Discussion on `Spectral analysis of aeromagnetic data for geothermal energy investigation of Ikogosi Warm Spring - Ekiti State, southwestern Nigeria’

Abstract

Background: The recent paper by Abraham et al. (2014) 'Spectral analysis of aeromagnetic data for geothermal energy investigation of Ikogosi Warm Spring -Ekiti State, southwestern Nigeria' applied spectral analysis in the interpretation of aeromagnetic data for estimation of curie-point depths using a data window of 55 × 55 km; however, the employment of such small window may not be consistent with derived curie-point depth results. Discussion: Here, I would like to clarify and point out the possible errors in the paper.

Investigating heat and magnetic source depths in the Soutpansberg Basin, South Africa: exploring the Soutpansberg Basin Geothermal Field

“…The block sizes were chosen to ensure that spectral signatures across the approximate 7-km basin width were incorporated in the depth determinations. The use of multiple window sizes was to highlight the confidence in larger window sizes that would satisfy the condition of a curie point depth (CPD) that approximated L/2π (Nwankwo 2014). The 51-and 103-km window sizes were used to generate 36 and 14 data points, respectively, that enabled the production of depth contour maps.…”

“…The largest window size with L of 129 km and six data points ensured that spectral signatures were preserved. The authors, therefore, utilised three window sizes to verify discussions on the choice of window sizes that supported the use various and larger window sizes for the spectral analyses of data for depth determinations (Nwankwo 2014;Abraham et al 2014). The radially averaged power spectrum (RAPS) was generated from the transformed airborne magnetic data.…”

“…The energy was normalised by subtracting the log of the average spectral density (Oasis Geosoft Montaj 2014). (Shabalala et al 2015) In the computation of spectral energies, the data windows should have dimensions, L that ensure that the computed depths are within and more that the value of, L/2π to improve the depth resolution from spectral analysis (Nwankwo 2014). Abraham et al (2014), however, argued that dimensions of L ranging from 40,41,130,150, and 222 km have been applied to determine depths of 10, 15, 30, 32, and 46 km, respectively, on several case studies.…”