Earthquake produces which kind of sound before the main shock wave begins

The correct answer is infrasound.

Concept:

• When the Lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all round the earth. 
• These vibrations are called earthquakes.
• There are three types of earthquake waves:
  • P waves or longitudinal waves
  • S waves or transverse waves
  • L waves or surface waves
• An earthquake is measured with a machine called a seismograph. 
• The magnitude of the earthquake is measured on the Richter scale. An earthquake of 2.0 or less can be felt only a little. 
• An earthquake over 5.0 can cause damage from things falling. 
• A 6.0 or higher magnitude is considered very strong and 7.0 is classified as a major earthquake.

Explanation:​

• During the time of an earthquake, infrasound waves are produced before the mainshock.
• During this process there is a sudden release of seismic waves which causes the ground to shake and these seismic waves are classed as infrasound waves.
• Infrasonic waves are sound waves having a frequency less than the audible range, which is around 20 Hz.
• It can travel hundreds of kilometers through the surface of the earth.

Thus, earthquake produces infrasound before the main shock wave begins.

Additional InformationUltrasound

• Ultrasound or Ultrasonic waves are sounds with frequencies higher than the audible range.

Audible sound

• Audible sound are sounds with frequencies of 20 Hz to 20 kHz.