Fig. 5. Schematic showing fluid migration paths between the sources and sinks of water in the Hellenic subduction zone.

The fluids originate from dehydration reactions in the slab and flow either toward the melting zone in the mantle or updip below a sealed plate interface. Fluids that flow updip trigger earthquakes (EQ; black circles) as they migrate along the slab toward the overriding crust (where they precipitate into quartz) or if they escape via localized vents into the cold mantle wedge corner (where they cause unusual mantle wedge earthquakes). Reduced fluid flow in the subducting crust updip of these vents leads to reduced seismicity. Other subduction zones with cold interfaces and dry mantle wedges (see Fig. 4) exhibit similar fluid migration patterns.