"Magnitude 5.3 Earthquakes Strike Tibet and Nepal's Mustang District"
P waves
compressional seismic waves; particles vibrate in the direction of propagation; arrive first at a seismograph.
S waves
transverse seismic waves; particles vibrate at right angles to propagation; arrive after P waves; cause more structural damage.
The Himalayas are geologically young fold mountains formed by the ongoing collision of the Indian Plate and the Eurasian Plate. This collision, which began roughly 50 million years ago and continues today, is the primary driver of seismic activity across the entire Himalayan arc, including Nepal and Tibet. The Indian Plate moves northward at approximately 5 cm per year. Where it cannot subduct cleanly beneath the Eurasian Plate, stress accumulates along fault lines and is periodically released as earthquakes. The Main Central Thrust (MCT) and the Main Boundary Thrust (MBT) are the two principal fault systems responsible for most major Himalayan earthquakes.
When an earthquake occurs, it releases energy in the form of seismic waves. Two types are critical for understanding earthquake detection and damage. P waves (primary or compressional waves) travel fastest and arrive first at a seismograph. In P waves, particles vibrate to and fro in the same direction as wave propagation. S waves (secondary or shear waves) travel more slowly and arrive later. In S waves, particles vibrate at right angles to the direction of propagation. S waves cause more structural damage because of this transverse motion. A seismograph records P waves before S waves, and the time gap between their arrival helps scientists calculate the distance to the epicentre.
The Himalayan region sits within Seismic Zone IV and V on India's seismic zonation map, the two highest-risk categories. Zone V covers the entire northeastern India, parts of Uttarakhand, Himachal Pradesh, Jammu and Kashmir, and the Andaman and Nicobar Islands. The causes of seismic hazard here differ from those in peninsular India. The Deccan Plateau is ancient, stable, and far from active plate boundaries, making its earthquakes infrequent and typically linked to reservoir-induced seismicity or intraplate stress. The Himalayas, by contrast, sit directly on an active convergence zone, making moderate-to-strong earthquakes a structural, recurring feature of the landscape rather than an anomaly.
The Mustang district of northwest Nepal, where the recent earthquake was centred near Lomanthang, lies in the upper Trans-Himalayan zone. This area is geologically distinct from the lower Himalayan ranges. It sits in the rain shadow north of the main Himalayan crest, with terrain more similar to the Tibetan Plateau than to the forested middle hills of Nepal. Despite its arid character, it is highly seismically active because it straddles the same convergent plate boundary that runs the length of the Himalayan arc.
The depth of an earthquake matters greatly for its surface impact. The Tibet earthquake was recorded at a depth of 35 km, placing it in the category of shallow-focus earthquakes (defined as those occurring above 70 km depth). Shallow-focus earthquakes cause more intense ground shaking at the surface than deeper earthquakes of the same magnitude, because the seismic energy travels a shorter distance before reaching populated areas. This is why even moderate-magnitude events in the Himalayas can trigger landslides, damage infrastructure, and cause casualties disproportionate to their Richter scale reading. …
Consider the following statements:
1.In a seismograph, P waves are recorded earlier than S waves.
2.In P waves, the individual particles vibrate to and fro in the direction of wave propagation whereas in S waves, the particles vibrate up and down at right angles to the direction of wave propagation.
Which of the statements given above is/are correct?
Discuss about the vulnerability of India to earthquake related hazards. Give examples including the salient features of major disasters caused by earthquakes in different parts of India during the last three decades.
Differentiate the causes of landslides in the Himalayan region and Western Ghats.
Consider the following statements:
1.In India, the Himalayas are spread over five States only.
2.Western Ghats are spread over five States only.
3.Pulicat Lake is spread over two States only.
Which of the statements given above is/are correct?
Consider the following statements regarding seismic waves:
1.P waves arrive at a seismograph before S waves.
2.In P waves, particles vibrate to and fro in the direction of wave propagation.
3.S waves cause more structural damage than P waves because of their transverse particle motion.
4.S waves can travel through both solid and liquid layers of the Earth.
How many of the above statements are correct?
Consider the following statements about the causes of landslides in the Himalayan region:
1.Tectonic earthquakes are a primary trigger because young fold mountain rock is already fractured and compressed.
2.Glacial Lake Outburst Floods (GLOFs) can trigger secondary landslides by undercutting valley slopes.
3.The causes of Himalayan landslides are fundamentally similar to those in the Western Ghats, with intense rainfall being the dominant trigger in both regions.
Which of the statements given above is/are correct?
With reference to earthquake focal depth, consider the following statements:
1.Shallow-focus earthquakes occur at depths less than 70 km.
2.Shallow-focus earthquakes generally cause more intense surface shaking than deep-focus earthquakes of the same magnitude.
3.Most Himalayan earthquakes are deep-focus events occurring below 300 km.
Which of the statements given above is/are correct?
Consider the following statements about India's seismic zonation:
1.India is divided into four seismic zones: Zone II, Zone III, Zone IV, and Zone V.
2.Zone V is the highest-risk zone and includes the entire northeastern region of India.
3.The Andaman and Nicobar Islands fall in Seismic Zone IV.
4.The Deccan Plateau is entirely in Seismic Zone II, the lowest-risk zone.
How many of the above statements are correct?
Match the following Himalayan fault systems with their primary role in regional seismicity:
List I (Fault System) — List II (Role)
A.Main Central Thrust (MCT) — 1. Separates the Lesser Himalayas from the Sub-Himalayas (Siwaliks)
B.Main Boundary Thrust (MBT) — 2. Separates the Greater Himalayas from the Lesser Himalayas
C.Main Frontal Thrust (MFT) — 3. The southernmost active fault; marks the Himalayan front against the Indo-Gangetic Plain
Select the correct answer:
Want the full note, Prelims Facts & MCQ answers?
Create a free account — takes less than a minute.
Create free account