The Earth's crust is made up of a number of major and minor tectonic plates which float on a sea of magma (molten rock). Convection currents move the plates over time. Think of scum forming on the top of a bubbling pot of oatmeal. Over time some plates bump against each other and push up (like the Himalayas). Others subduct, dive down, under another plate. The Ring of Fire is a group of plates with are active as seen by the volcanoes (where pressure is being released). Mt. Redoubt is on a different plate than the volcano in Colombia, but when you see increased seismic activity on one part of the Ring, you often see increased activity on another part. If you have an orange and you squeeze it hard enough, eventually it will crack and juice and pulp will spurt out of another place. Check out CalTech's sites on seismic activity. Lawrence Hall of Science in Berkeley also tracks seismic activity.