Earthquakes occur almost everyday all over the world. Most of the time earthquakes are not strong enough to be felt by people, but the shaking caused by an earthquake can be recorded by a seismometer. These machines are located all over the world to ensure detection of earthquakes of all strengths. Only occasionally will a larger magnitude earthquake strike and cause damage to the region. There are many faults around the world and depending on where these faults are plays a major factor in determining where an earthquake will occur. It is these faults that are the reason for earthquakes. The information seismologists know about past earthquakes and earthquakes in general give them a limited ability to generally predict when and where earthquakes are going to occur.
An earthquake is the shaking of Earth’s surface caused by rapid movement of the earth’s rocky outer layer. “Earthquakes occur when tension stored in rocks suddenly releases” (Vogt 12). Faults occur at these places where rocks on either side of the crack have moved. Oceans are very common places for major tectonic plates to shift. When two plates separate, new oceanic crust is made near the fault as magma rises and eventually sets on the sea floor. If the plates on either side of the fault continue to spread then the ocean slowly becomes larger in width. This is called seafloor spreading. Mid-ocean ridges are characterized by a crack like valley at the fault. This crack like valley is caused by the tension pulling the plates apart, causing normal faulting to occur a number of times in the divergent boundary.
The most common type of fault is a normal or dip-slip fault. These occur when two blocks of earth are thrust toward each other, causing one to ride up over the other (Britt 1). “The hanging wall moves downward relative to the footwall” (Tarbuck 244). A reverse fault is the opposite of a normal fault. “The hanging wall moves upward relative to the footwall” (Tarbuck 244). A very powerful type of fault is the strike-slip fault that occurs when two plates slide past one another. The San Andreas Fault in California is a very good example of this type of fault. A great deal of damage is done when any type of fault shakes the soil under structures in a low-lying, waterlogged areas, causing liquefaction. Liquefaction occurs when an earthquake shakes the wet, sandy soil near a body of water.