Improving surface-wave group velocity measurements by energy reassignment
Improving surface-wave group velocity measurements by energy reassignment
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DOI：
10.1190/1.1567238
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发表时间：
2003-03
期刊：
影响因子：
3.3
通讯作者：
H. Pedersen;J. Mars;P. Amblard
中科院分区：
文献类型：
--
作者：
H. Pedersen;J. Mars;P. Amblard
表面波越来越多地用于浅层地震勘探，特别是在声波测井、环境和工程应用中。这些波是色散的，其色散曲线用于获得随深度的剪切速度剖面。其更广泛使用的主要障碍是相关数据处理和结果解释的复杂性。我们的目标是表明，能量重新分配的时间-频率域有助于提高精度的群速度测量的面波。为了说明这一点，全波形地震记录添加白色噪声的浅层平坦的地球模型进行了分析的经典和重新分配的多重滤波器分析（MFA）。经典的MFA给出了预期的群速度色散曲线的模糊图像，而重新分配的曲线给出了一个非常好的约束，狭窄的色散曲线。光谱衰减的系统误差在很大程度上通过重新分配程序得到校正。随后的反演的频散曲线，以获得剪切波速度与深度进行了线性反演与非线性蒙特卡罗反演相结合的程序。重新分配后获得的减少的不确定性引入了显着更好的约束地球模型比通过反转经典MFA的输出。最后进行了重新分配的数据从浅层地震调查在比利时北方，目的是确定剪切波速度的地震危险性评估。在这种情况下，重新分配也非常稳定。重新分配的使用可以使频散测量高度自动化，从而便于在浅层勘测中使用面波
Surface waves are increasingly used for shallow seismic surveys—in particular, in acoustic logging, environmental, and engineering applications. These waves are dispersive, and their dispersion curves are used to obtain shear velocity profiles with depth. The main obstacle to their more widespread use is the complexity of the associated data processing and interpretation of the results. Our objective is to show that energy reassignment in the time-frequency domain helps improve the precision of group velocity measurements of surface waves. To show this, full-waveform seismograms with added white noise for a shallow flat-layered earth model are analyzed by classic and reassigned multiple filter analysis (MFA). Classic MFA gives the expected smeared image of the group velocity dispersion curve, while the reassigned curve gives a very well-constrained, narrow dispersion curve. Systematic errors from spectral fall-off are largely corrected by the reassignment procedure. The subsequent inversion of the dispersion curve to obtain the shear-wave velocity with depth is carried out through a procedure combining linearized inversion with a nonlinear Monte Carlo inversion. The diminished uncertainty obtained after reassignment introduces significantly better constraints on the earth model than by inverting the output of classic MFA. The reassignment is finally carried out on data from a shallow seismic survey in northern Belgium, with the aim of determining the shear-wave velocities for seismic risk assessment. The reassignment is very stable in this case as well. The use of reassignment can make dispersion measurements highly automated, thereby facilitating the use of surface waves for shallow surveys