Index Table of contents Mapping Magnetic Basement from Aeromagnetic Data using AN-EUL Method A. Ben Salem 1 , S. Williams 1 , C. Green 1 , D. Fairhead 1,2 1 Getech, 2 University of Leeds Summary The AN-EUL method is based on the use of the derivatives of the magnetic field. It can provide information about the location and model type of isolated magnetic bodies. In this paper, we attempt to test the practical utility of the AN-EUL method in interpretation of aeromagnetic data over multiple magnetic sources. We have used the method to map the magnetic basement from magnetic data over complex basement structures. Generally, the method provides good solutions for mapping magnetic basement. These solutions were not necessarily obtained at the location of the total gradient peaks. Introduction A variety of semi-automatic methods, based on the use of derivatives of the magnetic anomalies, have been developed for the determination of causative source parameters such as locations of boundaries and depths. One of these techniques is the total gradient method, which was initially used in its complex function form and makes use of the Hilbert transform (Blakely, 1995). It does not require knowledge of magnetization direction and, therefore, it is useful in cases of remanent magnetization. In the total gradient method, it is typically assumed that the causative sources are 2D geologic structures such as contacts, dikes, and horizontal cylinders (MacLeod et al., 1993). For these models, depths can be obtained from the width of the total gradient anomalies (Roest et al., 1992) or based on ratio of the maxima of the total gradient to its higher derivatives if the source type is assumed (Thurston and Smith, 1997). However, correct estimate of the depth is obtained only when the source corresponds to the chosen model. Recently, Salem and Ravat (2003) presented the AN-EUL method to estimate both the location and nature of isolated magnetic sources using derivatives of Euler’s equation (Reid et al., 1990) into the total gradient of the magnetic field. Here, we have attempted to test the practical utility of the method to map magnetic basement from aeromagnetic data. AN-EUL Method The AN-EUL method is based on substituting derivatives of Euler’s equation (Reid et al., 1990) into the total gradient of the magnetic field to estimate simultaneously the source parameters generally sought from the Euler method (depth and structural index). In the AN-EUL method, the depth (z o ) and structural index are estimated at the location of the total gradient peaks as o o y y x x o AS AS AS AS AS z = =         - = , 2 1 0 2 0 1 [1] o o y y x x AS AS AS AS AS AS = =         - - = , 2 1 0 2 0 2 2 1 2 η , [2] where AS n is the total gradient of the n th -order derivative of the magnetic field M, defined as EGM 2007 International Workshop Innovation in EM, Grav and Mag Methods:a new Perspective for Exploration Capri, Italy, April 15 – 18, 2007