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Massive M > 8 earthquakes have repeatedly struck the coastal Chilean subduction megathrust at intervals of nearly ten years, and such tsunamigenic earthquakes have caused recurrent damage. A widely accepted mature seismic gap along the strongly coupled plate interface in northern Chile was filled unexpectedly by the occurrence of the 2014 M-w 8.2 Iquique earthquake, which occurred 130 years after the previous quake. This event revealed that our understanding of the state of seismogenesis along the Chilean margin is still poor. This study aims at investigating the temperature and water content distributions within the Nazca slab along a large portion of the Chilean margin. We employ 3-D time-dependent thermomechanical numerical models that incorporate up-to-date slab geometry and phase diagrams of hydrous minerals in the subducting plate to study the north central Chilean (19 degrees S-33 degrees S) coupled megathrust, including the region where the slab is subhorizontal (28 degrees S-32 degrees S). Our modeling results show that most shallow off- and onshore interplate earthquakes in north central Chile in the last decade have been mainly controlled by the phase transformation from lawsonite blueschist to amphibolite at shallow depths. On the other hand, some of the deep subduction seismicity is in good agreement with eclogitization within the oceanic crust and formation of harzburgite in the ultramafic rock in the lower slab. The M > 6 interplate earthquakes are estimated to occur where our models predict slab temperatures less than 400-600 degrees C and slab dehydration less than 0.03-0.05 wt%/km. Slow slip events tend to occur in regions where interplate temperatures are 400-600 degrees C (0.03-0.05 wt%/km). The activity level of regional interplate earthquakes and slow slip events is interpreted to be affected by the fluid release from and the temperature distribution in the Nazca slab.