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变网格间距速度层析成像,是指反演网格模型中采用不同的网格间距反演地下地层的速度分布,它可以在观测数据较少的情况下,提高浅部地层速度反演的分辨率和深层速度反演的精度。变网格间距与规则网格间距速度层析成像方法类似,但有两个最主要的不同之处:射线正演网格单元的射线段被划分到相应的较大反演网格单元中,平滑约束方程在变网格间距界面的上一平面和下一平面的网格处需要做出适当的修改。文中首先采用变网格方法对二维和三维检测板模型进行恢复测试,反演结果对大、小异常体的刻画效果均比规则网格方法好;然后,采用变网格方法对实际资料进行走时反演,反演结果对两个低速异常区的刻画比规则网格方法的效果好。因此,变网格方法反演的速度剖面分辨率较高,尤其对浅部地层的速度成像效果具有较大的改善作用;另外,在观测数据较少的情况下,通过调整不同网格的数量比例,变网格反演方法还可以克服层析成像过程中解的欠定问题。
Variable grid spacing velocity tomography refers to the inversion of the velocity distribution of the underground formation using different grid spacings in the inversion grid model. It can improve the inversion of shallow formation velocity with less observed data Resolution and accuracy of deep velocity inversion. The variable grid spacing is similar to the regular grid spacing velocity tomography method, but has two main differences: the ray segments of the forward beam grid elements are divided into corresponding larger inversion grid elements, Smoothing Constraints Equation The appropriate changes need to be made at the grid of the previous plane and the next plane of the variable mesh spacing interface. In this paper, we first use the variable mesh method to test the two-dimensional and three-dimensional test board model. The inversion results are better than the regular grid method for the characterization of large and small anomalies. Then, Travel time inversion, the inversion results of the two low-rate anomalous zone characterization than the regular grid method effect. Therefore, the resolution of the velocity profile retrieved by the variable mesh method is high, especially for the velocity imaging effect of the shallow strata. In addition, with less observed data, by adjusting the number of different meshes Proportional and variable mesh inversion methods can also overcome over-commitment in tomographic imaging.