Earthquakes
Science

A break in rock caused by tension forces, which causes rocks to slide downward
Normal fault
A break in rock caused by tension forces, which causes rocks to slide downward. Normal fault. A normal fault occurs when tension forces in the Earth's crust pull rocks apart, causing one block to slip downward.

A seismic wave that vibrates rock particles in the direction that it travels
Primary wave
A seismic wave that vibrates rock particles in the direction that it travels. Primary wave. A primary wave, or P-wave, is a type of seismic wave that compresses and expands material in the same direction it moves, quickly traveling through Earth's crust during an earthquake.

An area of few recent earthquakes, but with a history of strong quakes
Seismic gap
An area of few recent earthquakes, but with a history of strong quakes. Seismic gap. A seismic gap is a section of a fault that has not experienced significant earthquakes for a long time, suggesting it may be due for a future quake.

A break in rock where the two blocks move sideways, with little vertical movement
Strike slip fault
A break in rock where the two blocks move sideways, with little vertical movement, is called a strike slip fault. It is a type of fault where two blocks of the Earth's crust slide past each other horizontally.

A seismic wave that moves on a surface, it causes both up-and-down and side-to-side movement
Surface wave
A seismic wave that moves on a surface, it causes both up-and-down and side-to-side movement. Surface wave. In simple terms, a surface wave is a type of seismic wave that travels along the Earth's surface, causing shaking and movement.