The rigid continental crust is not moving through an equally rigid oceanic crust. Instead, the two types of crust are attached and the two types together are floating on the mobile asthenosphere and are moving away from the midocean ridges. There are seven major plates in the world and several smaller ones. At divergent boundaries the plates are pulling apart and new oceanic crustal rocks are created in the gap by upwelling of magma from the mantle. At convergent boundaries the subducting plate melts as it descends into the mantle and the rising magma forms chains of volcanoes and batholithic intrusions parallel to the subduction zones.
Convergent boundaries are faults.
At transform boundaries the plates move laterally past one another between two offset divergent plate boundaries. Like convergent plate boundaries, transform boundaries are faults. The plates move past one another only between the offset divergent plate boundaries. Beyond the area of the offset, the plates move the same direction and at the same speed. Earthquakes should be most abundant in places where plates are subducting or scraping past one another and there should be a systematic relationship between the focus of the earthquake and its depth.