Tilt Derivative Script (tilt_calc3)

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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.*#0160; 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., +/‐*#0160; tan[SUP]‐1[/SUP] (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*#39; 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.

Input magnetic anomaly grid (click to enlarge)

Output GDB with calculated depths (click to enlarge)

Grayscale map produced by script with depth locations from GDB plotted as proportional symbols*#0160;(click to enlarge)