三参量速度分析的迭代算法

Iteration algorithm for three-parameter velocity analysis

采用预求倾角法进行三参量速度分析时,首先要确定地下界面的倾向和倾角。若没有准确速度,就求不准倾向和倾角,因此无法一次求得准确的结果。若采用迭代算法,则可以使三参量逐渐向精确值逼近。在地层倾角小于45°的情况下,迭代是收敛的。在有噪音的情况下,噪音会使叠加道集上同相轴的时间发生变化,从而影响倾向的确定,因此在迭代的每一步,都必须估算倾向。理论模型和实际资料的试算表明,采用迭代方法求取地下界面参数是切实可行的,它使三参量速度分析的结果明显优干常规速度分析。

The dip direction and dip angle of a subsurface interface must be first determined in three-parameter velocity analysis that needs predetermined dip angle. Accurate dip direction and dip angle can not be calculated without exact velocity, so that correct result can't be obtained once. The use of the iteration algorithm makes the three parameters gradually approach their accurate values. The iteration converges when dip angles are lower than 45 degrees. When there are noises,they distort the event times in the stacked gathers and cause erroneous dip direction; therefore, dip direction must be estimated in each iteration. Theoretical and real data trials show that this iteration algorithm is feasible in calculating the parameters of subsurface interface, and makes the three parameter velocity analysis result much better than conventional ones.