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Q65 (IAS/2023) Geography › World Physical Geography › Seismology and volcanism Official Key

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?

Result
Your answer: —  ·  Correct: C
Explanation

The correct answer is Option 3 (Both 1 and 2) because both statements accurately describe the physical properties of seismic waves.

  • Statement 1 is correct: P-waves (Primary waves) are longitudinal waves that travel faster than S-waves (Secondary waves). Due to their higher velocity, P-waves are the first to be detected and recorded by a seismograph after an earthquake occurs, followed by the slower S-waves.
  • Statement 2 is correct: This describes the particle motion of each wave type. P-waves are compressional; particles vibrate parallel (to and fro) to the direction of energy propagation. In contrast, S-waves are transverse; particles move perpendicular (up and down or side to side) to the wave's path.

Since P-waves always precede S-waves and their respective vibration patterns are correctly identified, both statements are scientifically sound, making Option 3 the right choice.

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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. Consider the following statements : 1. In a seismograph, P waves are recorded earlier than S waves. 2. In P waves, the individual parti…
At a glance
Origin: From standard books Fairness: High fairness Books / CA: 10/10 · 0/10

This is a classic 'bread and butter' question directly from NCERT Class XI (Fundamentals of Physical Geography). It is a high-fairness static question. If you get this wrong, you are at a severe disadvantage because the 'serious crowd' will mark this with 100% accuracy. No current affairs linkage required.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
In a seismograph recording, are P waves recorded earlier than S waves?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Primary Waves (P-Waves) > p. 60
Presence: 5/5
“• Primary waves are called so because they are the fastest among the seismic waves and hence are recorded first on the seismograph.• P-waves are also called as the • longitudinal waves because the displacement of the medium is in the same direction as, or the opposite direction to, (parallel to) the direction of propagation of the wave; or• compressional waves because they produce compression and rarefaction when travelling through a medium; or• pressure waves because they produce a change in pressure in the medium.• P-waves create density differences in the material leading to stretching (rarefaction) and squeezing (compression) of the material.• P-waves are of relatively high frequency and are the least destructive among the earthquake waves.”
Why this source?
  • Explicitly states P-waves are the fastest seismic waves and therefore are recorded first on the seismograph.
  • Describes P-waves as longitudinal/compressional waves whose transmission properties explain their rapid arrival.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Secondary Waves (S-Waves) > p. 62
Presence: 5/5
“• Secondary waves (secondary they are recorded second on the seismograph) or S-waves are also called transverse waves or shear waves or distortional waves. They are analogous to water ripples or light waves. They arrive at the surface after the P-waves.• Transverse waves or shear waves mean that the direction of vibrations of the particles in the medium is perpendicular to the direction of propagation of the wave. Hence, they create troughs and crests in the material through which they pass (they distort the medium).• These waves are of high frequency and possess slightly higher destructive power compared to Pwaves.”
Why this source?
  • Labels S-waves as 'secondary' and notes they are recorded second on the seismograph.
  • Explicitly states S-waves arrive at the surface after the P-waves and are transverse (shear) in nature.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Why Do P-Waves Travel Faster Than S-Waves? > p. 61
Presence: 4/5
“• P-waves are about 1.7 times faster than the S-waves. P-waves are compression waves that apply a force in the direction of propagation and hence transmit their energy quite easily through the medium and thus travel quickly. On the other hand, S-waves are transverse waves or shear waves (the motion of the medium is perpendicular to the direction of propagation of the wave) and are hence less easily transmitted through the medium.”
Why this source?
  • Provides a quantitative speed relation: P-waves are about 1.7 times faster than S-waves.
  • Explains the physical reason (compression waves transmit energy more quickly than shear waves), supporting earlier arrival of P-waves.
Statement 2
In seismology, do particles in P waves vibrate to-and-fro in the direction of wave propagation (i.e., are P waves longitudinal)?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Primary Waves (P-Waves) > p. 60
Presence: 5/5
“• Primary waves are called so because they are the fastest among the seismic waves and hence are recorded first on the seismograph.• P-waves are also called as the • longitudinal waves because the displacement of the medium is in the same direction as, or the opposite direction to, (parallel to) the direction of propagation of the wave; or• compressional waves because they produce compression and rarefaction when travelling through a medium; or• pressure waves because they produce a change in pressure in the medium.• P-waves create density differences in the material leading to stretching (rarefaction) and squeezing (compression) of the material.• P-waves are of relatively high frequency and are the least destructive among the earthquake waves.”
Why this source?
  • Explicitly labels primary (P) waves as 'longitudinal' and equates this with particle displacement parallel to the wave direction.
  • Describes P-waves as compressional/pressure waves that produce compression and rarefaction along propagation.
