Earthquakes are an abrupt disturbance within the Earth's structure that generate seismic waves. Many earthquakes occur without being noticed by human beings but many are "felt quakes", as the passage of the seismic waves are felt above ground in the form of shaking, ruptures and movement of both the natural and built environments.
Earthquakes are often referred to as quakes, tremors or temblors.
Earthquakes can be minor through to very destructive. This is measured on a scale, to assist with understanding the kind of damage that may occur or have occurred from a particular size of earthquake. The moment magnitude scale is used for earthquakes over 5 reported globally. The Richter scale is used to report local magnitude earthquakes smaller than magnitude 5. The scales are similar in numbers, so that quakes of 3 or under are considered "weak", while quakes over 7 are considered strong and able to cause serious damage, dependent on their depth.
The Mercalli scale measures the intensity of the shaking.
Shallow earthquakes tend to cause greater damage to the built environment but this is dependent on other factors, such as the location, the ground surface, the geological makeup of an area, the strengths and weaknesses of the built environment, and so forth.