MAPPING OF CRUSTAL DISCONTINUITIES BY WAVELENGTH FILTERING OF THE GRAVITY FIELD1

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Abstract
A statistical technique, based on the concept of a 1D energy density spectrum of the observed gravity field, has been used to compute ensemble average depths to various horizons containing causative sources of random geometric shape, size, density, etc. The plot of the logarithm of the energy of the observed Bouguer anomaly versus the angular frequency can be approximated, over a certain frequency band, by a linear segment whose slope is related to an average ensemble depth around which a random distribution of numerous anomalous sources exists. Suitable matched filters, based on the computed values of intercepts and slopes of several linear segments approximating the spectrum, have been used to deconvolve the gravity effects associated with the causative sources, occurring around their respective mean depths. The individual deconvolved gravity effects thus separated out have been modelled using the sinx/xmethod by assuming a fluctuating interface between two formations.The applicability of the present method has been assessed using two observed Bouguer anomaly profiles: one from Ujjain to Mahan, and the other from Jhansi to Mandla where Deep Seismic Sounding (DSS) results are available. The proposed geological crustal models along these two profiles exhibit reasonably good agreement with those obtained from DSS results. A geologically plausible model of the crust in a virgin region has been presented along a Bouguer anomaly profile from Jaipur to Raipur.The following main conclusions have been drawn from the present analysis: (1) The depths to the Moho and Archaean basement interfaces fluctuate between 33.2 and 36.8 km and between 4.6 and 7.0 km respectively. (2) The Narmada‐Son Lineament (NSL) does not coincide exactly with the Moho upwarp beneath it. However, this offset is greater in the eastern part of the NSL rather than in the western part. (3) The development of the Satpura horst structure is due to a rise in the Moho interface in a compressional regime. (4) The intrabasement feature (depth from 5 to 12 km) represents a hybrid massif possibly formed due to an admixture of sialic and simatic crust under a tensional regime in the Ujjain‐Mahan section.