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Earthquakes are tremors or vibrations in the Earth's crust that are caused by the build up or accumulation of pressure (also termed stress) within the Earth's crust.

The Earth's crust is made up of several large areas called tectonic plates. These move in relation to each other, some moving around, over, or under the other plates.

Most earthquakes occur when the plates have been held in place, allowing stress to build up along the boundary where they are in contact (which is called a fault).

This accumulation of stress causes the rocks that make up the crust around the fault to deform elastically. This is very similar to what happens when you squash or stretch a spring and causes a form of energy to be stored in the rocks of the crust - technically described as elastic potential energy.

When this stress gets to large, it exceeds the strength of the rocks in the crust and causes a brittle failure. Brittle failures are failures where fractures form through the material.

This sudden brittle failure causes all of the elastic potential energy to be released at one time in the form of seismic waves, just as if a spring or elastic band that was being stretched suddenly snapped.

These seismic waves travel outward in different directions from the starting point where the energy has been released. An good way to imagine this is to think about what happens when you throw a stone into a pond. This forms concentric circular ripples outwards in a similar way to how seismic waves radiate from the center of the earthquake

These seismic waves cause the tremors that people feel on the surface and which can cause damage to buildings and other structures.

More rarely, quakes can be created or triggered by surface events that create similar motion in the crust : volcanic eruptions, landslides, floods, building collapses, or large man-made explosions.

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12y ago

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