Fig. 2

a, b Panels showing histogram of earthquakes in crust and mantle for cold and warm subduction zones (modified from Abers et al. 2013). c Figure showing H\(_2\)O carrying capacity in the oceanic crust (modified from Hacker 2008). The P-T paths at the top of the crust and oceanic Moho from Fig. 1c are overlain—bold blue line shows the relevant “blueschist-out” boundary. d Earthquakes limited by “blueschist-out” below Tohoku with interpreted fluid flow (modified from van Keken et al. 2012). e Low \({V_p}\) in crust below Tohoku suggesting presence of free fluids (modified from Shiina et al. 2013). Note that the blue colors in the legend are accidentally rendered as purple in the figure such that the purple region has \({V_p}>\)8 km/s. f Figure showing fluid flow rises primarily with gravity if compaction pressure is ignored (left frame); if it is included (right frame) the fluids tend to be contained in the crust before leaving the slab below the arc (modified from Wilson et al. 2014) similar to the flow of fluids suggested from the seismicity (frame d) and low P-wave velocities (frame e)