Earthquakes and Tsunamis

An earthquake is the sudden release of energy stored in rocks along a fault. As tectonic plates grind against one another, friction locks their edges while stress steadily accumulates. When the stress exceeds the strength of the rock, the fault ruptures and the stored elastic energy is released in seconds. The point underground where rupture begins is the focus, or hypocenter, and the point on the surface directly above it is the epicenter. The depth of the focus matters: shallow earthquakes, within about seventy kilometers of the surface, tend to cause the most damage because their energy has less distance to dissipate before reaching the ground people live on.

That energy radiates outward as seismic waves. Body waves travel through the Earth's interior. Primary (P) waves are fast, compre