跨孔地震层析成像的级联方法

CASCADE APPROACH FOR CROSS-HOLE SEISMIC TOMOGRAPHY

对厚度小于1/4波长的超薄波速干扰体进行高分辨率成像,作者曾采用走时反演和波场反演相结合的方法,体现了由低分辨率向高分辨率逐步逼近的思想.级联算法是这种思想的进一步发展,我们将具有不同分辨率的算法串联起来,以达到高分辨率成像的目的.本文介绍一种三级串联的算法,并进行了算法分析,数值计算的例子说明这种级联算法分辨率高、稳定性好,只需要地震资料而不要求其它先验信息,因此能较好地满足实际应用的要求.

An inversion method which joins the tomographic inversions of traveltime and wavefield data have been proposed by authors for imaging earth with layers thinner than 1/4 wavelength. This method is characterized by the idea of successive approximation from low to high resolutions. The' further development of this idea is the cascade algorithm presented in this paper. Though several tomographic alogorithms, such as BPT, ART, SIRT, CGLS, LSQR and the inversion of the generalized Radon transform are available today, they all have advantages as well as defects, the algorithms of low resolution, such as BPT, enjoy low cost, stability and no requirement of prior knowledge about earth, they can be used first to provide initial earth model for higher resolution algorithms. The LSQR or CGLS algorithms may be used to produce a seismic velocity field, which can be further used as the reference velocity field in the inverse scattering methods, to produce a high resolution earth image by employing the inversion of rhe generalized Radon transform. In this manner, the proceed of seeking for solution in the solution space will take a correct route.Numerical analysis of the cascade algorithms is given together with some examples of application to fault mapping.