降低声表面波测量中的噪声水平。使用源相关性的另一个好处是SASW测试，它将允许对实验结果的质量进行统计确定。使用这种方法的另一个好处是，利用源相关性，在激励函数和每个接收器之间计算的相干函数将准确地量化每个接收器处的噪声的频谱分布。利用该信息，可以统计地确定相干性级别、平均数和测量相位的置信度区间之间的关系。利用该关系，执行SASW测试的操作员将能够基于相干级别来确定需要多少平均值才能达到期望的测量精度。第二种方法是减少噪声的影响，使用接收器阵列将噪声对面波频散测量的影响降至最低。接收器阵列是串联连接的接收器数量的几何分布，以便将来自所有传感器的信号相加。几十年来，勘探地球物理学家一直使用接收器阵列来最大限度地减少深反射测量中表面波(地球物理学家称之为地滚)的影响。通过使用传感器的不同空间分布，可以设计接收器阵列，以选择性地测量表面波并消除来自震源位置以外的点的噪声。这项研究将导致更高质量的SASW现场测量。此外，准确量化声表面波测量中的噪声水平将为未来评估声表面波最终结果分辨率的研究提供有价值的工具。

Abstract 9901225 PI: James A. Bay Institution: Utah State University "Improving SASW Dispersion Measurements with Source Correlation and Receiver Arrays" The Spectral-Analysis-of Surface-Waves (SASW) method is a seismic technique for determining engineering properties of shallow soil and rock deposits. It involves generating seismic waves at the ground surface and monitoring the motions of those waves with a number of receivers positioned on the ground surface. One difficulty that is often encountered in SASW testing is that seismic energy from other sources, such as traffic, industrial facilities and even wind in trees is also measured by the receivers. This unwanted seismic energy, or noise, contaminates SASW measurements and can lead to erroneous results. This proposed research is to investigate two approaches to minimize the influence of noise on SASW measurements. These methods should improve the quality of SASW measurements. The first proposed approach is to use source correlation. This involves measuring the force applied to the ground by the SASW source, and correlating that forcing function with the signal measured at each receiver. By repeating the measurement and averaging the correlated functions, the noise level in the SASW measurement will be decreased. An additional benefit of using source correlation is SASW testing is that it will allow a statistical determination of the quality of experimental results. An added benefit to using this approach is that with source correlation, coherence functions calculated between the excitation function and each receiver will accurately quantify the spectral distribution of noise at each receiver. With this information, the relationship between coherence level, number of averages, and the confidence interval of the measured phase can be determined statistically. With this relationship an operator performing SASW testing will be able to determine how many averages will be required to achieve a desired measurement accuracy based upon the coherence level. The second approach is to reducing the influence of noise the use of receiver arrays to minimize the effects of noise on surface wave dispersion measurements. A receiver array is a geometric distribution of number of receivers connected in series, so that signals from all the sensors are summed. For decades, exploration geophysicists have used receiver arrays to minimize the effects of surface waves (which geophysicists refer to as ground roll) in deep reflection surveys. By using different spatial distributions of the sensors, receiver arrays can be designed that will selectively measure the surface waves and eliminate noise emanating from points other than the source location. This research will result in higher quality SASW field measurements. In addition, accurately quantifying noise levels in SASW measurements will provide a valuable tool for future research in assessing the resolution of final SASW results.