1887
Advances in Electromagnetic, Gravity and Magnetic Methods for Exploration
  • E-ISSN: 1365-2478

Abstract

ABSTRACT

Downward continuation is a useful transformation, mainly used to enhance measured gravity or magnetic field anomalies. It is known to be an unstable transformation that should be strictly used only in the harmonic region, apparently preventing any meaningful application to continuations inside the source volume. Despite these well‐known theoretical and practical limitations it has been used to recover source parameters by different methods, here referred to as normalized full gradient methods. Such methods show that downward continuation may be extended to the source volume, which is assumed to contain one‐point, isolated singularities, which is a quasi‐harmonic region. We modify the normalized full gradient method focusing our attention to the way the downward continuation is normalized. Differently from normalized full gradient methods, we study the effect of the normalization not only on the analytical signal modulus of the downward continued field but also on the downward continuation of the gravity or magnetic fields themselves. With our method, called normalized downward continuation, several statistically meaningful normalizations are considered, some of them yielding improved, more resolved depth estimations for synthetic as well as measured total‐field anomalies. From a statistical point of view, the downward continued field tends to have right‐skewed histograms at shallow depths, while becoming symmetrically distributed at greater depths. This occurs because, as the depth of continuation increases, the intrinsic error propagation of the downward continuation allows the error to dominate with respect to the source‐related signal. For non‐isolated anomalies, consistent results are also obtained but the normalizing factors must be computed within windows centred to the studied anomaly.

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2011-09-14
2020-04-04
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References

  1. AydinA.2007. Interpretation of gravity anomalies with the normalized full gradient (NFG) method and an example. Pure and Applied Geophysics164, 2329–2344.
    [Google Scholar]
  2. BerezkinV.M.1967. Application of the total vertical gradient of gravity for determination of the depth to the sources of gravity anomalies. Razvedochnaya Geofizika (Exploration Ggeophysics) 18, 69–79 (in Russian).
    [Google Scholar]
  3. BerezkinV.M.1988. Method of the Total Gradient in Geophysical Prospecting . Nedra (in Russian).
    [Google Scholar]
  4. CianciaraB. and MarcakH.1979. Geophysical anomaly interpretation of potential fields by means of singular points method and filtering. Geophysical Prospecting27, 251–260.
    [Google Scholar]
  5. DondururD.2005. Depth estimates for Slingram electromagnetic anomalies from dipping sheet‐like bodies by the normalized full gradient method. Pure and Applied Geophysics162, 2179–2195.
    [Google Scholar]
  6. ElysseievaI.S.1975. Estimation of density boundaries by means of the total normalized gradient method with variable normalization. Razvedochnaya Geofizika (Exploration Ggeophysics)69, 102–108 (in Russian).
    [Google Scholar]
  7. ElysseievaI.S., BerezkinV.M. and EgorovaI.P.1972. Application of the Filon method for spectral decomposition at use of total normalized gradient GH(x,z). Prikladnaya Geofizika (Applied Geophysics)67, 139–145 (in Russian).
    [Google Scholar]
  8. ElysseievaI.S. and PastekaR.2009. Direct interpretation of 2D potential fields for deep structures by means of the quasi‐singular points method. Geophysical Prospecting57, 683–705.
    [Google Scholar]
  9. FediM.2007. DEXP: A fast method to determine the depth and the structural index of potential fields sources. Geophysics72, I1–I11.
    [Google Scholar]
  10. FediM. and FlorioG.2002. A stable downward continuation by using ISVD method. Geophysical Journal International151, 146–156.
    [Google Scholar]
  11. FediM., FlorioG. and QuartaT.2009. Multiridge analysis of potential fields: Geometrical method and reduced Euler deconvolution. Geophysics74, L53–L65.
    [Google Scholar]
  12. FlorioG. and FediM.2006. Euler deconvolution of vertical profiles of potential field data. 76th SEG meeting, New Orleans , Louisiana , USA , Expanded Abstracts, 958–962.
  13. FlorioG., FediM. and RapollaA.2009. Interpretation of regional aeromagnetic data by multiscale methods: The case of Southern Apennines (Italy). Geophysical Prospecting57, 479–489.
    [Google Scholar]
  14. GerovskaD., StavrevP. and Arauzo‐BravoM.J.2005. Finite‐difference Euler deconvolution algorithm applied to the interpretation of magnetic data from Northern Bulgaria. Pure and Applied Geophysics162, 591–608.
    [Google Scholar]
  15. KuC., TelfordW. and LimS.1971. The use of linear filtering in gravity problems. Geophysics36, 1174–1203.
    [Google Scholar]
  16. NabighianM.N.1974. Additional comments on the analytic signal of two‐dimensional magnetic bodies with polygonal cross‐section. Geophysics39, 85–92.
    [Google Scholar]
  17. ParkerR.L.1977. Understanding inverse theory. Annual Review of Earth and Planetary Sciences5, 35–64.
    [Google Scholar]
  18. RoyA.1967. Convergence in downward continuation for some simple geometries. Geophysics32, 853–866.
    [Google Scholar]
  19. SailhacP. and GibertD.2003. Identification of sources of potential fields with the continuous wavelet transform: 2‐D wavelets and multipolar approximations. Journal of Geophysical Research108, 2262.
    [Google Scholar]
  20. SalemA.2005. Interpretation of magnetic data using analytic signal derivatives. Geophysical Prospecting53, 75–82.
    [Google Scholar]
  21. SalemA. and RavatD.2003. A combined analytic signal and Euler method (AN‐EUL) for automatic interpretation of magnetic data. Geophysics68, 1952–1961.
    [Google Scholar]
  22. SindirgiP., PamukcuO. and OzyalinS.2008. Application of normalized full gradient method to self potential (SP) data. Pure and Applied Geophysics165, 409–427.
    [Google Scholar]
  23. ZengH., MengX., YaoC., LiX., LouH., GuangZ. and LiZ.2002. Detection of reservoirs from normalized full gradient of gravity anomalies and its application to Shengli oil field, east China. Geophysics67, 1138–1147.
    [Google Scholar]
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  • Article Type: Research Article
Keyword(s): Downward continuation , Harmonic region and Normalized full gradient
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