The whole oceanic crust can be replaced in about 100 million years. When one plate slides under another one a subduction zone is created. The thicker continental plates are usually not subducted, in most cases the oceanic plates are driven beneath the continental plates. The subducted plate is forced down into regions of high pressure and temperature allowing the plate to melt. The amount of material destroyed at subduction zones is about equal to the amount of material created at rift zones.
Volcanoes usually lie along the subduction zone.
Faults are places where the plates slide past one another. This sliding motion is about several cm per year. This continental sliding does not occur smoothly. The motion can build up stresses that are then violently released producing earthquakes. The longer the interval between earthquakes the greater the stresses released.