Local-Regional Decomposition of the Telluric Tensor

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Abstract

The article considers the possibilities of using the telluric tensor in magnetotellurics, determined from the linear relations of the electric field at the ordinary and base points. Particular attention is paid to the local-regional decomposition of the telluric tensor, allowing to separate the influence of near-surface inhomogeneities and the studied deep structures. Approaches that are widely used in the analysis of the impedance tensor are adapted by the authors for the analysis of the telluric tensor and tested on synthetic data calculated for a three-dimensional model with a deep conductive structure and an inhomogeneous near-surface layer. A phase tensor determined from the telluric tensor and free from near-surface effects is considered. It is shown that maps of invariant parameters and polar diagrams make it possible to estimate the dimensions of the medium, localize deep structures and estimate their extension.

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About the authors

М. А. Sukonkin

Lomonosov Moscow State University

Author for correspondence.
Email: msukonkin@mail.ru
Russian Federation, Moscow

P. Yu. Pushkarev

Lomonosov Moscow State University

Email: pavel_pushkarev@list.ru
Russian Federation, Moscow

References

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Supplementary files

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2. Fig. 1. Geoelectric model. Top - section along the central meridional profile. At the bottom - map of the upper layer containing PPN (size 22.5 × 22.5 km). The background UES of the layer is 10 Ohm ∙ m, the UES of the BCP varies from 1 to 100 Ohm ∙ m. The yellow rectangle is the position of the deep graben. The circles are rounded points, the data of which are presented in the following figures.

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3. Fig. 2. Moduli curves of the principal components of the telluric tensor Txx and Tyy (a), (c) and their phases (b), (d). At the top (a), (b) - point 1 above the isometric PPN, at the bottom (c), (d) - point 2 above the elongated PPN.

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4. Fig. 3. Moduli curves of the additional components of the telluric tensor Txy and Tyx (a), (c) and their phases (b), (d). At the top (a), (b) - point 1 above the isometric PPN, at the bottom (c), (d) - point 2 above the elongated PPN.

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5. Fig. 4. Phase tensor component curves at points 1 (left) and 2 (right).

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6. Fig. 5. Maps of the effective component modulus Tef, period 10 s: (a) - model without RCP; (b) - with RCP. The black dashed line indicates the boundaries of the graben.

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7. Fig. 6. Phase maps of the effective Tef component, period of 10 s: (a) - model without RCP; (b) - with RCP. The black dashed line indicates the boundaries of the graben.

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8. Fig. 7. Maps of the Swift skewTS asymmetry parameter, period 10 s: (a) - model without RCP; (b) - with RCP. The black dashed line indicates the boundaries of the graben.

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9. Fig. 8. Maps of the Bar skewTB asymmetry parameter, period 10 s: (a) - model without RCP; (b) - with RCP. The black dashed line indicates the boundaries of the graben.

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10. Fig. 9. Map of the azimuthal angle αT (shown with a cross together with αT + 90°) against the background of the modulus values of the parameter βT, period 10 s.

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11. Fig. 10. Polar diagrams of the component moduli [T] at point 1 at periods of 1 and 10 s (from left to right) for the model variants without (top) and with (bottom) TCP. Black colour - |Txx| component, red - |Txy|.

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12. Fig. 11. Polar diagrams of the moduli of the components [T] at point 2 at periods 1 and 10 s (from left to right) for the model variants without (top) and with (bottom) TCP. Black colour - |Txx| component, red - |Txy|.

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13. Fig. 12. Polar plots of the phase of the principal component arg (Txx) at periods 1 and 10 s (from left to right) at point 1 (top) and point 2 (bottom), black dashed line - model without BCP, red - with BCP.

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14. Fig. 13. Polar diagrams of the telluric phase tensor at periods 1 and 10 s (from left to right) at point 1 (top) and point 2 (bottom). The black and red lines are the principal and additional components for the model with PPN, the purple and blue dashed lines are the same for the model without PPN. Black and blue arrows show (with 90° accuracy) the α and α - β directions.

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