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We determined the relative mechanical strength of the Indian subcontinent by a robust coherence method based on multitaper spectral analysis on overlapping windows of equal size. Representing the elastic properties of the lithosphere by a transitional coherence wavelength, we bypass the need to input rheological variables such as Young''s modulus or Poisson''s ratio, which have been shown to vary on other continents. We compare our measurements in terms of age and find that regions underlain by Proterozoic basement are on average stronger than regions of Archaean age. This is in stark contrast to the common assumption that mechanical strength should increase progressively with time. This suggests they are indeed mechanically distinct, and that the transitional coherence wavelength adequately captures this distinction between regions of relative strength difference. Conversions of these values to absolute effective elastic thickness show a greater overlap, which is due to the many strong assumptions required in obtaining such absolute values and argues against their usage as a robust and well-constrained property of the elastic lithosphere. [Copyright &y& Elsevier]