Dear Ayaz Mohmood Dar, glad to meet you.

Magnetic math data filtering, such as the tilt-derivative filter as you are interesting, depending on your specific goals. The general purpose of any filter “is to enhance anomalies of interest and/or gain some preliminary information on source location or magnetization” (Nabighian et al, 2005).

According with your question, I understand that you are interested in the edge or imaging of the fault-system, in your study-case a thrust fault-system, and therefore, I recommend to you to apply the tilt-derivative filter in combination with another geometrical attribute, such as the total gradient (AS, Analytical Signal), curvature, complete horizontal gradient, first and second vertical derivatives, etc, to emphasize the edges of the faults. Also, I recommend applying it not only over the total magnetic grid, but also in the residual one.

As you know, the tilt-derivate (angle) by Miller and Singh (1994), is the ratio of the first vertical derivative to the horizontal gradient and is designed to enhance subtle and prominent structures. Lastly, a form of filter that can be used to highlight faults is the Goussev filter, which is the scalar difference between the total gradient and the horizontal gradient (Goussev et al., 2003). This filter provides supports to categorize between contacts and simple offset faults. Wrench faults show up principally well as breaks in the linear patterns of a Goussev filter.

In Geosoft, you must go to the TILTDRV GX to calculate the till-derivative of a grid, or use the option MAGMAP ---> Tilt Derivative, and optionally the total horizontal derivative of the tilt-derivative grid. Also, remember that due that the answer is in radians/distance units, the grid should be put in distance (e.g., meters) instead grades (latitude and longitude, in grades).

Please, let me know if you need an specific help in the step-by-step solution, I can help you.

Best wishes, Mario E. Sigismondi

Dear Ayaz Mohmood Dar ,

Tilt derivative is an interpretation method that is used to determine the edges of source bodies utilizing gravity and magnetic data. The value of the tilt derivative varies between +pi/2 and -pi/2.

For the edge detection and to calculate the source depth, you have to plot the contours of +pi, -pi and 0. Theoretically, zero contour lies directly over the source body. By utilizing this and comparing it with the previous known structure you can delineate subsurface structural lineaments.

Also, you can calculate the source depth by calculating the half distance between the contours of +pi/4 and -pi/4.

For further you can read the following papers:

1. A. Salem, S. Williams, J. D. Fairhead, D. Ravat, and R. Smith, “Tilt-depth method: a simple depth estimation method using first-order magnetic derivatives,” The Leading Edge, vol. 26, no. 12, pp. 1502–1505, 2007.

2. B. Verduzco, J. D. Fairhead, C. M. Green, and C. MacKenzie, “New insights into magnetic derivatives for structural mapping,” The Leading Edge, vol. 23, no. 2, pp. 116–119, 2004.

Regards

Avinash

Dear Mario Emilio Sigismondi Than you very much for your elaborated answer. And of course, I may need your help at times.

Regards and wishes

Yours sincerly

Dear Avinash Kumar Chouhan . Thank you. I found it very supportive.

Regards and Wishes