Study of 28th April, 2021 Mw 6.0 Assam earthquake in a part of eastern Himalayan foreland region, northeast India.

The northeastern part of India is seismically very active due to the ongoing Indian Plate under-thrusting and rise of several mountain ranges. As a result, the Himalayas, Naga Hills, Shillong-Karbi Massifs, and the Assam Valley have many crustal-scale active faults. These faults often cause moderate to large earthquakes while releasing the accumulated stress associated with Plate tectonics. In this study, one such major earthquake event of Mw 6.0 occurred near the Kopili Fault and Himalayan Frontal Thrust in the eastern Himalayan foreland region on 28th April 2021. The event has been investigated to understand its seismotectonic and environmental impacts. The quake caused much damage in the epicentral area around Dhekiyajuli of Sonitpur District, Assam, India. The densely populated Guwahati and Tezpur cities of Assam have suffered damage as some parts of buildings and roads were collapsed. Moreover, a landslide near Bhairabkunda and several liquefaction incidents near Tezpur and Dhekiyajuli localities were also recorded, within 30–50 km from the epicentre. It is found from NASA's GRACE-Land data that the increase in groundwater volume on the northern bank of the Brahmaputra than the previous year might be related to higher rainfall in the recharge zone around the Himalayan Frontal parts. Such groundwater conditions caused saturation of the subsurface soil and alluvium, which resulted in the formation of liquefaction during high shaking. These incidents also caused severe environmental damage. After the earthquake, the sprouting of mud water affected rice fields and nearby freshwater sources like ponds and lakes. This earthquake, along with the historical ones, reveals the vulnerability of the entire region to many natural hazards. This study provides a scope to understand the seismotectonic and environmental exposure of the eastern Himalayan foothill region. [ABSTRACT FROM AUTHOR]