P and S waves are associated with which phenomenon?

Concept — seismic body waves. A sudden release of stored elastic strain inside the Earth sends elastic waves through the planet. Waves that travel through the Earth's interior are called body waves.

P waves are compressional body waves whose particles move parallel to the direction of travel; S waves are shear body waves whose particles move perpendicular to it. P waves pass through solids and fluids, whereas S waves require a solid medium.

Application — identify the generating phenomenon. The required phenomenon must release elastic strain within the Earth and produce both kinds of body wave.

1. When rocks rupture or slip along a fault, their stored elastic energy is released from the focus.

2. That release produces P and S waves, which travel outward and are recorded by seismographs.

3. P waves arrive first because they travel faster; the later S-wave arrival helps seismologists locate and analyse the event.

Contrast with the other values.

• Floods involve the movement and accumulation of surface water, not a release of elastic strain inside the Earth.

• Wind energy comes from moving air in the atmosphere.

• Tidal energy comes from periodic ocean movement driven mainly by lunar and solar gravity.

Cross-check and result. A seismogram characteristically records the faster P-wave arrival before the S-wave arrival. Therefore, P and S waves are associated with earthquakes.