Most plates consist of both continental and oceanic crust. Plates move away from each other at spreading centers (divergent boundaries). A convergent plate boundary separates plates that are moving toward each other. A transform plate boundary is a fault zone along which two plates slide in opposite directions. Oceanic crust is subducted underneath continents or in oceanic trenches. Continental crust is less dense than oceanic crust and therefore will not subduct because it is lighter.
Compared to its edges, a plate's interior is relatively stable, with few earthquakes and little igneous activity or structural deformation. Flood basalts and mantle plume “hot spots” have been known to occur in the interior, but the majority of seismic, volcanic, and mountain‐building activity occurs along a plate's boundaries (Figure 1), including frequent earthquakes.