Non-uniqueness in near-surface refraction inversion
Non-uniqueness,which is a fundamental reality with the inversion of all near-surface seismic refraction data,occurs with the 1D parameterization of the traveltime graphs in the vertical dimension and with the 2D lateral resolution of individual layers in the horizontal dimension.This study focuses on the non-uniqueness in the lateral resolution of individual layers which results from the application of 1D,1.5D and 2D inversion algorithms to generate starting models for wave eikonal traveltime (WET) tomography.The automatic parameterization of the traveltime graphs in terms of 1D vertical velocity profiles with the 1D tau-p algorithm can generate artifacts where there are simple departures from 1D i.e.,planar,refractors.These artifacts prevent the detection of any genuine lateral variations in seismic velocities which are representative of shear zones.The efficacy of the 1D tau-p lgorithm to reliably define 2D refractors is questionable.Normally,the lateral resolution of the time structure of individual layers is much the same with 1.5D and 2D algorithms.Therefore,the major source of non-uniqueness is usually in the determination of the lateral variations in the seismic velocities within each refractor.This study demonstrates that WET tomography does not necessarily generate reliable images of the subsurface with 1D and 1.5D inversion algorithms.The 1D tau-p algorithm can generate artifacts and lack lateral resolution while the 1.5D algorithms can also generate artifacts.Therefore,it is recommended that 2D inversion algorithms,rather than the 1D algorithm,should be the default for generating starting models for all tomographic inversion.In most cases,1D and 2D analyses of head wave amplitudes can resolve ambiguities.It is concluded that the routine analysis of head wave amplitudes,which constitute readily available a priori information,is the most effective step for improving the performance of all near-surface seismic refraction methods.
Derecke Palmer
The University of New South Wales,Sydney 2052,Australia
国际会议
The 3rd International Conference on Environmental and Engineering Geophysics(第三届环境与工程地球物理国际会议)
武汉
英文
42-54
2008-06-15（万方平台首次上网日期，不代表论文的发表时间）