I don't think that either one of those answered your question. The relationship between earthquakes and volcanoes is that when volcanoes are formint, and the volcano is in the active stage of its life, it will experience seismic anomalies (earthquakes) caused by the movement of magma within its chamber and conduits. Any time you have large amounts of rock moving together (which is all that magma is -- just really hot rock, only fluid enough to move), you're going to experience earthquakes. It's in this way that we have gotten pretty good at predicting volcanoes. When a volcano experiences increased seismic activity, it's a sign that magma is moving and shifting, increasing the possibility of eruption. By motoring the magnitude and movement of these earthquakes (using common seismic wave propagation mathematics), we can really zero in with good information, allowing the populace time to move to safe ground. Yes, it's true that tectonically active areas -- the convergent / subduction boundary type -- are related to volcanoes, but that isn't really a relation between an earthquake and volcano. In these cases, the subducting plate melts, new magma is created and rises to the surface as a new volcano (or feeding an existing one). This zone *also* has small earthquakes. However, these are not necessarily directly related to one another. It's the movement within a building or existing volcano of magma that is the direct relationship.