Which of the following statements regarding earthquakes is/are correct?

1. The point on the Earth's surface directly above the focus is called the epicentre of the earthquake.

2. Earthquakes generate Primary and Secondary waves that radiate outward from the earthquake focus.

3. Deep-focus earthquakes are likely to cause more damage than shallow-focus earthquakes.

Select the answer using the code given below:

The correct answer is 1 and 2 only.

Key PointsUnderstanding Earthquakes

• The point on the Earth's surface directly above the focus is called the epicentre of the earthquake:
  • The focus, also known as the hypocenter, is the point within the Earth where an earthquake rupture starts.
  • The epicenter is the point on the Earth's surface located directly above the focus.
  • This is a well-established geophysical term and is crucial for mapping and understanding the impact of an earthquake. Hence, statement 1 is correct.
• Earthquakes generate Primary and Secondary waves that radiate outward from the earthquake focus:
  • Primary waves (P-waves) are compressional waves that travel fastest through the Earth and can move through both solid and liquid layers.
  • Secondary waves (S-waves) are shear waves that travel slower than P-waves and can only move through solid materials.
  • These waves are crucial for understanding the internal structure of the Earth and for earthquake detection and analysis. Hence, statement 2 is correct.
• Deep-focus earthquakes are likely to cause more damage than shallow-focus earthquakes:
  • Deep-focus earthquakes occur at depths greater than 300 km, while shallow-focus earthquakes occur at depths less than 70 km.
  • Shallow-focus earthquakes generally cause more damage at the surface compared to deep-focus earthquakes because they are closer to the surface.
  • Deep-focus earthquakes lose much of their energy before reaching the surface. Hence, statement 3 is incorrect.

Additional Information

• Primary Waves (P-waves):
  • P-waves are the fastest seismic waves and are the first to be detected by seismographs.
  • They can travel through both solid rock and fluids, like water or the liquid layers of the Earth.
  • P-waves compress and expand the material they move through, similar to sound waves.
• Secondary Waves (S-waves):
  • S-waves are slower than P-waves and arrive at seismograph stations after the P-waves.
  • They can only move through solid rock, not through any liquid medium.
  • S-waves move the ground up and down or side-to-side, perpendicular to the direction the wave is traveling.
• Seismograph:
  • A seismograph is an instrument that measures and records details of earthquakes, such as force and duration.
  • It is crucial for monitoring seismic activity and for early warning systems.
• Earthquake Focus and Epicenter:
  • The focus (hypocenter) is the point inside the Earth where the earthquake originates.
  • The epicenter is the point directly above the focus on the surface of the Earth.
  • The distance between the focus and the epicenter can affect the intensity and distribution of seismic waves.
• Shallow-focus vs. Deep-focus Earthquakes:
  • Shallow-focus earthquakes are more common and tend to cause more damage due to their proximity to the Earth's surface.
  • Deep-focus earthquakes, while less common, can still be powerful but usually cause less damage on the surface.
  • The depth of an earthquake is a critical factor in determining its potential impact on buildings and infrastructure.