A Thorough Search of Normal Modes For the Ocean-Earth Model

Abstract:

Built upon generalized reflection/transmission coefficients, a family of secular functions constructed based on the continuity conditions across various interfaces, have been proposed in our previous study to give a thorough search of normal modes for stratified layered model. For the ocean-Earth model, i.e., one with a stack of surficical fluid layers, we find that the secular function constructed according to the continuity condition across the fluid/solid interface, which is devised specially for finding Stoneley modes especially at high frequencies, should be employed as well to find a few “stubborn” modes that may otherwise probably be lost with the searching step fixed. It turns out that these “stubborn" modes belong to the so-called trapped modes whose energy are mainly focused in the layers other than in the low-velocity layers. Were our searching scheme not employed, the searching step would become much finer and it would thus cost more time, and no loss of these “stubborn” modes would not even be guaranteed, if the traction-free condition alone was used to find the physically existent modes at given frequency. This demonstrates again the necessity and effectiveness of our proposed mode-searching approach when the model contains low-velocity layers or fluid layers.