Lineament Among Earthquake Factors

In News

Recently, it has been found out that an unfamiliar lineament is among the major factors behind frequent earthquakes in northern Assam’s Sonitpur area.

Major Findings

• The National Centre of Seismology (NCS) recorded 29 earthquakes of magnitude varying from 2.6 to 4.7 in Sonitpur.
• Water also started oozing out of the fault in Sonitpur and adjoining affected areas as a result of severe liquefaction from the unconsolidated substratum.
  • Liquefaction causes otherwise solid soil to behave temporarily as a viscous liquid. The phenomenon occurs in water-saturated unconsolidated soils affected by seismic waves, which cause ground vibrations during earthquakes.
  • Substratum is the underlying layer of soil/rock. It lies under the surface of another layer, or a feature that is less obvious than other features.
• According to the Geological Survey of India (GSI), Sonitpur district lies within a tectonically complex triangular area.
• It is 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.
• Both the Atherkhet and Kopilli are active but scientists do not know about the nature of the lineament involved.
• The northeast is demarcated as Seismic Zone V, which indicates a zone with high vulnerability.
  • 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 and Canyon Thrust are spread across the northeast and are active along with Main Himalayan Thrust, Main Boundary Thrust, Main Central Thrust and several subsidiary faults.

About Lineament

• It is a linear feature in a landscape that is an expression of an underlying geological structure such as a fault, fracture, or joint.
• These are usually associated with faults and linear zones of fracturing, bending deformation, and increased permeability of the crust.
• Typically, it appears as a fault-aligned valley, a series of fault or fold-aligned hills, a straight coastline or indeed a combination of these features.
• Lineaments are generally referred to in the analysis of remote sensing of fractures or structures. 
• Those fractures delineate prominent rectangular or rhomboidal blocks, some of which have been raised to form uplands and others have been depressed to form lowlands or topographic basins.
• Lineament map of India 

(Image Courtesy: RG)

Source: TH