Tectonic and Seismicity Characteristics of Bengal Basin System (BBS)

Daya Shanker, & Mir F. Karim

Published August 8, 2021, SCEC Contribution #11204, 2021 SCEC Annual Meeting Poster #185

The Bengal basin system is located in the Northeast corner of the Indian shield and consists of three sub-basins. Different basins show different tectonic patterns. Tectonic patterns of the region have been changing in different geological ages, which are well revealed by geological and geophysical evidence. Tectonics in Surma basin, West Bengal basin and deltaic region of Bangladesh are due to differential crustal movement owing to mantle plumes. Studies suggest that West Bengal basin shows North-South faulting trends, whereas, Surma basin shows East-West faulting pattern, however, central region of Bengal basin system shows faulting pattern mostly striking NW-SE. In the present study 38 year (1950-1988) seismicity and 16-year (1970-1985) P-wave first motion data have been used to determine the focal mechanism solutions and stress distribution. The faulting patterns are discussed in the light of northeast drifting of the Indian plate. The seismicity of the North and East of the basin are associated with Himalayan and Burmese thrust. The high thickness of sedimentary rocks may be due to upper mantle instability is the cause for accumulation of energy for earthquake generation and seismicity distribution in the region. Since the temperature at the source region is likely to be an important factor determining whether deformation occurs seismically or not. Evidences suggest that limiting temperatures for crustal and mantle materials are about 250o–450oC and 600o–800oC, respectively. As the upper crust and uppermost mantle have relatively higher strength (brittle) than the lower crust where aseismic, ductile deformation predominates, organizing a tectonic environment for earthquake occurrences in the region. However, triggering action is due to northeast drifting of the Indian Plate. The earthquake distribution trend, fault plane solutions, and their magnitudes advocates that a new arcual shaped tectonic belt striking Northwest-Southeast is developing across the Bengal basin system.

Key Words
P-wave first motion data, faulting pattern, mantle plume

Shanker, D., & Karim, M. F. (2021, 08). Tectonic and Seismicity Characteristics of Bengal Basin System (BBS). Poster Presentation at 2021 SCEC Annual Meeting.

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