Abstract
The coast effect on magnetotelluric (MT) data over South India has been studied using 2D Forward modelling. The peninsular shape of Indian shield is bounded by the Arabian Sea in the west, the Indian Ocean in the south and the Bay of Bengal in the east. The distance between Arabian Sea and Bay of Bengal varies from ‘0’ in the south to 1200 km near 19°N Latitude which passes through Mumbai. This region is close to sea, which can cause a distortion in the MT parameters of apparent resistivity and phase. MT covers a wide frequency range (10+4 to 10−4 Hz), which enables us to image the resistivity of subsurface layers from few hundred meters to as deep as few hundreds of km. MT results in the TE and TM mode show significantly different behavior when the subsurface is non-one dimensional. Due to coast, in general apparent resistivity increases as period increases in TM-mode, while apparent reistivity decreases with increasing period in TE mode. Near the coastal sites (5, 30 km) magnetotelluric data gets distorted due to coast effect when the period is more than 0.1 s. Coast effect depends on Land distance, Land Resistivity and depth to the top of the conducting asthenosphere. If land distance is more coast effect is less, resistivity is more coast effect is more and if depth of conductor is small coast effect is more. Our numerical study on coast effect quantifies the effect on MT responses and discusses the necessity of including coast in the models while modeling with the field data. The field data obtained along 240 km long profile in Dharwar region has been inverted by considering TE, TM and TE & TM modes. On the basis of these results, it can be concluded that the resistivity model obtained from TE-mode is closer to the actual model as compared to TM-mode.
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References
Bailey RC (1977) Electromagnetic induction over the edge of a perfectly conducting ocean. Geophys J R Astron Soc 48:276–287
Brewitt-Taylor CR, Weaver JT (1976) On the finite difference solution of two-dimensional induction problems. Geophys J R Astron Soc 47:375–396
Dosso HW, Meng ZW (1992) The coast effect response in geomagnetic field measurements. Phys Earth Planet Inter 70:39–56
Durrheim RJ, Mooney WD (1994) Evolution of the Precambrian lithosphere: seismological and geochemical constraints. J Geophys Res 99:15359–15374
Fischer G, Schnegg P-A, Usadel K (1978) Electromagnetic response of an ocean-coast model to E-polarization induction. Geophys J R Astron Soc 53:599–618
Fischer G, Schnegg PA, Usadel KD (1980) Electromagnetic induction at a model ocean coast. J Geomagn Geoelectr 32:67–71
Gokarn SG, Gupta G, Rao CK (2004) Geoelectric structure of the Dharwar Craton from magnetotelluric studies: Archean suture identified along the Chitradurga–Gadag schist belt. Geophys J Int 158:712–728
Gupta S, Rai SS, Prakasam KS, Srinagesh D, Chadha RK, Priestly K, Gaur VK (2003) First evidence for anomalous thick crust beneath mid-Archean western Dharwar craton. Curr Sci 84:1219–1226
Jones FW, Pascoe JL (1972) The perturbation of alternating geomagnetic fields by three-dimensional conductivity inhomogeneities. Geophys J R Astron Soc 27:479–485
Karmalkar NR, Duraiswami RA, Chalapathi Rao NV, Paul DK (2009) Mantle-derived mafic-ultramafic xenoliths and the nature of Indian sub-continental lithosphere. J Geol Soc India 73:657–679
Key K, Constable S (2011) Coast effect distortion of marine magnetotelluric data: insights from a pilot study offshore northeastern Japan. Phys Earth Planet Inter 184:194–207
Lilley FEM, Arora BR (1982) The sign convention for quadrature Parkinson arrows in geomagnetic induction studies. Rev Geophys Space Phys 20:513–518
Monteiro Santos FA, Nolasco M, Almeida EP, Pous J, Mendes-Victor LA (2001) Coast effect on magnetic and magnetotelluric transfer functions and their correction: application to MT soundings carried out in SW Iberia. Earth Planet Sci Lett 186:283–295
Naidu GD, Manoj C, Patro PK, Sreejesh V, Sreedhar, Harinarayana T (2011) Deep electrical signatures across the Achankovil Shear Zone, Southern Granulite Terrain inferred from magnetotellurics. Gondwana Res. doi:10.1016/j.gr.2010.12.002
Nicoll MA, Weaver JT (1977) H-polarization induction over an ocean edge coupled to the mantle by a conducting crust. Geophys J R Astron Soc 49:427–442
Pandey D, Sinha M, MacGregor L, Singh S (2008) Ocean coast effect on magnetotelluric data: a case study from Kachchh, India. Mar Geophys Res 29:185–193
Parkinson W (1959) Directions of rapid geomagnetic fluctuations. Geophys J R Astron Soc 2(1):1–14
Patro PK, Sarma SVS (2009) Lithospheric electrical imaging of the Deccan trap covered region of western India. J Geophys Res 114:1–16
Raval U, Veeraswamy K (2000) The radial and linear modes of interaction between mantle plume and continental lithosphere: a case study from western India. J Geol Soc India 56:525–536
Raval U, Weaver J, Dawson T (1981) The ocean-coast effect reexamined. Geophys J R Astron Soc 67:115–123
Rikitake T (1959) Anomaly of geomagnetic variations in Japan. Geophys J R Astron Soc 2:276–287
Rodi W, Mackie RL (2001) Nonlinear conjugate gradients algorithm for 2D magnetotelluric inversions. Geophysics 66:174–187
Singh UK, Yash K, Ramesh SP (1995) Effect of coast on magnetotelluric measurements in India. Ann Geofis XXXVIII(3–4):331–335
Storey BC (1995) The role of mantle plumes in continental breakups: case histories from Gondwanaland. Nature 377:301–308
Thakur NK, Mahashabde MV, Atom BR, Singh BP, Srivsataus BJ, Prasad SN (1981) Anomalies in geomagnetic variations on peninsular India near Palk Strait. Geophys Res Lett 8:947–950
Veeraswamy K (1993) Quantitative demarcation of coast-effect over Saurashtra peninsula. In: Proceedings of IGU seminar on perspectives and prospects in geosciences towards the new industrial policy, pp 130–140
Wannamaker PE, Stodt JA, Rijo L (1986) Two-dimensional topographic response in magnetotellurics modeled using finite elements. Geophysics 51:2131–2144
Weaver JT, Agarwal AK (1991) Is addition of induction vectors meaningful? Phys Earth Planet Inter 65:267–275
Yang J, Lee ChK, Min DJ, Lee H, Lee TJ (2012) 1-D Crustal resistivity structure revealed by sea effect corrected magnetotelluric (MT) data obtained at Jeju Island, Korea. J Appl Geophys 76:92–101
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The authors are thankful to Director, CSIR-NGRI for his kind permission to publish this work. We are thankful to the reviewers for their valuable comments and suggestions, which have improved the quality of this paper.
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Malleswari, D., Veeraswamy, K. Numerical simulation of coast effect on magnetotelluric measurements. Acta Geod Geophys 49, 17–35 (2014). https://doi.org/10.1007/s40328-013-0039-z
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DOI: https://doi.org/10.1007/s40328-013-0039-z