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Automation of the SLUTH method: a novel approach to airborne magnetic data interpretationNormal access

Authors: J. Ulla, R. Smith, C. Samson and M. Vallée
Journal name: Near Surface Geophysics
Issue: Vol 8, No 6, December 2010 pp. 519 - 528
DOI: 10.3997/1873-0604.2010033
Special topic: Student-based Research
Language: English
Info: Article, PDF ( 3.92Mb )
Price: € 30

Summary:
A useful property of the anomalous magnetic field T associated with some simple geological bodies is that the field is homogeneous with respect to horizontal distance and height. Its horizontal and vertical derivatives are also homogeneous fields so the angle ratio θ of the lateral gradient over the vertical gradient is constant along rays emanating outward from a single point that represents the body location. Hence drawing these raypaths, which connect the same θ values at different upward continued heights along a profile, can be used to identify the location and depth of the source. This is the basis for the source location using the total-field homogeneity (SLUTH) method. A six-step procedure is proposed to automate the SLUTH method, allowing large amounts of data to be interpreted quickly and easily. Furthermore, the rate of decay of the field along these raypaths provides a means to estimate the type of body that is the cause of the anomaly. Once the type of body is known, a quantity related to the susceptibility can be estimated. An analysis of the results in the case when there is interaction between two proximal magnetic sheets shows a distortion when the bodies are within 600 m of each other. A similar distortion is seen when analysing field data from Timmins, Ontario, Canada, which consists of many other magnetic body models such as contacts and thin sheets. Adding noise to synthetic data shows that the estimates we obtain for the source parameters are robust for the typical noise levels seen in survey data. Because a lot of information about the characteristics of the causative geologic body can be determined using the method, it is a challenge to summarize the results on a single map. Our approach is to use different shaped symbols for each type of body, with the size of the symbol being proportional to the susceptibility-thickness and the shade indicative of the error in estimating the position. Data from Chibougamau, Quebec, Canada are used to illustrate these display techniques.


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