Abstract: It is an effective technique to treat inhomogeneous media as perturbations on the back ground of homogeneous media and to treat the perturbations as equivalent source. Two forms of corresponding integral equations are: 1) boundary integral equation with both boundary integral items for boundary displacement and volume integral items for displacement in wavefield; 2) volume integral equation including integral only for inhomogeneous bounded region. Much work has been done in this field. Interpreting inhom...