There are two causes of earthquake. Movement of plates and Volcanism
An Earthquake (or quake or tremor) is the shaking of the surface of the Earth. Earthquakes can be extremely violent or so slight that they only register on instruments. They are caused by sudden movements of the Earth's tectonic plates.
The study of earthquakes is called seismology.[1] Earthquakes are usually quite brief, but may repeat. The sudden release of tension in the tectonic plates sends waves of energy that travel through the Earth. Seismology studies the cause, frequency, type and size of earthquakes.
There are large earthquakes and small earthquakes. Large earthquakes can take down buildings and cause death and injury. Earthquakes are measured using observations from seismometers. The magnitude of an earthquake, and the intensity of shaking, is usually reported on the Richter scale. The Richter Scale was invented by Charles Francis Richter in 1935. On the scale, 2 is scarcely noticeable, and magnitude 5 (or more) causes damage over a wide area.
An earthquake under the ocean can cause a tsunami. This can cause just as much death and destruction as the earthquake itself. Landslides can happen, too. Earthquakes are part of the Earth's rock cycle. The impact can be measured by a seismometer. It detects the vibrations caused by an earthquake. It puts these movement on a seismograph. The strength, or magnitude, of an earthquake is measured using the Richter scale. The Richter scale is numbered 0-9.Now the largest ever measured is 9.5.
Scientists cannot view a major earthquake beforehand. They do know where earthquakes may occur, such as close to the fault lines.
Advice on what to do in an earthquake:
a) If you are indoors:-
Take cover under a table or bench. If there is no table or desk, sit against a wall away from things that might fall on you and stay away from windows, bookcases or tall, heavy furniture.
Wait in your safety spot until the shaking stops and then check to see if you are hurt. Check others around you too. Move carefully and look out for fallen things.
There may be aftershocks or smaller earthquakes quite soon after. So be prepared.
If you want to leave the building after the shaking stops, use the stairs, never use elevators