绕射波物理性质的研究

A STUDY OF THE PHYSICAL PROPERTIES OF DIFFRACTED WAVES

本文通过超声波地震模拟实验及理论分析,对绕射波的一些物理性质进行了研究。所使用的环绕绕射棱的定向等距圆弧观测法,可以较肯定地辨认记录上的绕射波。实验证明折射绕射波与反射绕射波具有一些共同的特征。实验证明绕射波存在正、负两个半支。根据这一结果,合理地解释了短界面向“点界面”转变以及两个断块靠拢成一个连续界面时,两个断棱的绕射波因正、负反相重迭而抵消的现象,认为绕射波的强度主要与断棱附近一定宽度的条带有关,而地震界面的中断并不能使波动场中断,而只是由一种波转变为另一种波,这就是波动场的连续性、渐变性。文中将折射绕射波与反射绕射波统一起来研究,从而在较广泛的意义上建立统一的绕射波理论。此外,还从物理概念上对绕射波性质给以直观的解释,并指出地震资料处理中偏移技术的绕射扫描理论所存在的缺陷。

A study of the physical properties of diffracted waves has been made by means of ultrasonic model experiments and theoritical analysis. By putting the receivers in a circle around the diffracting edge, the diffractions can be observed and recognized with a yet higher cer-tainty. It hay been proved by experiments that the refractional diffrac- tions and the reflectional diffractions have much ,in common with each other. Experiments also proved that the diffractions consist of two parts, one of them is positive, and the other, negative. In line with this, an appropriate explanation about the cancellation of diffractions can be made naturally. As is well known to everybody, when two faulted bedding-planes are shifted to an interface of continuity or, when a section of interface is shortened gradually to a point, diffractions will be cancelled out. The energy of diffraction is determined mainly by a zone of definite width along the diffracting edge. The break of the seismic interface doesn’t imply the corresponding break in wave field,but the transformation of the wave from one type to another--that isthe principle of continuity of wave field.In this paper, an integrated study has been made for both the refractional diffractions and the reflectional diffractions, and an unified theory about diffractions has thus been built up. What is more,an audio-visual explanation about diffractions has been made and the insufficiency of the theory of diffraction scan used in migration has also been pointed out.