Earthquake swarms are common occurrences in both volcanic and tectonic environments. Swarms and their seismic waves provide a critical window into active processes within the earth, often reflecting the interaction between crustal fluids and earthquake faulting, with dynamic interplay between stress, permeability, and fluid pressure. Swarms of this type exhibit pronounced spatial migration with time, often activating complex fault geometries, likely reflecting the evolution of fluid pressure fronts within a stressed crust. Less well understood are the phase dynamics of the fluids themselves, which in some cases could play an important role in sustaining or even accelerating earthquake swarms.