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Arabian Journal of Geosciences

, Volume 7, Issue 7, pp 2749–2759 | Cite as

2D inversion of the magnetotelluric data from Mahallat geothermal field in Iran using finite element approach

  • Behrooz Oskooi
  • Mehrdad Darijani
Original Paper

Abstract

The natural-field magnetotelluric (MT) method has proven very useful for mapping the geothermal fields as resistivity sections. The depth of investigation of the MT method is sufficiently large to penetrate deep into the upper crust. MT soundings along two transects across Mahallat geothermal field in Iran were carried out to determine the crustal structure in the region. The selected MT profiles in the region cross over the hydrothermally altered zones and different geological structures. Data were acquired along two profiles crossing the Mahallat hot springs with a total of 28 MT stations in a frequency range of 8,000 to 0.008 Hz. Spacing between stations was kept 500 m for a good resolution. We have used the code MT2DInvMATLAB for inversion using the method of finite elements for forward modeling. Apparent resistivity and phase data of transverse electric (TE), transverse magnetic (TM), and TE + TM modes along each profile were modeled. The geothermal fluid reservoir is resolved at 1,000 to 3,000 m depth and the geothermal resource is estimated to be located at 7,000 m or deeper.

Keywords

Electrical resistivity Geothermal Interpretation Magnetotelluric Mahallat 2D inversion 

Notes

Acknowledgments

The research council of the University of Tehran (UT) is acknowledged for the financial support of the first author’s sabbatical leave at Uppsala University (UU) in the period of October 2011 to October 2012. The Department of the Earth Sciences of UU is also appreciated for hosting the first author as guest researcher. We would like to thank Dr. M. Mirzaei from Arak University in Iran for the financial support of the field work and also Dr. M. Montahaee for her useful guidance on the data processing.

References

  1. Bahr K (1988) Interpretation of the magnetotelluric impedance tensor: regional induction and local telluric distortion. J Geophys 62:119–127Google Scholar
  2. Bahr K (1991) Geological noise in magnetotelluric data—a classification of distortion types. Phys Earth Planet Inter 66(1–2):24–38CrossRefGoogle Scholar
  3. Berktold A (1983) Electromagnetic studies in geothermal regions. Geophys Surv 6:173–200CrossRefGoogle Scholar
  4. Caldwell T, Bibby H, Brown C (2004) The magnetotelluric phase tensor. Geophys J Int 158:457–469CrossRefGoogle Scholar
  5. Dhanunjaya Naidu G, Manoj C, Patro P, Sreedhar S, Harinarayana T (2011) Deep electrical signatures across the Achankovil shear zone, Southern Granulite Terrain inferred from magnetotellurics. Gondwana Res 577:367–389Google Scholar
  6. Johnston J, Pellerin L, Hohmann G (1992) Evaluation of electromagnetic methods for geothermal reservoir detection. Geotherm Resour Counc Trans 16:241–245Google Scholar
  7. Jones A, Dumas I (1993) Electromagnetic images of a volcanic zone. Phys Earth Planet Interiors 81:289–314CrossRefGoogle Scholar
  8. Lee S, Kim J, Song Y, Lee C (2009) MT2DInvMatlab—a program in MATLAB and FORTRAN for two-dimensional magnetotelluric inversion. Comput Geosci 35:1722–1734CrossRefGoogle Scholar
  9. Loke M (2000) Topographic modeling in electrical imaging inversion. 62nd Meeting of the European Association of Exploration Geoscientists, Glasgow, Scotland, pp. 1–4Google Scholar
  10. Mehanee S, Zhdanov M (2002) Two-dimensional magnetotelluric inversion of blocky geoelectrical structures. J Geophys Res 107:EPM 2-1–EPM 2-11Google Scholar
  11. Montahaie M, Brasse H, Oskooi B (2010) Crustal conductivity structure of a continental margin, from magnetotelluric investigations. J Earth Space Phys 36(2):21–32Google Scholar
  12. Oskooi B, Pedersen L, Smirnov M, Arnason K, Eysteinsson H, Manzella A (2005) The deep geothermal structure of the Mid-Atlantic Ridge deduced from MT data in SW Iceland. Phys Earth Planet Inter 150:183–195CrossRefGoogle Scholar
  13. Patro P, Sarma S (2009) Lithospheric electrical imaging of the Deccan trap covered region of western India. J Geophys Res 114:B01102Google Scholar
  14. Rodi W (1976) A technique for improving the accuracy of finite element solutions for magnetotelluric data. Geophys J Roy Astron Soc 44:483–506CrossRefGoogle Scholar
  15. Roy K, Dey S, Srivastava S, Biswas S (2004) What to trust in a magnetotellyric model. Geophys J Int 8(2):157–17Google Scholar
  16. Siripunvaraporn W, Egbert G (2000) An efficient data-subspace inversion method for 2-D magnetotelluric data. Geophysics 65:791–803CrossRefGoogle Scholar
  17. Smirnov M (2003) Magnetotelluric data processing with a robust statistical procedure having a high breakdown point. Geophys J Int 152:1–7CrossRefGoogle Scholar
  18. Smirnov M, Pedersen L (2009) Magnetotelluric measurements across the Sorgenfrei–Tornquist Zone in southern Sweden and Denmark. Geophys J Int 176:443–456CrossRefGoogle Scholar
  19. Swift C (1967) A magnetotelluric investigation of an electrical conductivity anomaly in the south-western United States, PhD thesis. M.I.T., Cambridge, MA, USAGoogle Scholar
  20. Tikhonov A, Arsenin V (1977) Solution of ill-posed problems. Wiley, New York, 258Google Scholar
  21. Unsworth M (2010) Magnetotelluric studies of active continent–continent collisions. Surv Geophys 31:137–161. doi: 10.1007/s10712-009-9086-y CrossRefGoogle Scholar
  22. Ushijima K, Mustopa E, Jotaki H, Mizunaga H (2005) Magnetotelluric soundings in the Takigami geothermal Aria, Japan. Proc. World Geothermal Congress, AntaliaGoogle Scholar
  23. Yi M, Kim J, Chung S (2003) Enhancing the resolving power of least-squares inversion with active constraint balancing. Geophysics 68:931–941CrossRefGoogle Scholar

Copyright information

© Saudi Society for Geosciences 2013

Authors and Affiliations

  1. 1.Institute of GeophysicsUniversity of TehranTehranIran

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