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Delineation of major subsurface structural features and source depth locations using 3-D Euler deconvolution of gravity data at north-eastern part of India

Ghosh Gopal K.

Acta Geophysica

2022

Vol. 70, no 5

2033--2044

The convergence of different major tectonic plates, namely the Eurasian, Indian and Sunda plates, may be the cause of the Assam Syntaxis due to the tectonic interaction between the Himalayan and the Indo-Burman ranges. The study covers the area between latitude 23°–28° N and longitude 88°–96° E and has experienced various types of earthquakes in the recent past. Seismic activity occurs in and around the Shillong Plateau, Mikir Hills, Arakan-Yoma Fold Belt, Naga Hills, parts of the Bengal Basin, lower and upper Brahmaputra valley, and the Mishmi Hills of the Himalayan foothills. Still, part of the study area is extremely unreachable and a limited number of thrust-faults have been identified from field geological studies and GIS maps received from the various sources. In this paper, an attempt has been made to study the delineation of thrust-fault locations using available ground gravity data of northeastern India with the help of a three-dimensional Euler deconvolution technique using the least squares method. Gravity data suggest an undulating nature throughout the area; however, high gravity values are observed at the Bengal Basin and Shillong Plateau, whereas lower gravity values are observed at Brahmaputra and Assam valley, Indo-Burman Range and Molasse Basin. The Shillong Plateau has high gravity with high elevation, whereas the Bengal Basin has high gravity with low elevation. This means that certain tectonic resettlement takes place in the Shillong Plateau, which causes the higher gravity anomaly. The use of Euler deconvolution with the help of a structural index plays a major role in gaining a better understanding of thrust-fault delineation and provides a mappable solution in this area. In this study, source depth estimation using 3- dimensional Euler deconvolution has been carried out by applying a range of structural index and window sizes. The different combinations of structural index and window size during the Euler deconvolution process generates several solutions including some unwanted spurious noise. To remove this noise, unrealistic solutions are discarded by applying filtering criteria to obtain the desired acceptable depth. The results derived using 3-dimensional Euler deconvolution correlate well with the previous finding of thrust-fault delineation. The present study validates the thrust-fault boundaries as well as providing additional thrust-fault settings in the complex tectonic area. The gravity data interpretation appears to offer a reasonable approach for source depth estimation and structural boundary identification.