Consider the following statements: 1. In a seismograph, P waves are

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?

1 only
2 only
Both 1 and 2
Neither 1 nor 2
This question was previously asked in
UPSC IAS – 2023
The correct answer is C) Both 1 and 2.
Statement 1 is correct. P waves (Primary waves) are compressional waves that travel fastest through the Earth’s layers. S waves (Secondary waves) are shear waves and travel slower than P waves. Therefore, P waves arrive at a seismograph before S waves from the same earthquake event.
Statement 2 is correct. P waves are longitudinal waves, meaning the particles of the medium vibrate back and forth in the direction of wave propagation. S waves are transverse waves, meaning the particles vibrate perpendicular (at right angles) to the direction of wave propagation.
P waves can travel through solids, liquids, and gases, while S waves can only travel through solids. This difference in behavior was crucial in understanding the Earth’s internal structure, particularly the liquid outer core which stops S waves.
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