Final answer:
At plate boundaries, earthquakes are caused by the build-up and release of stress in the crust. The motion of the plates against each other creates stress that is eventually released in sudden slippages, resulting in earthquakes.
Step-by-step explanation:
In plate boundaries, earthquakes are caused by the build-up and release of stress in the crust. The creeping motion of the plates against each other creates stress that is eventually released in sudden slippages, resulting in earthquakes.
The longer the interval between earthquakes, the greater the stress buildup and the more energy is released when the surface finally moves. This is because the average motion of the plates is constant.
For example, at convergent boundaries where one plate subducts under another, the stress from the collision builds up until it is released in a large earthquake. Similarly, at transform boundaries where plates slide alongside each other, stress accumulates until it is released in a sudden slippage, causing an earthquake.