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Great Assam Earthquake, 1950

14 Aug 2025 GS 1 Geography
Great Assam Earthquake, 1950 Click to view full image

The quake occurred along the boundary where the Indian and Eurasian Plates collided, near the eastern terminus of the Himalayas, at a depth of 15 km. 

The rupture extended from the Mishmi thrust of the Eastern Himalayas to the Himalayan Frontal Thrust of Arunachal Pradesh, completing a curvilinear motion around the mountainous bend

Date & Magnitude

  • Occurred 15 August 1950, ~7:30 pm

  • Magnitude 8.6 – strongest recorded earthquake on land

  • Duration: 4–8 minutes shaking

  • Epicentre: ~40 km west of Rima (Zayu), Mishmi Hills, India–Tibet border

  • Depth: ~15 km

Impact

  • Felt over 3 million sq. km (India, Myanmar, Bangladesh, Tibet, South China)

  • Deaths: >1,500 in India; ~4,000 in Tibet

  • Cattle deaths: 50,000–1,00,000

  • Infrastructure destruction: railway tracks twisted, bridges collapsed, hills sheared, homes/farms destroyed

  • Secondary hazards: landslides blocked rivers → flash floods after dam bursts (Brahmaputra flood)

  • Widespread damage in Sibsagar–Sadiya (Assam) and Medog (Tibet)

Tectonic Setting

Due to plate rotation, major structural elements also take sharp turns, and the regional strike shifts from the general NE-SW direction to the NW-SE direction post-collision, forming what geologists call the Eastern Himalayan Syntaxis (EHS).

  • Occurred along Indian–Eurasian Plate boundary at the Eastern Himalayan Syntaxis (EHS)

  • Plate convergence rate: 10–38 mm/year (Eastern Himalayas)

  • Involves Indian Plate, Eurasian Plate, and Sunda Plate interaction → complex tectonics

  • Unlike typical thrust earthquakes in the Himalayas, the 1950 quake had a strike-slip component (lateral movement)
             a diagram of a strike-slip fault with a tree on top
             a diagram of a normal fault with a road and tree
             a diagram of a thrust fault is shown on a white background

  • Likely rupture from Syntaxial bend + activation of Himalayan thrust faults westward

  • Aftershocks: widely distributed east of main epicentre

Historical Seismicity

  • Records of major earthquakes in region: 1548, 1596, 1697 (Ahom period)

  • Geological evidence: major medieval quake between 1262–1635 AD

Significance

  • Provided early instrumental data 

  • India had the Meteorological Department (IMD) set up its first seismological observatory at Alipore in Kolkata district in 1898.

  • Enhanced understanding of Himalayan plate tectonics & seismic risk

Future Risk

  • Central & Eastern Himalayas remain highly seismically active

  • Magnitude ≥8.6 quakes possible along the 2,500 km Himalayan arc

  • Rising vulnerability due to urban growth, infrastructure (esp. dams) in fragile zones

Policy & Preparedness Lessons

  • Development in tectonically sensitive areas must consider seismic hazard mapping

  • Hydroelectric projects in Eastern Himalaya require rigorous seismic risk assessment

  • No prediction possible for exact timing/location – need for long-term resilience planning






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