Performance evaluation of spectral analysis and Werner deconvolution interpretation techniques in magnetic method Subrahmanyam M. a, ⁎, Fekadu Tamiru Gebissa b a Department of Geophysics, Andhra University, Visakhapatnam 530003, India b Department of Earth Sciences, Wollega University, Naqamte, Ethiopia abstract article info Article history: Received 19 March 2016 Received in revised form 5 January 2017 Accepted 13 January 2017 Available online 19 January 2017 Determining the depth of anomalous geological subsurface structure is an important parameter in any of geo- physical methods. Though, numerous magnetic interpretation techniques are available in literature for locating depth to the causative source, no specific information is found on the performance of any of the techniques. Wer- ner deconvolution and Spectral methods are widely used to determine the approximate depth to the causative sources, which are then used in modeling methods. An attempt has been made in this study to evaluate the per- formance of Werner and spectral methods. Synthetic magnetic anomalies are generated over sheet, dyke and fault models for different combinations of geometric dimensions of the bodies and magnetization angles. These anomalies were interpreted with the two methods: Werner deconvolution and Spectral analysis. The error percentages are calculated as the difference between the theoretical and interpreted values. In addition, the results are discussed for their performance. It is observed that Werner method yields more reasonable values for depth compared to spectral methods particularly when body widths are more and deep seated or faulting is deep. In case of dyke model, the Werner method determines width also reliably. © 2017 Elsevier B.V. All rights reserved. Keywords: Werner deconvolution Spectral analysis Depth Percent error Performance 1. Introduction The purpose of magnetic surveying is to investigate the anomalous subsurface geological features causing variations in the observed mag- netic field. These magnetic field variations arise due to the differences in the magnetic properties of the underlying rocks. Many magnetic interpretation methods have been developed to determine the depth of the geologic structure of different geometric shapes. The methods are based on: i) graphical techniques using a few characteristic points on the magnetic profile (Koulomzine et al., 1970; Am, 1972; Subrahmanyam and Prakasa Rao, 2009) ii) nomograms (Prakasa Rao et al., 1986) iii) spectral analysis techniques (Bhattacharya, 1971; Bhattacharya and Leu, 1975; Sengupta and Das, 1975; Bhimasankaram et al., 1978), and iv) numerical techniques such as Werner deconvolution method (Hartman et al., 1971; Ku and Sharp, 1983), Euler deconvolution method (Thompson, 1982; Reid et al., 1990), and least-squares minimization approaches (McGrath and Hood, 1973; Silva, 1989; Dondurur and Pamukcu, 2003). The large potential field data demands automatic interpretation techniques such as Euler method (Thompson, 1982) and Werner deconvolution (Werner, 1953). The Euler's interpretation technique is popular method of interpretation in magnetic data because it requires no information about the magnetization vector and only a little a priori knowledge about the magnetic source geometry (Barbosa et al., 2000). The Euler equation is solved in a nonlinear fashion using optimization technique (Dewangan et al., 2007). However, most of the approaches to nonlinear least-squares inverse problem rely on good initial esti- mates of the model parameters. Euler deconvolution has come into wide use as an aid to interpret profile or gridded magnetic survey data. Thompson (1982) further studied and implemented the method by applying Euler deconvolution to synthetic and real magnetic data along profiles. This method is used for rapid interpretation of potential field data and it belongs to automatic depth estimate methods which is designed to provide computer-assisted analysis on large volumes of magnetic and gravity data. Estimation of the depth of magnetic source using different methods is preferably applied to profiles of large magnetic data sets. Kearey (2002) addressed that the interpretation of individual profiles is preferable for most geophysicists because they show fine sampling in- tervals, which generally lead to good understanding of the geology. There is no single method giving a unique solution for estimating the ac- curate depth because of the inherent ambiguity due to complex subsur- face structures. There is no systematic performance evaluation except a few (Am, 1972; Prakasa Rao and Subtahmanyam, 1985; Subrahmanyam et al., 2013) for most of the methods. The professional geoscientist is at confusion as to which method among the many available would be Journal of Applied Geophysics 138 (2017) 102–113 ⁎ Corresponding author. E-mail addresses: smangalampalli@rediffmail.com (S. M.), fekadugebissa@gmail.com (F.T. Gebissa). http://dx.doi.org/10.1016/j.jappgeo.2017.01.017 0926-9851/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Applied Geophysics journal homepage: www.elsevier.com/locate/jappgeo