In our recent webinar on using 3D potential-field modelling to help evaluate a geothermal prospect, Gerry Connard demonstrated how to take advantage of lesser-known Oasis montaj features such as the Tilt Derivative script when creating models in GM-SYS 3D.
This script makes use of the derivation by Rick Blakely (see the technical note Tilt Derivative Made Easy) that shows that 1/tilt_HD = depth‐to‐source along the zero contour of the tilt derivative. Remember that the input grid needs to be RTP.
The script does the following:
- Calculates the tilt derivative (Ɵ) and horizontal gradient of the tilt derivative (dƟ/dh ) using the MAGMAP tiltdrv.gx
- Displays Ɵ using a grayscale zone file (tilt2.zon) that colours the grid between +/‐ 0.4636476 radians (i.e., +/‐ tan‐1 (1/2) for z/2) gray and everything else white
- Draws the zero contour on the grayscale map
- Exports the contour to a shapefile
- Imports the shapefile into a GDB named "pts_tilt0_lnz_Shapes.gdb" (the other "pts.gdb" database can be deleted)
- Re‐fids the points in the GDB to their "nominal' distance to reduce gaps
- Samples the dƟ/dh grid along the zero contour
- Runs a database math expression to calculate a depth channel =1/ dƟ/dh
You can get the contour location into a GDB by exporting the contours to a shapefile. Note that the "Depth" channel is the depth below the flight elevation.
The images below show an example of this script run on the Warner Valley magnetic data.