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A first order estimate of Curie depth and lithospheric thickness variation beneath the Indian region has been obtained using the available geothermic data. The Curie depth is found to vary from 18 to 68 km and the lithospheric thickness from 38 to 186 km. These estimates conform well with the MAGSAT and seismological findings. Both the parameters exhibit covariancy and suggest the possibility of approximating heat flow values and lithospheric thickness in geothermally uncharted areas using Curie point geotherm depths derived from airlsatellite-borne magnetic anomalies. Interestingly, the areas with shallow Curie depth and lithospheric thickness are found to be associated with a thin crust, higher heat flow, higher geothermal gradients and positive gravity anomalies, and vice versa. Large thickness estimate of magnetic crustal layer, extending below the Moho, demands a new conceptual understanding. The study has brought out a good case for wider use of magneto-thermometry and provides understanding of the geodynamic evolution of the Indian subcontinent.

The estimation of thickness of trap rocks in the earthquake‐affected Koyna area is an important parameter for revealing the topography that existed before the Deccan volcanism. In the present work, a case history is presented delineating a three‐dimensional block model for the Koyna area by the spectral analysis of aeromagnetic data. The thickness in the area was found to vary from 700 to 2200 m, which correlates well with the results of other geophysical investigations.

To understand the phenomenon of frequent reversals of axial geocentric dipole fields it is essential to understand the spectral structure of geomagnetic reversal series and search for possible exogenetic (cosmic) factors associated with its dynamic behaviour. A scheme of Walsh spectrum analysis (which is more efficient and appropriate for binary processes as compared to Fourier Spectrum Analysis and Maximum Entropy Method), has been applied, for the first time, to the available world‐wide paleomagnetic measurements during phanerozoic (last 570 million years). The results postulate long‐term cyclicity in magnetic stratigraphy with reversal periods of 285, 114, 64, 47 and 34 million years with distinct resolution. The similar analysis was further repeated by dividing the total record in two sub‐series. These results indicate mean periods of 71, 47 and 32‐ m.y. These peaks are statistically significant at 90% confidence level. These results, thus, question the widely accepted theory of randomness of geomagnetic reversal for long‐period sequence. Surprisingly, the maximum spectral power is found for the Cosmic year (285 m.y.) Term (period of complete revolution of solar system around the Milky way galactic centre). The other reversal periods correspond nicely with the solar system's periods of galactocentric radial motion, interaction of spiral density wave with galactic orbit and solar oscillation in and outside of orbital plane. Such a remarkable correlation and harmony between observed gravitational phenomena and terrestrial records of electromagnetic processes on the cosmic scale appear to be of fundamental importance in macroscopic physics.

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