Thanks for the excellent tutorial! Just one thing about the topography and the Bouguer anomaly. If the background (white area above the topography in the model) is given the density of the Bouguer slab and terrain corrections, the effect of the topography on the calculated gravity profile should disappear almost completely. In the free-air anomaly the high correlation with topography is the product of the huge lateral density contrast between air and rock (so the backgroud should have density of air). When we apply the terrain correction and the Bouguer slab correction, it is equivalent to setting a background of the same correction density in order to remove the effect of topographic masses, so any lateral density contrasts beneath the surface are revealed. In summary, what we make cero is not the density of the topography, but the strong lateral density contrast of everything above the surface againts the topography, because this contrast is masking the density contrasts happening underground. Hope this explanation clarifies certain confusions. We should always be able to make density contrasts finish at the surface according to the outcropping surface geology. The concepts of the different anomalies can be tricky. For a nice review of the concepts I recommend the tutorial of Li and Goetze, (2001) in Geophysics, Vol. 66, No.6. For a very quick read on the gravity method and corrections I recommend the tutorial of David Chapin in The Leading Edge, May 1996. Best regards, Evert .
hi. thanks for the explication. sorry if this sound annoying but I need help, can you pass me you email if I have other questions about the tutorial that you mentioned.
+Music4Evert Hi Evert. Thank you so much for your response and sorry for taking so long to reply to it! I think I was just avoiding a topic that always confused me, but now with your explanation makes sense. I like your explanation "we want to zero the strong lateral density contrast of everything above the surface against topography". I will also take a look at your suggested articles. I ran 3 models to see the effect of: Model 1 - zero density background, topography of 2670 kg/m3 (free-air equivalent - see the effect of topography) Model 2 - 2670 kg/m3 background, topography of 2670 kg/m3 (bouguer equivalent - no topo effect) Model 3 - zero density background, zero density topography (bouguer equivalent) For anyone interested you can see the image at: drive.google.com/open?id=0B9In9AOnWyDRV0l6blppRVBQOFE So Model 2 or 3 can be used when modelling Bouguer data
No worries! The geophysical literature on the gravity method can be very confusing. Specially because of the different use geodesists and geophysicists do of the concept of a gravity anomaly. That's the reason I think Li and Goetze wrote the tutorial paper. Thanks again for the great tutorials.
Dear Stephanie, thanks a lot for your great lectures, and thanks for sharing with us. I am a PhD student. I am working on gravity modeling, and I have a topography grid for the Bouguer anomaly and also I have a topography from Global Terrain Mode for ocean and land. My model profile includes offshore and onshore data, and I need to understand how to deal with a water column. Please if you have time and could help me to properly deal with topography vs bathymetry in the model, I would highly appreciate it.
hallo Stephanie thanks for your tutorial It is very helpful Could you please tell me how to mark the slice zone like the one in your vidio I mean black lines on a map thank you
hello, I have a trouble with New Map--> From Map Profile and after I click it, notification show up, (The "nga_gms3d" dynamic object was found but could not be loaded. This affects the following functions : hlAzi)
Hi Stephanie, your videos are really informative and have helped me a lot. Do you know how to work the terrain correction function in Oasis Montaj? If so, can you make a video?
+Alicia Jayne McCabe Hi Alicia, thanks for letting me know, glad I could help! I haven't worked with the terrain correction unfortunately. Have you had a look at the tutorial: www.google.co.za/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0ahUKEwjl78LIuLzJAhXFtBQKHZvxAmYQFggyMAQ&url=https%3A%2F%2Fwww.u-cursos.cl%2Fingenieria%2F2011%2F1%2FGF700%2F1%2Fmaterial_docente%2Fbajar%3Fid_material%3D343733&usg=AFQjCNEjY3i1HkrsYEmy1W-WsG7uTBi2qg&sig2=pdfNoQN-l6uY8ZcS4zICYA
First of all thanks for the tutorial, but I have one concern... when you have Bouguer anomalies you removed a topography layer of uniform density, but there still remain bodies unaccounted for in this reduction, still sitting right underneath the topography, bodies which have densities equal to the density contrast between the terrain density that you removed and their own, bodies which are the source of the Bouguer anomaly. I am lost there when you say that there should not be any density there. Are we not trying to model for those density contrasts underneath the topography, not just bellow the datum? after all, with Bouguer correction we remove only part of the density above the datum, not all of it.
Hi Please I need step by step of 2D modelling magnetic and gravity data. I am a student of postgraduate school working on potential field and want to model my work. Please I need Your assistant. Thanks.
Moamen Almaz. Hi, so sorry I missed your question!!! it was a long time ago so I am sure you solved it. If not go to Map menu on the left of the menu bar > export > select viewed region on the right and the type of file you would like to export on the left (jpg). I usually set the dpi to between 150 and 300 depending on the output file size > then click export
Thanks for the excellent tutorial! Just one thing about the topography and the Bouguer anomaly. If the background (white area above the topography in the model) is given the density of the Bouguer slab and terrain corrections, the effect of the topography on the calculated gravity profile should disappear almost completely. In the free-air anomaly the high correlation with topography is the product of the huge lateral density contrast between air and rock (so the backgroud should have density of air). When we apply the terrain correction and the Bouguer slab correction, it is equivalent to setting a background of the same correction density in order to remove the effect of topographic masses, so any lateral density contrasts beneath the surface are revealed. In summary, what we make cero is not the density of the topography, but the strong lateral density contrast of everything above the surface againts the topography, because this contrast is masking the density contrasts happening underground.
