Role of shallow phase changes in the subduction of oceanic crust.

Detailed studies of the seismicity of several subduction zones demonstrate that shallow-dipping thrust zones turn to steeper angles at depths of about 40 kilometers. An increased downward body force resulting from shallow phase changes in subducted oceanic crust may be the cause of this increased dip angle. In addition, the volume reduction associated with phase changes may produce sufficiently large stresses in neighboring rocks to cause the seismicity of the upper Benioff zone.