Shallow-focus earthquakes tend to be larger, and therefore more damaging, earthquakes. This is because they are closer to the surface where the rocks are stronger and build up more strain. Other earthquakes, including deep-focus earthquakes, can originate in subduction zones, where one tectonic plate subducts, or moves under another plate. B Faults Stress in the earth's crust creates faults places where rocks have moved and can slip, resulting in earthquakes. The properties of an earthquake depend strongly on the type of fault slip , or movement along the fault, that causes the earthquake.
Geologists categorize faults according to the direction of the fault slip.
When the rock hanging over the dipping fault plane slips downward into the ground, the fault is called a normal fault . When the hanging wall slips upward in relation to the bottom wall, the fault is called a reverse fault or a thrust fault . Both normal and reverse faults produce vertical displacements, or the upward movement of one side of the fault above the other side, that appear at the surface as fault scarps. Strike-slip faults are another type of fault that produce horizontal displacements, or the side by side sliding movement of the fault, such as seen along the San Andreas fault in California. Strike-slip faults are usually found along boundaries between two plates that are sliding past each other.