Back2Basics: Earthquake and Related Terminologies

• Earthquake is a sudden shaking of the ground caused by energy release from tectonic plate movements or volcanic activity, generating seismic waves.
• Key Terminologies:

• • Focus (Hypocenter): The point inside the Earth where the earthquake originates, deep beneath the surface.
  • Epicenter: The point on the Earth’s surface directly above the focus, usually the most affected area.
  • Seismic Waves: Waves that carry the energy released during an earthquake and cause ground shaking.
  • Fault: A crack or fracture in the Earth’s crust where movement occurs, often causing earthquakes.
  • Magnitude: A measure of the earthquake’s size or energy, commonly measured on the Richter scale.
  • Intensity: The strength of shaking at specific locations, measured by the Modified Mercalli Intensity (MMI) scale.

Types of Earthquake Waves:

• Body Waves: Travel through the Earth’s interior, detected first by seismographs.
  • Primary Waves (P-Waves): Fastest, compression waves that move through solids and liquids.
  • Secondary Waves (S-Waves): Shear waves, slower than P-waves, that move through solids only.
• Surface Waves: Travel along the Earth’s surface, slower but cause more damage.
  • Love Waves: Move side-to-side horizontally, causing significant damage.
  • Rayleigh Waves: Cause elliptical ground motion, similar to ocean waves, very destructive.

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 waves 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?

(a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2