Which type of wave is the first to arrive at a distant location after an earthquake?

• A. P-waves
• B. S-waves
• C. Surface Waves
• D. Rayleigh Waves

Answer: (A)

When an earthquake happens, energy travels through the Earth as different kinds of waves that move at different speeds. The fastest are the P-waves, which are compressional and push and pull the ground in the direction the wave is moving. Because of their speed, these waves reach distant locations first. The next-fastest are the S-waves, which shear the ground back and forth perpendicular to the direction of travel and can only move through solids; they arrive after the P-waves. Surface waves travel along the Earth’s surface and typically move more slowly than the body waves, so they arrive even later. Rayleigh waves are a type of surface wave with a rolling motion, and they also arrive after the initial P- and S-waves. So the first signal at a distant site is from the compressional, fastest waves.