Final answer:
The fastest seismic waves are P-waves or pressure waves, which are longitudinal and travel at speeds of 4 to 7 km/s, faster in rigid materials and slower in less rigid ones. The correct option is A.
Step-by-step explanation:
The type of seismic waves that travel the fastest are the P-waves or pressure waves. P-waves are longitudinal waves and can travel at speeds of 4 to 7 km/s, depending on the rigidity of the material through which they are moving. They have a higher speed in more rigid materials like granite and are slower in less rigid materials such as sediments.
As the P-wave has a significantly higher speed compared to the S-wave, it arrives first at seismograph stations, providing an important lead time before the arrival of the more damaging S-waves and surface waves during an earthquake.
Hence, Option A is correct.