How are earthquakes formed by plate tectonics?

Answer 1

Earthquakes are caused by the build up or accumulation of pressure (more correctly termed stress when it an internal result of strain) due to the collision or interaction of the tectonic plates that form the Earth's lithosphere.

This accumulation of stress causes the rocks that make up the crust 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.

Answer 2

Earthquakes are formed by the movement of tectonic plates. When these plates grind against each other, tension builds up until it is suddenly released in the form of seismic waves, causing the ground to shake. This can occur at plate boundaries, such as subduction zones or transform faults.