Observing the impacts of 1950s great Assam earthquake in the tectono-geomorphological deformations at the Young Meghna Estuarine Floodplain of Bangladesh: evidence from Noakhali Coastal Region

Abstract

The 1950s great Assam earthquake (GAE) is considered the sixth largest earthquake of the twentieth century in South Asia caused by a collision of two continental plates. This earthquake affected the whole eastern half of the Indian subcontinent and significant tectono-geomorphological deformations were observed at the final course of the Ganges-Brahmaputra-Meghna (GBM) river processes. This is especially the case in the Young Meghna Estuarine Floodplain (YMEF) areas, which have rarely been investigated and documented. Thus, the present study examined the massive geomorphic changes and regarded the configuration changes of the YMEF area immediately after the event, along with its recent aspects. Several direct field surveys together with Focus Group Discussion (FGD), and Key Person Interview (KPI) were conducted within the study area from September 2018 to December 2019. The findings of these research initiatives were augmented by analyzing historical toposheets (1942 and 1964) and multi-temporal Landsat satellite imageries (1975–2019) of the region following appropriate research methodologies. Techniques of remote sensing (RS) and GIS integration were also implemented in a robust way to measure the sinuosity index (SI) of the Meghna River (MR) course that helped to identify the tectonic influences, geomorphic changes, and neotectonics of the study area. The study reveals that as a consequence of this devastating 1950s earthquake, the course of the mighty MR was severely distorted which resulted in a significant reduction of the water flow within its YMEF section. The findings of this study suggest massive configuration changes of the landmass and river course shifting due to this colossal earthquake event. The study also indicates the presence of considerable geomorphic instability along with extensive erosion, deposition, and bank line shifting of the river within the study area during the recent period.