Evolution of the Downgoing Lithosphere and the Mechanisms of Deep Focus Earthquakes

The thermal evolution of the lithospheric slab at subduction zones and its geophysical effects are numerically calculated. An alternating-direction, implicit, finite-difference scheme is used to compute the thermal models taking into account all heating sources and phase boundaries. These models, with the appropriate spreading rates and dip angles, are compared with different island arc systems. Temperatures inside the slab are strongly controlled by the conductivity and by the time elapsed since the initiation of descent. The depth to which temperature anomalies persist is generally about 700 km or less.