Individual plates of varying size move about the surface of the Earth at varying speeds. Where plate pull apart, slide by each other or collide, there is tectonic activity manifested as earthquakes. The great majority of seismicity on the planet occurs at plate boundaries, although intra-plate seismicity can occur as well when stresses build up in the plate.
Volcanism can also occur at intraplate volcanoes.
These volcanoes are believed to have sources deeper down in the Earth's mantle that remain in a relatively fixed location relative to the always migrating plate boundaries. Mauna Loa and Kilauea in Hawaii are the classic examples of intraplate volcanoes. Such volcanoes can also be seismically active, particularly when volcanic structures are built up rapidly. The crust must respond to the extra load and relieves this stress through tectonic activity.