Normal Fault

Normal Fault A normal fault acts in a way similar to a divergent boundary The difference between a normal fault and a divergent boundary is when a normal fault pulls apart, the hanging wall slides down. When a divergent boundary pulls apart, the two plates separate.

Under the Earth Convection in the earth moves the plates, and while this is happening stress is put onto the faults, which makes them eventually move.

Motions Underground & Formations on Top When the fault is put under enough stress, the hanging wall slides down, making an earthquake. Because most faults are under water, this creates a big wave when the fault shifts.

Focus Location and Magnitude The damage of an earth quake partially depends on the depth of the focus point, or hypocenter, within the earth. Earthquakes are divided into 3 categories depending on how deep the focus point is – shallow-focus (within 60 kilometers), intermediate focus (60-150 kilometers), and deep-focus (150+ kilometers) Since Earth’s lithosphere is typically only that deep on continents, deep-focus earth quakes occur on land or close to shore.

Focus & Rock Composition Even if a weak earthquake has a shallow hypocenter, it may cause a lot of damage because of the short distance that it has to travel to reach the surface. There isn’t a lot of crust above it to vibrate, so they are still strong. The deeper the hypocenter is, the more material on top needs to be vibrated by the energy from the earthquake, so it reduces the damage on earth’s surface. The mass of the surrounding material is important, too. For example, if the crust between the focus and the surface is mainly composed of a material like granite, the impact won’t be as bad compared to if it is a lighter material, like limestone.

Time and Magnitude The plates shift about two inches per year. The longer that the plate can’t move it’s two inches every year, the more stress is built up. Once the plate, or fault, finally shifts, there will be more movement. The longer that the plate is stuck will give the earthquake a greater magnitude.