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Clayton和Engquist曾提出波动方程偏移时用的吸收边界条件。文章认为,其中一个边界条件,即45°(三阶)偏移方程采用的B2(二阶)条件是属于不适定的边界条件。事实上,这一边界条件具两个明显不同的不适定性机制:其一是,在某一个边界上波具有有限速度传播的Kreiss模式,而另一种是波在两个边界间以无限制速度往返传播的一种新模式。与B2不同,三阶Clayton-Engquist边界条件B3是适定的。但是,对于采用高于三阶的偏移方程来说,文章认为高于一阶型的Clayton-Engquist任何边界条件不可能是适定的。
Clayton and Engquist have proposed absorption boundary conditions for wave equation migration. It is considered that the B2 (second order) condition adopted by one of the boundary conditions, that is, the 45 ° (third order) offset equation, is an ill-defined boundary condition. In fact, there are two distinct ill-posed mechanisms for this boundary condition: one is the Kreiss mode with limited velocity propagation on one boundary and the other is the wave propagation at the infinite speed between the two boundaries A new model of round-trip communication. Unlike B2, the third-order Clayton-Engquist boundary condition B3 is suitable. However, for an offset equation higher than third order, the article considers that any boundary conditions higher than the first order Clayton-Engquist can not be fitted.