Articles written in Journal of Earth System Science

    • Modelling discontinuous well log signal to identify lithological boundaries via wavelet analysis: An example from KTB borehole data

      Amrita Singh Saumen Maiti R K Tiwar

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      Identification of sharp and discontinuous lithological boundaries from well log signal stemming fromheterogeneous subsurface structures assumes a special significance in geo-exploration studies. Well logdata acquired from various geological settings generally display nonstationary/nonlinear characteristicswith varying wavelengths and frequencies. Modelling of such complex well-log signals using the conventionalsignal processing techniques either fails to catch-up abrupt boundaries or at the best, do notprovide precise information on insidious lithological discontinuities. In this paper, we have proposed anew wavelet transform-based algorithm to model the abrupt discontinuous changes from well log databy taking care of nonstationary characteristics of the signal. Prior to applying the algorithm on thegeophysical well data, we analyzed the distribution of wavelet coefficients using synthetic signal generatedby the first order nonstationary auto-regressive model and then applied the method on actual welllog dataset obtained from the KTB bore hole, Germany. Besides identifying the formation of layeredboundaries, the underlying method also maps some additional formation boundaries, which were hithertoundetected at the KTB site. The results match well with known geological lithostratigraphy andwill be useful for constraining the future model of KTB bore hole data.

    • Mapping of basement structure beneath the Kohima Synclinorium, north-east India via Bouguer gravity data modelling


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      Kohima Synclinorium is one of the most tectonically active corridors of Indian subcontinent and displays complex tectonics of the region. Mapping the basement structure beneath the Kohima Synform is, therefore, vital to provide deep insight into the understanding of the crucial thrust geometry of the region. The vertical gravity gradient anomalies and available geological evidences suggest that the underlying area is occupied by thrust geometry embedded with prominently known tectonic trends of Schuppen Belt (SB), Kohima–Patkai Synclinal (KS–PS) and adjoining Inner Fold Belts (IFB). By keeping in view the massive complex tectonic upheaval in the region, we carried out 2D Bouguer gravity data analysis using the radially averaged power spectral techniques and GMSYS modelling to map the basement depth more precisely. Our results suggest that there is a wide range of heterogeneity in the underlying undulating basement indicating an average sedimentary thickness of the order of 2.2–5.5 km. The gravity PDEPTH modelling results show that source depth varies from 2.5 to 6.5 km. There is an uplifted basement tending towards the southwestern part while gradual deepening of basement was observed towards the eastern part of the study area. The profile modelling results show the presence of basement in a depth range of 2.5–3.8, 3.8–4.0, and 3.8–4.2 km beneath Foreland Basin (FB), Kohima–Patkai Synclinal structures (KS–PS), and Inner Fold Belts (IFB), respectively. The underlying results of integrated profiles, PDEPTH and GMSYS modelling would be useful to understand the detailed basement structure and tectonic trends of Belt of Schuppen (BS), Kohima–Patkai Synclinal structures (KS–PS) and adjacent Inner Fold Belts (IFB) of north-eastern region of India.

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