Which of the following statements is/are correct?

1. Secondary waves are compressional waves that are longitudinal in nature.

2. Primary waves are shear waves that are transverse in nature.

The correct answer is Neither 1 nor 2.

Key Points

Primary Waves:

• Primary waves (P-waves) are compressional waves that are longitudinal in nature. Hence, Statement 1 is incorrect.
• P waves are pressure waves that travel faster than other waves through the earth to arrive at a seismograph.
• These waves can travel through any type of material, including fluids as well as solid.
• They travel faster than S-waves.

Secondary Waves:

• Secondary waves (S-waves) are shear waves that are transverse in nature. Hence, Statement 2 is incorrect.
• S-waves can travel only through solids, as fluids (liquids and gases) do not support shear stresses.
• S-waves are slower than P-waves.

Important Points

• Earthquake waves get recorded in seismographs located at far off locations.
• It has been inferred indirectly using the time of travel of refracted and reflected seismic waves created by earthquakes.
• The changes in seismic velocity between different layers cause refraction due to Snell's law.
• S wave shadow zone forms the boundary of the outer core as it is in a liquid state.
• There exist some specific areas where the waves are not reported. Such a zone is called the ‘shadow zone’.