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 2: The Origin and Evolution of the Earth > Propagation of Earthquake Waves > p. 20
Presence: 5/5
“Different types of earthquake waves travel in different manners. As they move or propagate, they cause vibration in the body of the rocks through which they pass. P-waves vibrate parallel to the direction of the wave. This exerts pressure on the material in the direction of the propagation. As a result, it creates density differences in the material leading to stretching and squeezing of the material. Other three waves vibrate perpendicular to the direction of propagation. The direction of vibrations of S-waves is perpendicular to the wave direction in the vertical plane. Hence, they create troughs and crests in the material through which they pass.”
Why this source?
  • Directly states P-waves vibrate parallel to the direction of the wave (to-and-fro along propagation).
  • Explains resulting stretching and squeezing (density differences) in the material along the propagation direction.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Why Do P-Waves Travel Faster Than S-Waves? > p. 61
Presence: 5/5
“• P-waves are about 1.7 times faster than the S-waves. P-waves are compression waves that apply a force in the direction of propagation and hence transmit their energy quite easily through the medium and thus travel quickly. On the other hand, S-waves are transverse waves or shear waves (the motion of the medium is perpendicular to the direction of propagation of the wave) and are hence less easily transmitted through the medium.”
Why this source?
  • Describes P-waves as compression waves applying force in the direction of propagation.
  • Links this compressional motion to efficient energy transmission and higher speed relative to S-waves.
Statement 3
In seismology, do particles in S waves vibrate at right angles to the direction of wave propagation (i.e., are S waves transverse)?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Secondary Waves (S-Waves) > p. 62
Presence: 5/5
“• Secondary waves (secondary they are recorded second on the seismograph) or S-waves are also called transverse waves or shear waves or distortional waves. They are analogous to water ripples or light waves. They arrive at the surface after the P-waves.• Transverse waves or shear waves mean that the direction of vibrations of the particles in the medium is perpendicular to the direction of propagation of the wave. Hence, they create troughs and crests in the material through which they pass (they distort the medium).• These waves are of high frequency and possess slightly higher destructive power compared to Pwaves.”
Why this source?
  • Explicitly names S-waves 'transverse'/'shear' and equates transverse with particle motion perpendicular to propagation.
  • States that transverse waves cause troughs and crests by perpendicular vibrations, matching the definition in the question.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Why Do P-Waves Travel Faster Than S-Waves? > p. 61
Presence: 5/5
“• P-waves are about 1.7 times faster than the S-waves. P-waves are compression waves that apply a force in the direction of propagation and hence transmit their energy quite easily through the medium and thus travel quickly. On the other hand, S-waves are transverse waves or shear waves (the motion of the medium is perpendicular to the direction of propagation of the wave) and are hence less easily transmitted through the medium.”
Why this source?
  • Describes S-waves as transverse/shear and specifies motion of the medium is perpendicular to propagation.
  • Contrasts with P-waves to reinforce the perpendicular nature of S-wave particle motion.
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 2: The Origin and Evolution of the Earth > Propagation of Earthquake Waves > p. 20
Presence: 5/5
“Different types of earthquake waves travel in different manners. As they move or propagate, they cause vibration in the body of the rocks through which they pass. P-waves vibrate parallel to the direction of the wave. This exerts pressure on the material in the direction of the propagation. As a result, it creates density differences in the material leading to stretching and squeezing of the material. Other three waves vibrate perpendicular to the direction of propagation. The direction of vibrations of S-waves is perpendicular to the wave direction in the vertical plane. Hence, they create troughs and crests in the material through which they pass.”
Why this source?
  • States S-wave vibrations are perpendicular to wave direction (in the vertical plane).
  • Groups S-waves with other waves that vibrate perpendicular, reinforcing the transverse classification.
Pattern takeaway: UPSC 2023 was tough, but it provided 'safety nets' in the form of pure static NCERT questions. The pattern shows that while Current Affairs can be random, Core Geomorphology remains loyal to standard texts. You cannot afford silly mistakes here.
How you should have studied
  1. [THE VERDICT]: Absolute Sitter. Source: NCERT Class XI Fundamentals of Physical Geography, Chapter 3 (Interior of the Earth).
  2. [THE CONCEPTUAL TRIGGER]: Geomorphology > Earth's Interior > Body Waves (P & S) vs Surface Waves (L & R).
  3. [THE HORIZONTAL EXPANSION]: Memorize the Shadow Zones: P-wave shadow is a band (105°-145°), S-wave shadow is a massive zone (>105°). Know the medium rules: P travels through Solid/Liquid/Gas (fastest in solid), S only through Solids. Know the destructiveness order: Surface Waves > S-waves > P-waves.
  4. [THE STRATEGIC METACOGNITION]: Do not skim the 'science' parts of Geography. The distinction between Longitudinal (Sound-like) and Transverse (Light-like/Ripples) waves is basic physics that UPSC loves to test in Geography. Visualizing the particle motion (push-pull vs up-down) is essential.
Concept hooks from this question
📌 Adjacent topic to master
S1
👉 P- and S-wave arrival order
💡 The insight