Hope this explanation clarifies certain confusions. We should always be able to make density contrasts finish at the surface according to the outcropping surface geology. The concepts of the different anomalies can be tricky. For a nice review of the concepts I recommend the tutorial of Li and Goetze, (2001) in Geophysics, Vol. 66, No.6. For a very quick read on the gravity method and corrections I recommend the tutorial of David Chapin in The Leading Edge, May 1996. Best regards, Evert .
hi. thanks for the explication. sorry if this sound annoying but I need help, can you pass me you email if I have other questions about the tutorial that you mentioned.
+DucamiGalat ¡Chévere! Por favor envíame un mensaje privado y compartimos correos. Saludos :)
+Music4Evert Hi Evert. Thank you so much for your response and sorry for taking so long to reply to it! I think I was just avoiding a topic that always confused me, but now with your explanation makes sense. I like your explanation "we want to zero the strong lateral density contrast of everything above the surface against topography". I will also take a look at your suggested articles.
I ran 3 models to see the effect of:
Model 1 - zero density background, topography of 2670 kg/m3 (free-air equivalent - see the effect of topography)
Model 2 - 2670 kg/m3 background, topography of 2670 kg/m3 (bouguer equivalent - no topo effect)
Model 3 - zero density background, zero density topography (bouguer equivalent)
For anyone interested you can see the image at: drive.google.com/open?id=0B9In9AOnWyDRV0l6blppRVBQOFE
So Model 2 or 3 can be used when modelling Bouguer data
No worries! The geophysical literature on the gravity method can be very confusing. Specially because of the different use geodesists and geophysicists do of the concept of a gravity anomaly. That's the reason I think Li and Goetze wrote the tutorial paper. Thanks again for the great tutorials.
Dear Stephanie, thanks a lot for your great lectures, and thanks for sharing with us.
I am a PhD student.
I am working on gravity modeling, and I have a topography grid for the Bouguer anomaly and also I have a topography from Global Terrain Mode for ocean and land.
My model profile includes offshore and onshore data, and I need to understand how to deal with a water column.
Please if you have time and could help me to properly deal with topography vs bathymetry in the model, I would highly appreciate it.
Muito boa a apresentação....
Great
I look for the other video you have talken about in this video about import the borehole and how to complete the model plz.
I like your video. thank you so much. Could you show us deeply the starting point to draw modeling, it may be from electrical modeling?
thank you, its so usefull
Could you please give a short video on how to do Terrain correction of Gravity data on Geosoft
hallo Stephanie
thanks for your tutorial
It is very helpful
Could you please tell me how to mark the slice zone like the one in your vidio
I mean black lines on a map
thank you
Hello,
I like you video. Could you please a short video about griding a gravity or magnetic data!?.
happy new year!
+Saad Alarifi Hey...sorry for taking so long to do this: ua-cam.com/video/8608kC9_Dg8/v-deo.html
hello, thank you very much for your tutoriel. plz can you explain how we can add a fault in GMSYS software :)
Hello everyone, I want to create a geologic model from my ground magnetic profile data using the GM-SYS tool. How do I go about it?
hello, I have a trouble with New Map--> From Map Profile and after I click it, notification show up, (The "nga_gms3d" dynamic object was found but could not be loaded. This affects the following functions : hlAzi)
Hi Stephanie, your videos are really informative and have helped me a lot. Do you know how to work the terrain correction function in Oasis Montaj? If so, can you make a video?
+Alicia Jayne McCabe Hi Alicia, thanks for letting me know, glad I could help! I haven't worked with the terrain correction unfortunately. Have you had a look at the tutorial: www.google.co.za/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0ahUKEwjl78LIuLzJAhXFtBQKHZvxAmYQFggyMAQ&url=https%3A%2F%2Fwww.u-cursos.cl%2Fingenieria%2F2011%2F1%2FGF700%2F1%2Fmaterial_docente%2Fbajar%3Fid_material%3D343733&usg=AFQjCNEjY3i1HkrsYEmy1W-WsG7uTBi2qg&sig2=pdfNoQN-l6uY8ZcS4zICYA
First of all thanks for the tutorial, but I have one concern... when you have Bouguer anomalies you removed a topography layer of uniform density, but there still remain bodies unaccounted for in this reduction, still sitting right underneath the topography, bodies which have densities equal to the density contrast between the terrain density that you removed and their own, bodies which are the source of the Bouguer anomaly. I am lost there when you say that there should not be any density there. Are we not trying to model for those density contrasts underneath the topography, not just bellow the datum? after all, with Bouguer correction we remove only part of the density above the datum, not all of it.
Hello! How can I export my model as pdf or image? thanks
How can I create the profile?
Can you help me please 😢
Hi Please I need step by step of 2D modelling magnetic and gravity data. I am a student of postgraduate school working on potential field and want to model my work. Please I need Your assistant. Thanks.
What is the best way to export the model to be presented on a poster or in a thesis.
Moamen Almaz. Hi, so sorry I missed your question!!! it was a long time ago so I am sure you solved it. If not go to Map menu on the left of the menu bar > export > select viewed region on the right and the type of file you would like to export on the left (jpg). I usually set the dpi to between 150 and 300 depending on the output file size > then click export
Thanks for the tutorial , but still I have some queries can you give me any mail id so that I can consult there for further doubts
Hello everyone, I want to create a geologic model from my ground magnetic profile data using the GM-SYS tool. How do I go about it?