The Great Assam Earthquake of 1950

On August 15, 1950, while India was celebrating its Independence Day, a devastating earthquake struck at 7:30 pm, with a magnitude of 8.6, marking it as the strongest recorded earthquake on land. The earthquake had a profound impact, primarily in Northeast India, along with effects felt across Myanmar, Bangladesh, Tibet, and South China.

Geographical and Seismological Overview

• The earthquake occurred at a depth of 15 km along the boundary where the Indian and Eurasian Plates collided, near the eastern terminus of the Himalayas.
• The rupture extended from the Mishmi thrust of the Eastern Himalayas to the Himalayan Frontal Thrust of Arunachal Pradesh.

Impact and Destruction

• Significant destruction of infrastructure: homes, farms, railway tracks, and bridges experienced severe damage.
• On the Indian side, more than 1,500 people died, and between 50,000 and 100,000 cattle were killed.
• Much destruction was reported from the Sibsagar-Sadiya area in Assam.
• Severe damage and a high number of casualties occurred in regions of Tibet, including the collapse of Yedong village into the Yarlung Zangbo River.
• After the earthquake, landslides blocked rivers, leading to flash floods that caused further destruction and loss of life.

Geological Insights

• The Great Assam Earthquake was instrumental in advancing the understanding of plate tectonics and seismic activities in the region.
• The earthquake displayed a component of strike-slip motion, differing from the typical thrust mechanism of Himalayan earthquakes.
• GPS data suggest complex tectonic activity in the Eastern Himalayas, with the convergence of Indian and Eurasian plates ranging from 10 mm to 38 mm/year.
• The Eastern Himalayan Syntaxis (EHS) is a key region where the earthquake likely originated, characterised by structural complexity and plate rotation.

Historical Context and Future Implications

• Historical records and geological studies indicate that the Northeast India region has experienced several significant earthquakes in the past.
• The earthquake underscored the potential for major seismic events in the Himalayas, suggesting the Central Himalayas are particularly vulnerable.
• Today, increased urbanisation and infrastructural developments have heightened vulnerability to earthquakes.
• Future developmental activities, including hydroelectric projects in the Eastern Himalayas, must consider the seismic risks.

Overall, the Great Assam Earthquake serves as a stark reminder of the seismic hazards in the Himalayan region. As the Indian plate continues its tectonic journey, preparedness and cautious development are essential to mitigate future risks.