P-waves travel faster and are recorded before S-waves on seismographs.

High-yield for earthquake seismology questions: knowing arrival order is essential to reading seismograms and calculating epicentral distance. Connects to locating epicentres and interpreting seismic records in physical geography and geology questions.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Primary Waves (P-Waves) > p. 60
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Secondary Waves (S-Waves) > p. 62
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Why Do P-Waves Travel Faster Than S-Waves? > p. 61
🔗 Anchor: "In a seismograph recording, are P waves recorded earlier than S waves?"
📌 Adjacent topic to master
S1
👉 P-wave properties: compressional & fastest
💡 The insight

P-waves are compressional (longitudinal) waves that transmit energy rapidly through materials.

Important for explaining why P-waves reach stations first and for understanding seismic wave propagation through different layers; links to questions on wave types, wave speeds, and interior structure inference.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Primary Waves (P-Waves) > p. 60
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Why Do P-Waves Travel Faster Than S-Waves? > p. 61
🔗 Anchor: "In a seismograph recording, are P waves recorded earlier than S waves?"
📌 Adjacent topic to master
S1
👉 S-wave nature and shadow zone
💡 The insight

S-waves are shear (transverse) waves that arrive after P-waves and may be absent at certain distances (shadow zones).

Useful for questions on wave transmission, shadow zones, and what seismic records reveal about Earth's internal state (e.g., liquid outer core blocking S-waves). Helps answer mapping of seismic wave absence and travel-path reasoning.

📚 Reading List :
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 2: The Origin and Evolution of the Earth > Emergence of Shadow Zone > p. 20
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Secondary Waves (S-Waves) > p. 62
🔗 Anchor: "In a seismograph recording, are P waves recorded earlier than S waves?"
📌 Adjacent topic to master
S2
👉 P-waves: longitudinal (compressional) body waves
💡 The insight

P-waves involve particle motion parallel to propagation, producing compression and rarefaction along the travel direction.

High-yield for seismic wave classification questions; explains arrival order on seismographs and why P-waves penetrate all media. Connects to topics on wave types, material response (compressibility), and interior Earth studies; enables answering comparative and causal questions about wave speed and transmission.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Primary Waves (P-Waves) > p. 60
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 2: The Origin and Evolution of the Earth > Propagation of Earthquake Waves > p. 20
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Why Do P-Waves Travel Faster Than S-Waves? > p. 61
🔗 Anchor: "In seismology, do particles in P waves vibrate to-and-fro in the direction of wa..."
📌 Adjacent topic to master
S2
👉 S-waves: transverse (shear) waves
💡 The insight

S-waves involve particle motion perpendicular to propagation, producing shear deformation (troughs and crests).

