 The recording of several years of background seismic data has allowed for classification of volcanic earthquakes.These earthquakes tend to occur in swarms as opposed to mainshock-aftershock sequences, have smaller maximum sizes than tectonic structure earthquakes, have similar waveform patterns, increase in number before eruptions, and occur near or beneath the size of the eruption.Other types of seismic activity to monitor related to volcanoes and their eruptions are long period seismic waves, which are caused by sudden sporadic movement of magma, that had previously not been moving due to a blockage and harmonic tremors, which are steady movements of magma, deep in the mantle.