Agree!
The Geosoft gravity module is handy for performing data reductions using a 
range of Bouguer and terrain densities prior to Voxi inversion. A 
Nettleton-like series of profiles can quickly be generated over a feature of 
interest graphically using profile views, or even for the whole dataset, to 
determine what reduction density might be most appropriate prior to inversion. 

Not determining an appropriate reduction density prior to an inversion for say 
a cover sequence might produce topo-related artifacts in the inverted model, so 
if the time's available running a suite of densities and inversions could be 
recommended.  
Cheers
Ed
 

    On Tuesday, September 20, 2016 9:01 AM, author.nameemail 
<geonet@lyris.geosoft.com> wrote:
 

 Thanks for the clarification.
Regards
Ana

-----Mensagem original-----
De: DarrenAndrews <darren.andr...@geosoft.com> 
[mailto:geonet@lyris.geosoft.com] 
Enviada: terça-feira, 20 de Setembro de 2016 15:52
Para: Geosoft Oasis montaj and Target
Assunto: RE: [geonet] Modelling complete bouguer anomaly in VOXI and density 
values

Hello Ana,

Your assumption is correct. If you are using Bouguer Anomaly data for the 
inversion, then in order to get estimates of "real" density, you will need to 
add the Bouguer density used in the complete Bouguer anomaly calculation.

When inverting gravity data, often we are trying to model what is a very small 
(the shallow crustal) component of the gravitational field. Reducing the data 
to the complete Bouguer anomaly enables us to isolate that component. 

In calculating the complete Bouguer anomaly, we provide a density that we 
assume is representative of the bulk density of the shallow crust we are trying 
to model. When modelling the anomaly data, we then assume that this is the 
"background" density. 

Density values returned from your voxi Inversion are relative to this 
background value. If you think that 2.67g/cm3  is an appropriate background 
density for your area of interest then this is the right density to use both in 
the Bouguer calculation and also to add to your voxi results.

If you think that an alternative density value is appropriate for your area of 
interest, then you should re-calculate your complete Bouguer anomaly using that 
density and then run your inversion with that data. It is common practice in 
gravity interpretation to calculate and interpret Complete Bouguer Anomaly data 
for several different densities, particularly if little is known about the 
geology of the area.

Best regards,

Darren Andrews
Technical Analyst | Geosoft
geosoft.com | blog | twitter | linkedIn | facebook | T +1 416.369.0111 #353 | M 
+1 647.272.7188

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-----Original Message-----
From: author.nameemail [mailto:geonet@lyris.geosoft.com] 
Sent: Tuesday, September 20, 2016 9:52 AM
To: Geosoft Oasis montaj and Target <geonet@lyris.geosoft.com>
Subject: [geonet] Modelling complete bouguer anomaly in VOXI and density values

Hello,

I used complete bouguer anomaly data for the gravity inversion in VOXI and now 
I have a density model. I also considered the topography and used a DEM grid.
My question is related to the range of density values of the model, because I 
have a range of negative and positive values (-0.29 to 0.42 g/cm3). 
So it seems that I have to add the bouguer density used in the data correction 
(2.67g/cm3) to have a real density range.
Can someone help me to clarify this issue... 

Best regards,
Ana

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