Question

When an earthquake occurs, the fastest wave is called a primary wave, or compression wave (P wave). This wave produces:

A) a back-and-forth motion on the surface of the earth
B) an up-and-down motion on the surface of the earth

Answer 1

Answer: (A) a back-and-forth motion on the surface of the earth

Explanation:

Earthquake generates seismic waves which are longitudinal waves.Longitudinal waves travel parallel in the direction of transfer of energy. Meaning that they travel in back and forth motion.

Longitudinal waves consist of compressions and rarefactions. When compressions occur when particles are close together and are regions of high pressure. Whereas, rarefactions occur when particles are further apart and regions of low pressure.

Answer 2

Answer: Option (A)

Explanation: P waves are the primary seismic waves that travels at a speed of about 4-8 km/sec. It is the fastest wave. During an earthquake, this P wave along with S wave is generated, where S wave is known as the secondary waves.

P waves produces a back and forth type of motion, due to their compression and dilation effect when propagates through a rock medium in their direction of propagation. The rocks under the earth's surface undergoes compaction and extension due to this effect. It releases a certain amount of energy because of this wave propagation under the earth's surface.

Thus, the correct answer is option (A).