Essential for contrasting with P-waves in exam questions; explains why S-waves cannot travel through fluids, contributes to understanding shadow zones and destructiveness. Links to material rigidity and seismic interpretation tasks.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Secondary Waves (S-Waves) > p. 62
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Why Do P-Waves Travel Faster Than S-Waves? > p. 61
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Secondary Waves (S-Waves) > p. 63
🔗 Anchor: "In seismology, do particles in P waves vibrate to-and-fro in the direction of wa..."
📌 Adjacent topic to master
S2
👉 Body waves vs Surface waves (paths and destructiveness)
💡 The insight

Body waves (P and S) travel through Earth's interior, while surface waves travel along the surface and cause greater damage.

Crucial for questions on seismic records, damage patterns, and probing Earth's interior; helps explain seismograph sectioning, arrival patterns, and why surface waves are most destructive. Enables reasoning on depth-related wave effects and hazard assessment.

📚 Reading List :
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 2: The Origin and Evolution of the Earth > Earthquake Waves > p. 19
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Secondary Waves (S-Waves) > p. 63
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 5: Earths Magnetic Field (Geomagnetic Field) > Shadow Zone For Both P Wave and S Wave > p. 64
🔗 Anchor: "In seismology, do particles in P waves vibrate to-and-fro in the direction of wa..."
📌 Adjacent topic to master
S3
👉 Transverse vs longitudinal seismic waves
💡 The insight

Distinguishes particle motion: transverse (perpendicular) for S-waves versus longitudinal (parallel) for P-waves.

High-yield for earthquake physics questions; helps answer questions about wave behavior, detection order, and effects on materials. Connects to topics on wave propagation, seismogram interpretation, and material response to stress.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Secondary Waves (S-Waves) > p. 62
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Why Do P-Waves Travel Faster Than S-Waves? > p. 61
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Primary Waves (P-Waves) > p. 60
🔗 Anchor: "In seismology, do particles in S waves vibrate at right angles to the direction ..."
🌑 The Hidden Trap

The 'Shadow Zone' angles are the next logical target. Remember: The S-wave shadow zone (beyond 105°) is much larger than the P-wave shadow zone (band between 105° and 145°). Also, P-waves 'refract' (bend) at the core-mantle boundary, while S-waves are completely stopped.

⚡ Elimination Cheat Code

Use the 'Name Mnemonic' Hack: 'P' stands for Primary (First arrival) and Pressure (Compressional/Longitudinal like sound). 'S' stands for Secondary (Second arrival) and Shear (Transverse/cutting movement). This linguistic link validates both statements without needing deep physics.

🔗 Mains Connection

Mains GS-3 (Disaster Management): Understanding P vs S waves is the basis of 'Earthquake Early Warning Systems' (EEWS). Sensors detect the faster, non-destructive P-waves to trigger alarms/shut gas lines seconds before the destructive S-waves and Surface waves arrive.

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SIMILAR QUESTIONS

CDS-II · 2024 · Q95 Relevance score: 2.62

Which one of the following statements regarding S-waves is not correct?

NDA-II · 2025 · Q115 Relevance score: 1.74

Which of the following statements with reference to shadow zones in an event of an earthquake is/are correct ? 1. Zone between 105° and 145° from epicentre was identified as the shadow zone for both P-waves and S-waves 2. The shadow zone of P-waves is much larger than that of the S-waves Select the answer using the code given below :

CDS-I · 2025 · Q1 Relevance score: 1.50

Consider the following statements with reference to Secondary waves (S-Waves) generated during an earthquake : 1. They create troughs and crests in the material through which they pass. 2. The direction of vibrations of S-waves is perpendicular to the wave direction in the vertical plane. Which of the statements given above is/are correct ?

CDS-I · 2006 · Q55 Relevance score: -0.03

Consider the following statements 1. Light waves can travel in vacuum. 2. Light waves can be refracted. 3. Light waves are electromagnetic. Which of the statements given above are correct ?

IAS · 2007 · Q76 Relevance score: -0.22

Consider the following statements: 1. A flute of smaller length produces waves of lower frequency. 2. Sound travels in rocks in the form of longitudinal elastic waves only. Which of the statements given above is/are correct?