用于速度图象重建的层析成象法

本文提出了一种用于速度图象重建的层析成象法。特别注意到地震学上的ST与医学上的CT的不尽相同之处,并处理了由此引起的困难。与速度图象重建有关的正问题的分析表明,不同频率范围的资料其分辨能力是不同的,因此,区域地震与远震资料的解释应予注意。本文有关速度图象重建的讨论不仅涉及到与成象方法有关的反演理论和方法,还给出了进行数值计算的内存量和运算量的分析。关于重建图象的质量评价,还给出了反演解的可靠性分析,为分辨特性的描述提供了一种既简便又形象直观的方案。 本文的方法与现行主要方法的比较表明:1.本文的方法允许存在速度间断面,有利于揭示不同构造区域的地壳厚度的差异;2.在常用的方法中,作为正问题假定的常速度块同反演结果解释时非常速度块之间不协调。由于我们把给定网格点的速度值的插值函数作为速度的空间函数,这一困难已被解决;3.相对于Aki等的一般方法,本文的内存量节省约一个量级、运算量减少约一半;4.相对于ART类方法本身不能给出成象结果的可靠性分析,本文的方法则具有显著的优点。 作者在分析了天然地震资料的状况之后相信,对充分利用我国地震台网的现有观测资料,本文的方法是有效的。

ON THE TOMOGRAPHIC INVERSE METHOD USED IN VELOCITY IMAGE RECONSTRUCTION

A new kind of tomographic inverse method used in velocity image reconstruction has been put forward in this paper. The authors especially notes that the ST （Seismic Tomography） of seismology and the CT （Computerized Tomography） in medicine are not identical in some respects and we try to deal properly with these difficulties. The analysis of forward problems concerned with velocity image reconstruction shows that the resolving power of the data of different frequency domains is different. Therefore, this difference should be noted in the interpretation of data from regional and distant earthquakes. The discussion here about the velocity image reconstruction involves not only the inverse theory and method telated wth tomographic inversion, but also the analysis for memory storage and operation requirements of the numerical calculation. As for the evaluation of the quality of image reconstruction the authors give the analysis for reliability of the inverse solution which provides a simple, convenient and audio-visual scheme.A comparison of the method of this paper with the chief methods ordinarily used shows that: 1. the velocity discontinuity surfaces permitted to exist in this paper is favourable to reveal the discrepancy of the crustal thickness in different tectonic provinces; 2. the inconsistency between the constant velocity blocks as presumed in the forward problem with the inconstant velocity blocks in the interpretation of inverse results used in ordinary methods has been overcome by the use of interpolation function of the grid velocity as the space function of the velocity in parametrizing the model; 3. as compared with the general methods of Aki et al. the memory storage required in this paper is about an order of magnitude smaller and the amount of computation is reduced to about one half; 4. and compared with the ART methods, which can not give the reliability analysis of the tomographic results, the method of this paper has an outstanding advantage in this respect.