Fault Reptures

Earthquakes are caused by a sudden movement of rocks along a fault plane. The movement or displacement is called the "Fault Rupture".

The rupture begins at some depth called the focus or hypocenter. The rupture then spreads outward in all directions along the fault plane.

When the fault rupture progresses upward and reaches the Earth's surface, it creates surface fault ruptures.

This is what this section is all about.

Surface fault ruptures come in all shapes and sizes but do not occur with every earthquake. They only happen when the quake is of sufficient size and is shallow enough whereby the fault rupture can break the surface.

The lowest magnitude earthquake to create surface fault ruptures is about a mid to upper M5 event. The focal depth must be shallow and on the order of less than 10 km and more like 2-6 km.

Many large, shallow earthquakes occur in the oceans but for us to see them, they must also occur on land.

Generally speaking, the larger the earthquake, the larger the potential surface fault rupture. Shallow earthquakes registering about M6.0 produce surface fault ruptures on the order of 2 feet and quakes of M8.0 generate ruptures on the order of 30-50 feet. It is extremely rare when the maximum surface fault ruptures exceed 50 ft.

Each earthquake has its own specific characteristics which govern its rupture behavior. Whether horizontal or vertical, or a combination of both, surface fault ruptures are spectacular.