Hello everyone,
Which method is the best when presenting HEP of subsurface resistivity data, pseudosections ? ,2D- data levels ? Or depth sections ?, and why?
Regards
Hello Dr Wadhah Mahmood,
Actually I didn't understand your question completely. But, if you mean which method (or profiling method) is the best for showing the lateral changes of subsurface anomalies, the answer is the dipole-dipole profiling. The output to resistivity profiling (Weiner, Dipole-Dipole, Pole-dipole or etc) is an apparent resistivity section, which can be converted to the actual resistivity using finite difference modelling softwares such as RES2DINV.
Actually, if this is not your question, fill free to ask your question in more details. We had done an electrical resistivity study for a site selection project in Erbil, Iraq, in 2014, and I have a little knowledge in this area of science. I will be happy if I could share it to you.
Best Regards
Hamzeh
Dear Dr. Gheymasi,
My question was not about the type of configuration or array used or the method applied. It was about the display graphs of profiles , which one is the best to give the best visualization is that the 2D depth sections with the missing sides? or the pseudosection or spacing section?.
Regards.
Dr. Wadhah
Dear Mr Wadhah Mahmood Shakir Alkhafaji,
The best visualisation is the 2D depth section, including topography (if there is any). The missing triangles at the sides are left out because they do not contain measurement data. The pseudosections are there for you to check if the inversion process gave satisfactory correspondence between measurement and model and also to check in which parts of the profile you might distrust the inversion result.
Best regards,
Koen
Thank you, Mr. Koen Verbeeck for your answer,
as I understand both sections should be available side by side to give a more accurate visualization of subsurface resistivity.
Regards
Wadhah
Dear Mr Wadhah Mahmood Shakir Alkhafaji,
In a publication it should suffice to put only the modeled 2D section if you also mention the number of iterations and the RMS error value between the measured pseudosection and the pseudosection corresponding to your modeled 2D section.
In the measured pseudosection each measured resistivity is simply plotted in the middle of the electrode layout involved in that measurement and at a fixed depth that is calculated from the distances (a and n values) between the electrodes.
The pseudosection calculated from the 2D model takes into account the entire current path (volume of ground) that is involved in each of the measurements.
The initial 2D model is based on the measured pseudosection but each iteration the 2D model is changed to minimise the RMS error between measured and model pseudosection. The final 2D model should then be a relatively good representation of the real resistivity distribution in the subsurface.
Furthermore via the RES2DINV inversion settings you can select different ways the 2D model is be adapted in each itteration or different inversions methods:
-Normal inversion (smoothness-constrained inversion) gives smooth resistivity changes without sharp contacts and is interesting to see gradual changes;
-Robust inversion reduces the effect of outlier data points, gives sharp interfaces between homogenous rectangular geological bodies and is interesting when sharp resistivity contacts are expected (bedrock, sediments);
-Combined inversion (ridge regression with smoothness-constrained inversion) avoids distortion of current paths due to large resistivity contrasts and is interesting for a survey on a very low or very high resistivity body.
Each of those inversions provides a slightly different final 2D model of the subsurface resistivity distributions. So to give an accurate visualisation of the subsurface resistivity and the different possible interpretations it may be best to show the final 2D models of the normal, robust and combined inversions of the same section side-by-side.
A good tutorial on 2D and 3D resistivity measurements is: https://pangea.stanford.edu/research/groups/sfmf/docs/DCResistivity_Notes.pdf
Best regards,
Koen
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