Earthquakes are sudden movements of the Earth’s crust. They occur when the Earth’s plates move around on the viscous, or slowly flowing, mantle layer beneath them. This non-stop movement causes stress to build up in some areas of the Earth’s surface, which can lead to cracks called faults. When the pressure becomes too great, the rock on one side of the fault slips with respect to the other, which causes the earthquake.
When an earthquake occurs, the energy is transferred to the surrounding rocks through vibrations called seismic waves. These waves can be detected by instruments called seismometers. They can tell scientists where, when and how much the earthquake shook, or how much its magnitude was.
A very large earthquake is so intense that it can cause buildings to collapse or sink into the ground. This is because buildings were not designed or built to withstand this type of shaking. However, there have been very large earthquakes that caused little damage because they did not cause strong shaking and/or the buildings were built to withstand it.
The location of the center of an earthquake is known as the epicenter. An earthquake’s most intense shaking is felt near its epicenter, but the energy of the quake can be felt and even measured hundreds or thousands of miles away. The reason is that the Earth’s rocky crust is not rigid enough to transfer stress efficiently over long distances. Sometimes earthquakes in one place can trigger seismic activity over a wider area (thousands of miles). However, most of the time triggered earthquakes are small and short-lived.
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