Previous Year Question
Given below are two statements, one is labelled as Assertion (A) and the other as Reason (R).
Assertion (A): The highest concentration of Seismic zones lies in Himalayan region in India.
Reason (R): There are many longitudinal thrust zones in Himalayas.
Codes:
Both (A) and (R) are true and (R) is the correct explanation of (A)
Both (A) and (R) are true, but (R) is not the correct explanation of (A)
(A) is true, but (R) is false
(A) is false, but (R) is true
Correct Answer: A
Detailed Solution
The Himalayas are among the most tectonically active regions of India. Convergence between the Indian Plate and the Eurasian Plate is still continuing, resulting in continuous generation and accumulation of crustal stress in the Himalayan region.
Several major longitudinal Thrust/Fault zones occur in the Himalayas. Particularly important among them are the Main Frontal Thrust (MFT), Main Boundary Thrust (MBT) and Main Central Thrust (MCT). These structures extend broadly parallel to the general trend of the Himalayan ranges.
Accumulation of stress and sudden movement along these thrusts and faults can generate earthquakes. The Geological Survey of India has also associated seismic activity in Himalayan regions with tectonic structures such as the MBT, MCT and local faults and lineaments.
In India's seismic zoning, large parts of the Himalayas fall within Zones IV and V, representing high to very high seismic hazard. According to BIS, Zone V is the most severe seismic zone.
Therefore, Reason (R) is not merely an independent fact; the numerous active thrust zones of the Himalayas are among the principal tectonic causes of the region's high seismicity.