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?

Key PointsP and S Waves:

• Body waves are generated due to the release of energy at the focus and move in all directions travelling through the body of the earth.
• There are two types of body waves.
  • They are called P and S-waves.
• P-waves:
  • They move faster and are the first to arrive at the surface.
  • These are also called ‘primary waves’.
  • The P-waves are similar to sound waves.
  • They travel through gaseous, liquid and solid materials.
  • P waves are characterized by a back-and-forth motion of particles parallel to the direction of wave propagation.
  • On the other hand, S waves, also known as secondary waves or shear waves, cause particles to vibrate perpendicular to the direction of wave propagation, creating an up-and-down or side-to-side motion. Hence statement 2 is correct
• S-waves:
  • They arrive at the surface with some time lag.
  • These are called secondary waves.
  • An important fact about S-waves is that they can travel only through solid materials.

Seismograph:

• In a seismograph, P waves are recorded earlier than S waves.
• P waves, also known as primary waves or compressional waves, are the fastest seismic waves and can travel through both solids and liquids.
• They arrive at a seismograph station before the arrival of S waves, which are slower and arrive after the P waves.
• Therefore, P waves are recorded earlier than S waves in a seismograph. Hence statement 1 is correct