Earthquake is the sudden shaking of the Earth’s surface caused by movements just below our planet’s outer layer – the crust. We know that earthquakes can be caused by faults, volcanic eruptions, landslides and even nuclear weapons tests! But they most often happen naturally, resulting from pressures building up within the Earth.
These pressures are created when tectonic plates grind together or slide past each other like puzzle pieces on top of a table – the movement is called plate tectonics. Sometimes the edges of these plates get stuck, creating friction. This friction causes stress, which may eventually make one of the tectonic plates suddenly slip, creating an earthquake!
An earthquake’s magnitude is a measure of how much energy was released. It is a number calculated from data collected by instruments called seismographs. The point where the earthquake starts, or its focus, is located beneath the ground, while the point directly above on the surface is called the epicenter.
In addition to its magnitude, an earthquake is also rated by its intensity. This is how strong or how damaging it was to people, buildings and infrastructure in a given area. It is a number calculated from the relative damage and shaking recorded by seismographs, based on a scale of Roman Numerals.
After an earthquake, there are usually many aftershocks that occur. These are smaller earthquakes that strike within the same fault area as the main quake, and can continue for weeks, months and even years!