Seismic Waves: How Earthquakes Shake the Planet

Seismic waves are vibrations that spread through Earth after an earthquake or explosion.
They carry the released energy outward from the quake’s focus, shaking the ground.
P-waves (primary waves) are the fastest, compressing and expanding rock like sound waves.
S-waves (secondary waves) move more slowly, shaking the ground side to side or up and down.
P-waves can travel through solids, liquids, and gases, but S-waves only move through solids.
The difference in arrival times of P- and S-waves helps pinpoint an earthquake’s epicenter.
Surface waves travel along Earth’s crust, causing the most visible damage to buildings and roads.
Seismic waves reveal Earth’s hidden layers, since they bend and reflect inside the planet.
Seismologists record them with instruments called seismographs, which create quake “fingerprints.”
From minor tremors to massive quakes, seismic waves are Earth’s way of releasing built-up stress.