While metamorphic reactions in the subducting slab liberate large amounts of fluids, low-frequency earthquakes (LFE) largely occur beneath impermeable unmetamorphosed overlying plate, and are rare beneath metamorphosed plate. Scientists suggest that undrained conditions are a key factor in the generation of LFEs, whereas well-drained conditions reduce pore-fluid pressures at the megathrust and inhibit LFEs and associated tremors.