[CIG-SEISMO] Mineos problem

[Andrew Valentine]

Hi all,

There are known problems with Mineos, which is built around various early (and somewhat bespoke) numerical routines. Unfortunately computing eigenfunctions and eigenfrequencies of earth models is somewhat complex, and it isn’t as simple as switching to a modern Lapack solver. Work is in progress to implement a replacement for Mineos (see, e.g., http://www.geo.uu.nl/~andrew/talks/talk_egu2015.pdf), but this is not ready yet.

I think there are some posts from Martin van Driel in the archive of this mailing list that describe some of the problems in more detail.

A number of the numerical issues can be reduced - but not completely eliminated - by generating a 1D model input file that has a finer grid spacing. (The versions of PREM distributed with Mineos are sampled on 185 knots, but it is straightforward to create versions with a higher number of samples.) This tends to improve the integration stability, and also reduces errors that arise during normalisation of eigenfunctions. If it is desired to increase the number of knots by more than a modest amount, it will be necessary to increase the size of the arrays Mineos uses as memory buffers.

All the best,
Andrew




> On 03 Mar 2016, at 16:00, Matthew Knepley <knepley at rice.edu> wrote:
> 
> We have a problem with the eigenfunctions calculated by Mineos at near degenerate eigenvalues.
> 
> Mineos works fine to calculate the eigenfrequencies of normal modes, but there is a problem for the eigenfunctions. For those different modes with very close eigenfrequencies in the mathematical point of view(see Figure f-l), Mineos regards them as degeneracy in the numerical point of view, and therefore it gets a linear combination of pure R mode's and pure Stoneley mode's eigenfunctions, i.e. the eigenfunctions are not orthogonalized. For example, based on Okal's classification [1], 2S25  and 3S25 should be Stoneley mode and R mode, respectively. But the eigenfunctions from Mineos have both surface oscillations (the feature of R modes) and exponentially decaying along CMB (the feature of Stoneley modes).(see Figure 2S25 and 3S25)
> 
> Since the eigenfunction is not calculated properly, the group velocity is also not reliable. According to Okal's paper [1], for each branch of R modes or Stoneley modes, the group velocity should be continuous. And we notice that there are some "bad points" in the group velocity picture, which are exactly the modes we mention before. (see Figure groupV_R2)
> 
> What eigensolver is being used inside Mineos? The standard symmetric eigensolvers in LAPACK handle this problem I believe.
> 
>   Thanks,
> 
>     Jingchen and Matt
> 
> References:
> 
> [1] Okal, Emile A. "A physical classification of the earth's spheroidal modes." Journal of Physics of the Earth 26.1 (1978): 75-103.
> 
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-- 
Dr Andrew Valentine
Postdoctoral Researcher

Department of Earth Sciences, Universiteit Utrecht
Postbus 80.115, 3508TC Utrecht, The Netherlands
+31 (0)30 253 5192  -  www.geo.uu.nl/~andrew