Re: Gravfft - Parker expansion

On 10-02-2014 14:32, Lester Anderson wrote:
> Hello,
>
> Quick query. When calculating the flexural "Moho" there does not seem 
> to be a way of applying anything but the default first term in 
> Parker's expansion, so anything beyond that (eg -E4) will generate a 
> warning message as below and the program continues with E1:
>
> c:\SS20-work>gravfft black1-topo.grd -Gblack1-topo_flex25km.grd 
> -T25000/2670/3330/1030 -Z32000 -V -fg -E3 -Q
> gravfft: Warning: Due to a bug, or a method limitation (I didn't 
> figure that yet) with the selected options, the number of terms in 
> Parker expansion is reset to one
> See examples in the manual if you want to compute with higher order 
> expansion
> *****
>
> This error/warning is mentioned in the documentation, but I was 
> wondering if there is a workaround if one needed to use higher terms 
> of the Parker expansion in flexural studies, or is the first term 
> sufficient?

First, let me state that those are old notes that I wrote at the time of 
first versions of gravfft and they are not so ... fresh now, but I note 
that the same doc that you refer also say

"...For higher powers of bathymetry in Parker expansion, only the above 
example seams to give the correct result."


>  As with all these things, setting the mean Moho depth and a constant 
> density contrast is a big oversimplification.
>
> Is it feasible to compile a variable density grid for flexural studies?

It's always educative to read the original papers.
No, Parker method does not allow a variable density across the interface.

Joaquim


To unsubscribe, send the message "signoff gmt-help" to [email protected]