Which seismic waves travel the fastest and are recorded first at a seismic station?

Which seismic waves travel the fastest and are recorded first at a seismic station?

• A. P waves
• B. S waves
• C. L waves
• D. Surface waves

Answer: (A)

The fastest seismic waves are P waves, the compressional or longitudinal waves. They move rock particles back and forth in the same direction as the wave travels, like sound waves. Because this motion is very efficient for pushing and pulling through materials, P waves travel faster than the other wave types and can pass through solids, liquids, and gases. That speed lets them arrive at a seismic station first after an earthquake. S waves, the shear waves, shake the ground perpendicular to the direction of travel and can only move through solids, not liquids. They travel slower than P waves, so they arrive after the P waves. Surface waves—Love and Rayleigh waves—travel along the Earth's surface and usually have even lower speeds than the body waves, plus their motion is more complex. They typically arrive last and often cause the most intense ground shaking near the epicenter. So the notice of the arrival order—P waves first, followed by S waves, then surface waves—is why P waves are recorded first.

The fastest seismic waves are P waves, the compressional or longitudinal waves. They move rock particles back and forth in the same direction as the wave travels, like sound waves. Because this motion is very efficient for pushing and pulling through materials, P waves travel faster than the other wave types and can pass through solids, liquids, and gases. That speed lets them arrive at a seismic station first after an earthquake.

S waves, the shear waves, shake the ground perpendicular to the direction of travel and can only move through solids, not liquids. They travel slower than P waves, so they arrive after the P waves.

Surface waves—Love and Rayleigh waves—travel along the Earth's surface and usually have even lower speeds than the body waves, plus their motion is more complex. They typically arrive last and often cause the most intense ground shaking near the epicenter.

So the notice of the arrival order—P waves first, followed by S waves, then surface waves—is why P waves are recorded first.