Performance evaluation of spectral analysis and Werner deconvolution interpretation techniques in magnetic method

• Spectral methods are appropriate for thin bodies in determining depth (error < 5%). if spectral method is applied for dike like bodies, the error is considerable. in the case of fault model, the bottom depth (H2) determined from filtered spectrum gives less percent error (< 15%).
• The error in depth determined for sheet from magnetic anomaly by Werner method is zero. This shows the efficacy of the Werner method for sheet like models.
• The percent error in depth is almost zero (Figure 9(b)) for w/h greater than two when determined from horizontal gradient. The percent error in half-width is almost zero (Figure 10) for W/H > 2.
• This exponential decrease is more pronounced for deeper faults and < 10% for H2/H1 values > 3. For deeper sources of vertical fault, the depth (H1) obtained from horizontal gradient anomaly is preferred than the depth obtained from the magnetic anomaly.
• It has been observed that Werner deconvolution technique yields reasonable values in depth for thin sources and also width in the case of dyke. The spectral methods are more useful for extracting the long wavelength anomalies (by filtering) due to deeper sources.

Determining the depth of anomalous geological subsurface structure is an important parameter in any of geophysical 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. Werner 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 performance 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.