The correct option is They exert pressure on the material in the direction of propagation, creating density differences..
Explanation
Earthquake waves are classified into Body Waves and Surface Waves. Body waves are generated due to the release of energy at the focus and move in all directions traveling through the body of the earth. They are further divided into P-waves (Primary waves) and S-waves (Secondary waves). P-waves are longitudinal waves that move faster than other seismic waves.
Option Analysis
- They vibrate perpendicular to the direction of wave propagation. is incorrect: P-waves vibrate parallel to the direction of the wave propagation. It is S-waves (Secondary waves) that vibrate perpendicular to the direction of wave propagation (transverse nature).
- They travel only through solid materials. is incorrect: P-waves can travel through gaseous, liquid, and solid materials. In contrast, S-waves can travel only through solid materials, which is a crucial property used to determine the state of the Earth's core.
- They exert pressure on the material in the direction of propagation, creating density differences. is correct: P-waves are compressional waves. As they propagate, they exert pressure on the material in the direction of propagation. This action creates compressions (squeezing) and rarefactions (stretching), resulting in density differences within the material.
- They are the last to arrive at the surface and cause the most destruction. is incorrect: P-waves are the first to arrive at the surface because they travel fastest. The waves that are the last to arrive are Surface waves, which are also responsible for the most structural destruction.
Key Takeaway: P-waves are longitudinal, compressional waves that travel through all states of matter (solid, liquid, gas) and are the fastest seismic waves to be recorded on a seismograph.