INTERPRETATION OF MAGNETIC DATA BASED ON TILT DERIVATIVE METHODS AND ENHANCEMENT OF TOTAL HORIZONTAL GRADIENT, A CASE STUDY: ZANJAN DEPRESSION

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SHAHVERDI M.; NAMAKI L.; MONTAHAEI M.; MESBAHI F.; BASAVAND M.

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Journal: Journal of the Earth and Space Physics Year:2017 | Volume:43 | Issue:1 Page(s): 101-113

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Title

INTERPRETATION OF MAGNETIC DATA BASED ON TILT DERIVATIVE METHODS AND ENHANCEMENT OF TOTAL HORIZONTAL GRADIENT, A CASE STUDY: ZANJAN DEPRESSION

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Keywords

POTENTIAL FIELDQ2

MAGNETIC ANOMALYQ2

TILT ANGLEQ1

HORIZONTAL GRADIENTQ3

VERTICAL GRADIENTQ1

EDGE DETECTIONQ1

Abstract

Magnetic survey data are generally used to map faults, geologic contacts and magnetic ore bodies. The spatial distribution of magnetic sources is usually determined during the mapping process. Variation in depth, magnetization and geometrical parameters generate MAGNETIC ANOMALY waveform. Direction of the remanent and induced magnetization vector also affect the shape of these waveform. A MAGNETIC ANOMALY waveform, includes amplitude, phase and wavelength. Putting these parameters altogether makes the interpretation of the magnetic data a difficult task. There are different useful methods for interpretation of a magnetic map. Generally, these methods are based on reduction of data to a simpler form, so that the edges and center of the causative bodies are determined easily. In the recent years many methods have been used to balance the difference between various anomaly amplitudes. Each method is designed to determine a specific parameter of the magnetic anomalies. Using local phase filters are being common in POTENTIAL FIELD data interpretation. They are high-pass filters based on horizontal and vertical derivatives, such as total horizontal derivative, TILT ANGLE, theta map, etc. EDGE DETECTION of a magnetic structure is one of the most important task in the interpretation of magnetic data. For this purpose, in this research we have used two local phase filters: TILT ANGLE (TDR) and Total Gradient of TILT ANGLE (TAHG). As stated, TILT ANGLE filter is used in determining the boundary of source anomaly. It is relatively less sensitive to the depth of the source, so, it can resolve shallow and deep sources as well. As tilt derivative is a function of the ratio of the vertical and horizontal derivatives of field intensity, it does not contain information on the strength of the geomagnetic field nor the susceptibility of the causative bodies. The peaks of TILT ANGLE amplitude should be located over the center and its zeros over the edges of the source body. It strongly depends on the inclination of magnetic field. Another enhanced method we have used in this study for determining the boundaries of the structures is the HORIZONTAL GRADIENT of TILT ANGLE (the TAHG). It is defined by taking the arctangent of the vertical derivative of the HORIZONTAL GRADIENT, divided by the modulus of the HORIZONTAL GRADIENT. TAHG equalizes the signals obtained from the shallow and deep sources. Its notable features are that it produces amplitude maxima over the source's edges, gives suitable resolution and is less dependent on the depth of structures. Like the TDR, this method depends on the inclination of magnetic field. We applied these methods for synthetic noise-free and noisy data. Preparing the total magnetic responses of synthetic models as well as EDGE DETECTION calculations have all been done in MATLAB. In comparison with common methods like HORIZONTAL GRADIENT and analytic signal, it delineates the edges of source bodies more efficiently and accurately. Furthermore the TAHG method has better resolution in determining the boundaries of deeper sources than the TDR method. We applied the stated algorithm, on real data. The aeromagnetic dataset from Zanjan region was selected to be used in the TAHG method. The Zanjan depression is a narrow and continuous igneous basin, located in the north western Zanjan province. There are many young active and basement faults in the study area. Total MAGNETIC ANOMALY map of the region, shows two major structural trends in NW-SE and NE-SW, respectively. By applying the two different EDGE DETECTION algorithms we obtained the hidden boundaries of the basement which is not detectable in the geological maps because of the thick sedimentary covers. The results show that TAHG method is suitable for determining the basement faults and boundaries, as well as mapping the contacts of magnetic units.

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APA: Copy

SHAHVERDI, M., NAMAKI, L., MONTAHAEI, M., MESBAHI, F., & BASAVAND, M.. (2017). INTERPRETATION OF MAGNETIC DATA BASED ON TILT DERIVATIVE METHODS AND ENHANCEMENT OF TOTAL HORIZONTAL GRADIENT, A CASE STUDY: ZANJAN DEPRESSION. JOURNAL OF THE EARTH AND SPACE PHYSICS, 43(1 ), 101-113. SID. https://sid.ir/paper/80380/en

Vancouver: Copy

SHAHVERDI M., NAMAKI L., MONTAHAEI M., MESBAHI F., BASAVAND M.. INTERPRETATION OF MAGNETIC DATA BASED ON TILT DERIVATIVE METHODS AND ENHANCEMENT OF TOTAL HORIZONTAL GRADIENT, A CASE STUDY: ZANJAN DEPRESSION. JOURNAL OF THE EARTH AND SPACE PHYSICS[Internet]. 2017;43(1 ):101-113. Available from: https://sid.ir/paper/80380/en

IEEE: Copy

M. SHAHVERDI, L. NAMAKI, M. MONTAHAEI, F. MESBAHI, and M. BASAVAND, “INTERPRETATION OF MAGNETIC DATA BASED ON TILT DERIVATIVE METHODS AND ENHANCEMENT OF TOTAL HORIZONTAL GRADIENT, A CASE STUDY: ZANJAN DEPRESSION,” JOURNAL OF THE EARTH AND SPACE PHYSICS, vol. 43, no. 1 , pp. 101–113, 2017, [Online]. Available: https://sid.ir/paper/80380/en

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