An earthquake swarm is what it sounds like: a lot of earthquakes rumbling across a fault system over a short period of time. The phenomenon is helping researchers uncover the link between sinking tectonic plates and volcanoes.

Recently, researchers discovered a pair of earthquake swarms while surveying the Pacific Ocean's Mariana and Izu-Bonin arc systems. When scientists mapped the swarms' seismic signatures in 3D, they discovered a pipeline of sorts linking the sinking tectonic plates and a pair of magma chambers.

The discovery -- described this week in the journal Earth and Planetary Science Letters -- explains how volcanoes receive molten rock from tectonic activity.

The Mariana and Izu-Bonin arc systems are found along the boundary of two tectonic plates, the Philippine Sea Plate and the Pacific Plate. As the Pacific Plate sinks beneath Earth's mantle, it carries water deep beneath the planet's crust. As the water gets deeper and deeper, the heat and pressure causes the water to become superheated. When it tries to escape, rocks fracture and melt, creating a pipeline through which molten rock can rise.

"In fracking used by the petroleum industry, they drill into the Earth up to a few kilometers deep, and then continue to pump liquid down until the pressure grows and the rocks crack, creating a path for the petroleum or natural gas to flow through the rocks and into a pipe back to the surface," Lloyd White, earth scientist at University of Wollongong in Australia, said in a news release. "In this case, the tectonic plate carries the water down very deep into the Earth, down to around 200 kilometers below the surface. As the plate goes down it gets hotter and the pressure gets higher, driving water out of subducted plate."

The new research suggests the subducted water causes rock to fracture and melt, creating the magma itself, as well as to create a path through which the molten rock can travel. The activity also generates a series of small earthquakes, or earthquake swarms.

"It is similar to fracking, but at a much grander scale and completely driven by Earth's natural processes, rather than being human induced," White said.

Researchers estimate the seismic activity is generated either by the fracturing of rock as superheated water escapes, or as the pipeline collapses once the molten rock has migrated through.

"Geologists have always assumed that the water in this system goes upwards, but we've never had a good way of imaging that," White said. "These examples -- a freak occurrence that we've stumbled on -- show very clearly where the water must be traveling."

The new research could help scientists identify the volcanoes that are being supplied with large amounts of molten rock, and are therefore at a greater risk of erupting.

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