water column

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freitag
Posts: 10
Joined: Wed Sep 09, 2009 2:21 am

water column

Postby freitag » Sun Jan 09, 2011 8:47 pm

Hi Marc,

I was trying to invert dispersion curves from an oceanic region. However, dinver gets stuck when the S-velocity of the first layer is set to zero. Is there any way that dinver can handle a water layer at the top?

Cheers,
Yannik

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Postby admin » Fri Jan 21, 2011 9:45 am

This is one improvement of the forward computation code that can be foreseen. I had discussions some years ago about that and I also tried to set a null Vs but it does not work so easily. I generates divisions by zero in the current formulation of the problem. If you take Aki & Richard matrices for Rayleigh waves with a null Vs it does not work either. Surface waves measured with a fluid cap are called Stoneley waves and they requires a slightly different formalism. Codes from Robert Herrmann have or had an option for an ocean/sea layer. A similar computation should be introduced in gpdc/dinver codes. However, if you have some literature references about that topic there are pretty welcome. Personally, I have had not time yet to concentrate on that implementation but if you feed me with some references, things can be sped up.

freitag
Posts: 10
Joined: Wed Sep 09, 2009 2:21 am

Postby freitag » Wed Feb 09, 2011 9:27 pm

Hi Marc,

Sorry for my latish reply. I just saw that you were discussing to include Saito's code into dinver in a separate thread. As this code can also handle liquid layers you could kill two birds with one stone. I further found some remarks on this problem in Aki and Richards (2nd edition; Chapter 7.2; Box 7.6). They refer to Gilbert, F., 'Elastic waves in a transitional solid with arbitrarily small rigidity", GJI, 133, 1998 for a more detailed discussion.

Not sure if this helps.

Cheers,
Yannik


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