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.

*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 (click to enlarge)*

There are a number of Help topics that cover how to create and run a math expression in a database. This one is a good place to start: https://my.seequent.com/support/help/oasismontaj-workflow-content_ss_edit_preprocess_data_apply_mathematical_expressions_c_math_expression_builder.htm. There is also a video that shows this in action: https://my.seequent.com/support/video/378

Posted by: Natalie | 16 January 2020 at 09:32 AM

How to runs a database with math expression of depth calculate?

Thank you

Posted by: Firhan Maulana | 16 January 2020 at 12:40 AM

The steps for tilt derivative script are outlined in the the technical note "Tilt Derivative Made Easy" (https://www.geosoft.com/media/uploads/resources/tilt_derivative_made_easy_07-2016.pdf). For more on scripting, check out "Scripting in Oasis montaj" (https://my.geosoft.com/supportcentre#/video/1157)

Posted by: Natalie | 04 September 2019 at 09:51 AM

Hi can you please send me the tilt derivate script for calculating depth to source edges

Posted by: Ismael Zaaruka | 04 September 2019 at 06:04 AM