What do tectonic plates have to do with earthquakes?
The earth s surface is made up of 15 huge, rigid plates of rock anywhere from 15 km to 100 km thick. These plates are constantly moving and at their edges they are constantly bumping and grinding into each other. The constant movement causes stresses to build up in the brittle, upper layers of the plates. When the brittle rock finally breaks, it generates an earthquake. Plates, such as the Pacific plate, that carry a limited amount of land mass move the fastest. Under New Zealand, the Pacific plate is moving at about 50 mm a year about the same rate that your fingernails grow. The entire plate interaction zone is potentially a source of moderate to large earthquakes. The rim of the Pacific Ocean, where the Pacific plate sinks under or slides past other plates, is one of the most active of all the earth s plate boundaries. Plates don t jostle haphazardly they move only in one direction, at least in the short geological time frame.
