Lineament factor for Assam earthquake

An unfamiliar lineament is among four factors behind frequent earthquakes in northern Assam’s Sonitpur area.

• The past century saw several great earthquakes:
  • the 1905 Kangra earthquake
  • the 1934 Bihar-Nepal earthquake
  • the 1950 Assam earthquake
• In case of the Assam earthquake of 1950, we found that the reason for widespread devastation in the eastern Himalayan belt was due to dual ruptures on the Himalayan Frontal Thrust near Pasighat and on the Mishmi Thrust.
• However, preliminary data on this latest quake in Assam indicated that the quake occurred along the Kopili fault itself.
• According to the Geological Survey of India (GSI), Sonitpur district lies within a tectonically complex triangular area bounded by the east-west trending Atherkhet Fault, the northwest-southeast trending Kopili Fault and a north-south trending lineament.
• The two faults and the lineament, along with the oblique convergence of the Indian plate, have caused frequent earthquakes.
• The National Centre of Seismology recorded 29 earthquakes of magnitude varying from 2.6 to 4.7 in Sonitpur after the 6.4 tremblor on April 28 that damaged several buildings, bridges and a river embankment.

What is a lineament?

• A lineament is a linear feature in a landscape dictated by an underlying geological structure such as a fault.
• These have been variously named as 'fracture zones,' 'shear zones,' 'trend lines' and' tectonic trends'.
• Location: Typically a lineament will appear as a fault-aligned valley, a series of fault or fold-aligned hills, a straight coastline or indeed a combination of these features.

• Location: In India, lineaments or tectonic trends have been reported from some parts of the country which are based on stratigraphic, structural and geophysical data.
• Mapping: National Geomorphological and Lineamentmapping has been one of the major efforts to find out the major lineaments in India.
• It was done using remote sensing data, for mapping the diversity of landform in the country and was jointly executed by ISRO and GSI/Ministry of Mines, along with more than 15 partner institutions across the country.
  

• The preliminary analysis shows that the earthquake events are located near to Kopili Fault which is closer to Himalayan Frontal Thrust (HFT).
• The area is seismically very active falling in the highest Seismic Hazard zone V and are associated with collisional tectonics where Indian plate sub-ducts beneath the Eurasian Plate.
• HFT is also known as the Main Frontal Thrust (MFT).
  • It is a geological fault along the boundary of the Indian and Eurasian tectonic plates.
• Triangular area: According to the Geological Survey of India (GSI), Sonitpur district lies within a tectonically complex triangular area.

• • Faults: It is bounded by
    • The east-west trending Atherkhet Fault
    • The northwest-southeast trending Kopili Fault: The Kopili Fault is a 300-km northwest-southeast trending fault from the Bhutan Himalaya to the Burmese arc.
    • north-south trending lineament
  • Major reason: The two faults and the lineament, along with the oblique convergence of the Indian plate, have caused frequent earthquakes.
    • Both the Atherkhet and Kopili faults are said to be major reasons because of the tectonic complexity.
    • Atherkhet and Kopilli are active lineament which are involved in earthquake.
    • Atherkhet and Kopili are not the only faults that impact the Sonitpur region.

• Highly vulnerable: The northeast is demarcated as Seismic Zone V, which indicates a zone with high vulnerability.
• Movement of plate: The Indian plate is moving northeast toward the Eurasian plate in the Himalayan region, their oblique collision and release of stress and strain accumulated in the local tectonic or fault environments lead to earthquakes.
• The Siang Fracture
• Yemla Fault
• Namula Thrust
• Canyon Thrust
• Main Himalayan Thrust
• Main Boundary Thrust

Main Central Thrust

Assam earthquake has brought the focus back on smaller faultlines like Kopili, as scientists stress on the need for more studies and data on the region’s lesser known seismicity. Furthermore, there is a lot of scope to improve data collection and dissemination for seismic events in order to handle the situation in a better way.