Video narration
What happens underground before the ground begins to shake? Imagine a jammed drawer: you push, it holds, then suddenly gives way. Deep below, rock layers are squeezed from opposite sides. Along a fault-a break in the rock-the layers stay stuck while pressure builds. Many earthquakes begin when an existing fault slips; no new crack is needed. The ground does not start shaking first. Stressed rock suddenly slips, releasing energy. The focus is the underground point where the rupture begins. Energy spreads from there as seismic waves-shaking that travels through rock in every direction. The point directly above the focus at the surface is the epicenter. Waves travel upward and reach the surface, where the ground moves. Buildings may sway and roads can crack, but damage is not inevitable. So what starts the shaking? Rock slips underground, sending waves outward to shake the ground above.