Re: Gravfft - Parker expansion

While Parker did not allow variable density, the method can accommodate it.  For instance, see http://dx.doi.org/10.1016/0012-821X(90)90078-C
We might want to deal with this at some point.

-p

On Feb 10, 2014, at 8:31 AM, J. Luis <[email protected]> wrote:

> 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
> 
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