[CIG-SEISMO] Mineos problem

[Guust Nolet]

I am not a Mineos expert, but I think one should consider the physical reality of degenerate modes and not remain focused on the numerics. If two modes are truly degenerate, *any* combination of the regular mode and the Stoneley mode is an acceptable eigenfunction. I assume your Mineos eigenfunctions do satisfy the equations and boundary conditions and are not perse wrong, you just get something you do not want.

One could counter that the modes are only degenerate to numerical precision, but that ignores the fact that in the real, attenuating Earth, the modes have a finite width, so that frequencies probably overlap even with exact calculus. Of course one could formulate the eigenproblem for an attenuating medium, but that is not what Mineos does and I do not think anyone has considered it worthwhile to program such a problem.

But I suggest that if you wish to separate the two into modes with Stoneley vs. regular character, you should just optimize some quality (e.g. energy near the CMB) and get the linear combination of the two modes you want for the Stoneley mode, then find the second mode by orthogonalization.

Best wishes,

Guust Nolet
https://www.geoazur.fr/GLOBALSEIS/nolet/