Why are P waves recorded before S waves?

Correct answer: P waves have higher speed

The direct answer is A: P waves are recorded before S waves because P waves travel faster. P waves are primary, compressional waves. They push and pull particles in the direction of travel and can pass through solids, liquids and gases. S waves are secondary, shear waves. They move particles at right angles to the direction of travel and can pass through solids but not liquids. If both waves start at the same earthquake and travel toward the same station through suitable material, the faster P wave covers the distance first. Option A is correct because higher speed produces earlier arrival. Option B is wrong because P waves are body waves and travel through Earth’s interior; they do not travel only along the surface. Option C is wrong because S waves are mechanical seismic waves, not light. Option D is wrong because S waves do not always arrive first; they generally arrive after P waves. A useful calculation idea is: for the same distance, a greater speed means a smaller travel time, using the relation travel time = distance ÷ speed. Remember the order P before S.