Theoretical mineralogy, density, seismic wavespeeds and H2O content of the Cascadia subduction zone, with implications for intermediate-depth seismicity and earthquake hazard

We calculate physical properties of rocks in subduction zones using a compilation of mineral physical property measurements, a new set of phase diagrams and subduction-zone thermal models, and apply our results to Cascadia. Observed P-wave speeds of the Juan de Fuca plate west of the Cascadia trench are best matched by a greenschist-facies upper crust and metastable, partially hydrated lower crust and mantle. The predicted positions of dehydration reactions in the subducting crust show a spatial link to observed seismicity, suggesting that dehydration may be the cause of the earthquakes and that the predicted location of dehydration reactions in the slab can be used to predict hazardous seismicity the length of