Lineament: Cause of Assam Earthquakes

An unfamiliar lineament is the major factor behind frequent earthquakes in the Sonitpur area of Assam. According to Geological Survey of India (GSI), the earthquakes in the region are frequent due to the following reasons:

  • East-West Trending Atherkhet Fault
  • Nrthwest-Southeast Trending Kopili Fault
  • North-south trending Lineament

The GSI has said that the Lineament is the main reason for the recent earthquake in Assam.

What is Lineament?

  • It is linear feature in a landscape (like a visible line or a long crack or a long visible dent). It is basically an expression of an underlying fault. Even ridges, troughs represent lineaments. A ridge is a long narrow elevated strip. Trough is a flat valley.
  • Lineaments are found in other planets and their moons as well.
  • Mineral resources are usually concentrated in areas of high-density lineaments. The Ranchi Mega Lineament is one such resource rich area.

Occurrence of Lineament

  • They might occur as a fault-aligned valley, a straight coast line, or as a series of fault or fold aligned hills or a combination of all these features.
  • The igneous intrusions, shear zones and fracture zones are also expressed as geomorphic lineaments.
  • The occurrence of lineament can be captured in a satellite photograph.

Local Scale Lineament and Global Scale Lineament

The Local Scale Lineament are associated with impacts that create large craters. On the other hand, Global Scale Lineament are associated with seismic waves. They are formed during large impacts that broke the stressed environment from their parent bodies.

What is Mega lineament?

The Mega Lineament is the term used to describe lineament on continental scale. San Andreas fault, Trans Brazilian Lineament are the mega lineament on the earth. They extend to thousands of kilometres.

Ranchi Mega Lineament

The data from IRS-1A and Landsat 5 were used to analyse the Chotanagapur plateau. It says that the Ranchi Mega Lineament is a potential site for base metal mineralisation. Also, it acts as good ground water conduit. However, Ranchi Mega Lineament is in Zone II in the Seismic Zone map of India. It means that it is in a low-risk zone.

Though it is a mega lineament, it is put in low-risk zone as compared to that of Assam, a very High-Risk Zone (Zone V). This is because, the fractures of Ranchi Mega Lineament are at great depths.

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