You should be aware that whilst most volcanoes / earthquakes occur along plate boundaries, there are exceptions. For example the volcanic Hawaiian islands which can be found in the middle of the Pacific Plate are formed due to a hotspot. Hotspots are plumes of molten rock which rise underneath a plate causing localised melting and the creation of magma resulting in volcanic activity. This animation explains the formation of a hotspot and associated landforms very well.
The map below shows the location of volcanic hotspots.
A map to show volcanic hotspots