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引言经过正常时差校正的地震记录上波前的偏移,当与其有关的射线垂直于波前的矢量远远不是垂直时,是非常必要的。这种波前以某种视速度为特征,而根据该视速度可以算出射线的倾角。给出一个假设速度函数和一个射线出射时的角度,射线就能被追踪而返回初始点。这就是射线偏移的本质。在采用计算机以前,是用波前图和其他图解方法进行偏移的。经验说明,这些方法很不方便,因为对于每个新的速度函数都需要绘制一种新的图板。现在,用波动方程进行偏移普遍被应用了。波动方程偏移的基本原理是寻找下行和上行波前共同存在的那一点。这个点子就是上行波的初始点。对于反射波来说,它就是反射面的位置。在计算机上计算有限差分波动方程,完成了波的
INTRODUCTION The migration of wavefronts on seismic records corrected for normal time differences is necessary when the vector associated with them is perpendicular to the wavefront and is far from vertical. This wavefront is characterized by some apparent velocity, from which the inclination of the ray can be calculated. Given an assumed velocity function and the angle at which a ray emerges, the ray can be traced and returned to the initial point. This is the essence of ray migration. Before using the computer, is the use of wavefront diagrams and other graphical method of offset. Experience shows that these methods are inconvenient because a new chart needs to be drawn for each new speed function. Now it is common to use the wave equation for the offset. The basic principle of the wave equation migration is to find the point where the down-going and up-going wave fronts coexist. This idea is the initial point of the ascending wave. For reflected waves, it is the position of the reflecting surface. Calculate the finite difference wave equation on the computer and complete the wave