Characterized by repeated large earthquakes, slow slips, and tectonic tremors with their simultaneous release of large amounts of energy, the unstable subduction interface beneath Alaska presents a chance to understand the composite dynamic transition from deep to shallow subduction channel where these enigmatic fault slips and seismic events occur. The complex subducted slab morphology associated with the frequent occurrence of various types of faulting behaviors in Alaska is poorly understood. Our result shows that the subduction of the Pacific plate and the subsequent release of large amounts of fluid likely contribute to the repeated fast and slow earthquakes there, as evidenced by the petrological metamorphic transition in the incoming plate. The offshore Alaska seismogenic zone, as well as the slow earthquakes identified near the Upper Cook Inlet, compare well with the distribution of slab dehydration slivers, including large destructive earthquakes that have occurred in Alaska. The fluid upwelling from dewatered oceanic crust and the continental wedge serpentinizing is probably related to various transportation pathways controlled by dip angle and upwell in the predominant direction following the subduction channel or veins in the overriding lithosphere.