Depth estimation using PETER HALF SLOPE METHOD in oasis montaj

Posts: 2
Hello,
I would like to calculate the depth to basement using PETER HALF SLOPE METHOD in oasis montaj. i would like to know if i can and how ?
Best regards

• Posts: 338 mod
Hi @abdellahnaitbba I'm not familiar with The Peter Half Slope method. Do you have a paper reference that describes it? Our Depth to Basement extension gives you three options. They're described in this tech note: http://www.geosoft.com/media/uploads/resources/technical-notes/montaj_depthtobasement_technote.pdf.
Community Manager

• Posts: 74
@abdellahnaitbba
Peter's Empirical method to determine depth applies only to vertical magnetic tabular bodies. The onus is on you to determine which anomalies in your data qualify. As a result it is an interactive method where the user input and interpretation is key. The user must also have a priori knowledge of the depth-to-thickness ratio. The description can be found here: https://www.hindawi.com/journals/ijge/2014/306862/
There are other rule of thumb approaches to estimate the thickness and depth of magnetic bodies, which you can use along with Peter's depths, specifically for figuring out the depth to thickness relationship.

We do not have a specific tool to calculate depths using Peter's half depth method. If it is the depths that you are interested in you may want to try one of the methods listed in the previous attachment. If you intend to evaluate depths using specifically Peter's depth estimations you could use OM tools interactively along with your interpretive input.

Below is one suggested approach:
1. Reduce the mag data to the magnetic pole to make it easier to identify vertical bodies: 1D-FFT >Reduce to pole

2. Subtract the long wavelength to remove the regional slope. a) Run the non-linear filter to generate the regional field. b) Subtract it from the RTP

3. Calculate the derivative to identify the slope of the magnetic field

You may need to apply a few passes of the Hanning filter on the derivative to make it smoother

4. You can now run a simple comparative filter to identify where the maxima of the slopes occur and display it on the profile window so that you can move faster through the data.

5. Visually look through the lines, and identify nearly symmetrical anomalies indicating vertical tabular bodies. You can skip through the data by focusing only where you have symbols plotted that indicate the slope maxima. For each selected anomaly find the value in the Distance channel (a byproduct of filtering) for which the derivative drops to around half the maximum. You will find a distance value on either side of the maximum.

6. Subtract the 2 distance values to get the d value in the illustration below. Finally you have to figure out the Proportionality factor to scale the d value

Of course should you decide to run Peter's depths on a regular basis you could write a GX using the GX Developer to string this workflow together in a custom GX and improve on it.
Points 1 through 4 can be saved in a script. Points 5 & 6 could be tideous if done manually but can be written as a GX.

Technical Product Manager, Geophysical
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