The Earthquake Archives

11. Which one of the following statements regarding S-waves is not corre

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

S-waves are slower than P-waves.

During an earthquake S-waves are less destructive to structures like buildings and highway overpasses.

S-waves can travel only through solids and cannot travel through the Earth's outer core.

Seismologists have concluded that the Earth's outer core must be liquid or fluid.

This question was previously asked in

UPSC CDS-2 – 2024

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Statement A is correct. P-waves (primary waves) are compressional waves and travel faster through the Earth’s layers than S-waves (secondary waves), which are shear waves. P-waves are the first to arrive at a seismic station.

Statement B is incorrect. S-waves cause particles to move perpendicular to the direction of wave propagation, resulting in a shearing motion. This sideways and vertical shaking motion is generally more damaging and destructive to structures like buildings, bridges, and overpasses compared to the push-pull motion of P-waves.

Statement C is correct. S-waves can only travel through solid materials because they rely on the rigidity of the medium to transmit the shear force. Liquids and gases have no rigidity, so S-waves cannot propagate through them. The Earth’s outer core is known to be liquid.

Statement D is correct. The observation that S-waves generated by earthquakes do not pass through the Earth’s outer core is the primary seismological evidence indicating that the outer core is in a liquid or fluid state.

– S-waves are slower than P-waves.
– S-waves are generally more destructive than P-waves due to their shearing motion.
– S-waves cannot travel through liquids.
– The absence of S-waves in the outer core indicates it is liquid.

Seismology, the study of earthquakes and seismic waves, is the main tool used by geophysicists to understand the internal structure and composition of the Earth. P-waves can travel through solids, liquids, and gases, albeit at different speeds.

12. Which one of the following is the other term used for ‘Focus’ in relat

Which one of the following is the other term used for ‘Focus’ in relation with an earthquake?

Hypocentre

Epicentre

Isocentre

Principal Point

This question was previously asked in

UPSC CDS-2 – 2022

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In seismology, the ‘focus’ is the point within the Earth where an earthquake originates, i.e., where the rupture begins. Another term for the focus is ‘hypocentre’.

The ‘epicentre’ is the point on the Earth’s surface directly above the focus. The intensity of an earthquake is often highest at the epicentre.

Seismic waves radiate outwards from the focus (hypocentre). The depth of the focus below the epicentre is known as the focal depth.

13. The extent of damage caused by earthquake is not influenced by which

The extent of damage caused by earthquake is not influenced by which one of the following ?

Strength of earthquake

Population density

Type of building

Climate of the area

This question was previously asked in

UPSC CDS-2 – 2021

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The correct option is D) Climate of the area.

The extent of damage caused by an earthquake is primarily influenced by factors related to the earthquake’s characteristics and the vulnerability of structures and populations in the affected area.

The strength of the earthquake (magnitude and intensity) directly determines the ground shaking level. Population density affects the number of people and infrastructure exposed to the shaking. The type and quality of building construction significantly influence their resistance to seismic forces; poorly constructed buildings suffer more damage. The climate of the area (temperature, rainfall, etc.) has no direct influence on the physical damage caused by seismic waves.

14. With reference to earthquakes, which of the following statements are c

With reference to earthquakes, which of the following statements are correct?

1. Earthquakes largely occur along the converging plate boundaries.
2. Point of origin of earthquake in lithosphere is known as focus/hypocentre.
3. Intensity of earthquake decreases with distance from the epicentre.
4. Epicentre of earthquake always remains over continents only.

Select the correct answer using the code given below.

1 and 2 only

1, 2 and 3

2 and 3 only

1 and 4

This question was previously asked in

UPSC CDS-2 – 2016

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Statements 1, 2, and 3 correctly describe aspects of earthquakes. Statement 4 is incorrect.

1. Earthquakes are indeed largely concentrated along plate boundaries, especially convergent (subduction and collision zones) and transform boundaries, where tectonic stresses are highest.
2. The focus (or hypocentre) is the exact point within the Earth’s lithosphere where the seismic rupture originates.
3. The intensity of ground shaking and damage caused by an earthquake typically decreases as distance from the epicentre (the point on the surface directly above the focus) increases, as seismic waves lose energy as they travel.
4. Earthquakes occur in both continental and oceanic lithosphere. The epicentre can be located anywhere on the Earth’s surface, including over oceans (e.g., associated with mid-ocean ridges, oceanic trenches, or transform faults in oceanic crust).

The magnitude of an earthquake (e.g., on the Richter or Moment Magnitude scale) measures the energy released at the source, while intensity (e.g., on the Modified Mercalli scale) measures the effect of the earthquake on people, buildings, and the environment at a particular location.

15. Which one of the following statements about primary waves of earthquak

Which one of the following statements about primary waves of earthquakes is not correct ?

They are similar to sound waves.

They can travel only through solid materials.

They travel through gaseous, liquid and solid materials.

They move faster and are the first to arrive at the surface.

This question was previously asked in

UPSC CDS-1 – 2021

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Primary waves (P-waves) are compressional waves and are the fastest type of seismic wave. They can travel through all states of matter: solid, liquid, and gas. Statement B claims they can travel *only* through solid materials, which is incorrect as they also pass through liquids and gases.

– Earthquake waves are mainly of two types: Body waves (P and S waves) and Surface waves (Love and Rayleigh waves).
– P-waves are primary waves, S-waves are secondary waves.

P-waves are similar to sound waves (longitudinal waves). S-waves (shear waves) can only travel through solid materials because they involve particle motion perpendicular to the direction of wave propagation, which is not supported in fluids (liquids and gases). P-waves arrive first at a seismic station because they are faster than S-waves and surface waves.

16. Tsunami waves are the undersea occurrence of earthquake exceeding 7.5

Tsunami waves are the undersea occurrence of earthquake exceeding 7.5 on Richter scale. Which one of the following statements regarding this is not correct?

It often generates strong waves.

The Pacific coasts are most vulnerable to Tsunami waves.

Tsunami waves are also called high-energy tidal waves or seismic sea waves.

Tsunami is a Latin word.

This question was previously asked in

UPSC CDS-1 – 2017

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Statement D is incorrect. The word “Tsunami” (津波) is Japanese, meaning “harbour wave”.

Tsunamis are giant waves caused by large-scale disturbances, most commonly underwater earthquakes, but also volcanic eruptions, landslides, and asteroid impacts. They are often referred to as seismic sea waves. The Pacific coasts, especially those bordering the seismically active “Ring of Fire”, are the most vulnerable to tsunamis. Tsunamis generate powerful waves that can cause immense destruction upon reaching coastlines.

Unlike wind-driven waves that only affect the surface, tsunamis are ‘full-column’ waves, meaning they displace the entire water column from the sea floor to the surface. In the open ocean, tsunamis have low amplitude but travel at high speeds. As they approach shallow coastal waters, their speed decreases, and their amplitude dramatically increases, leading to destructive wave heights. The term “tidal wave” is a misnomer, as tsunamis are not caused by tides.