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The Himalayas gives rise to numerous river systems in India, which emerges from the mountainous catchment and enters into the adjoining plain. With the sudden drop in the energy, the river deposits its load, forming the conical landforms, known as Alluvial Fan. These depositional loading and landforms are dynamic in nature and are controlled by the climatic factors and tectonics of the region. Based on the size and characteristics, the larger extend of the fan deposits are also known as megafans. In this study, five megafans extending from west to east, as Yamuna-Ganga, Sharda, Gandhak, Kosi and Tista megafans are studied, with the aerial extent from Delhi to Jalpaigudi.
Although individual megafans are well studied in terms of depositional patterns and morphology but a comprehensive study to investigate the fans using unified set of parameters to understand possible tectonic control on fan development is not well understood. Further, the role of basement depth and structures on the formation of the alluvial fan system is under studied. Thus, present study was attempted to relate the basement structural controls over the fan system using satellite gravity and multispectral data.
The optical data (e.g. LANDSAT 8, Sentinel 2) derived image products like Band Ratios and Principal Components (PCs), along with the topographic data were used to delineate the fan boundaries. The Bouguer Gravity Anomaly (BGA) derived from EIGEN-6C4 model was used to understand the subsurface response. The Basement depth (BD) and tilt derivate from the BGA were calculated for the entire megafan region using the edge detection techniques, to delineate the shallow basement structures.
The high sediment depth was observed towards the eastern margin i.e. towards Kosi and Tista megafan. The combined optical derived surface structures and shallow basement structure shows cumulatively complex tectonic features, thus indicating the predominate tectonic controls along the Kosi –Tista Megafan boundary, which further require extensive field based correlation and ground based geophysical survey to substantiate the finding.