EARTHQUAKES

Fault Line Earthquakes usually occur when the Earth’s crust moves along a fault, a break in the Earth’s crust, causing the location of the land to shift. There are basically three types of faults: normal, reverse and tear. Normal faults occur where the rocks pull apart and the rocks on the upper side of the fault slide downward. Reverse faults occur where the rocks are pushed together and the rocks on the upper side of the fault slide upwards. Tear faults move sideways instead of up and down, just as if the rocks were being torn apart.

This photo shows a fault line. If you follow the two gray layers with the white layer in between from left to right you will see the fault line.

The magnitude of an earthquake is sometimes measured on the Richter Scale (some scientists use other scales as well). The Richter Scale measures earthquakes on a scale of less than 1 (minor) to 10 (epic) and above. Earthquake with a magnitude less than 3 are not typically noticed by people but can happen up to 1,000 times each day. Earthquakes that have a magnitude of 7 or more typically cause the ground to shake noticeably and can cause damage to buildings and the land surface. There are usually less than 20 earthquakes each year that measure 7.0. Earthquakes greater than 7.0 are very rare and, in fact, a magnitude of 10 or higher has never been recorded. For more information on the Richter Scale and other scales used to measure earthquakes click here.

Earthquakes can occur both on land and under water. If the earthquake occurs under the ocean, a huge tidal wave, called a tsunami, can occur. Tsunamis are very dangerous and can flood a large area very quickly.