Thermodynamic constraints on phase changes as earthquake source mechanisms in subduction zones

Application of thermodynamic equations for phase transitions with a shock wave output from metastable to stable phases that are believed to occur in subduction zones indicates that while many show a volume reduction, and thus may contribute to slab pull mechanisms of plate tectonics, they do not satisfy criteria for the generation of shock waves. Of the reactions considered only one (antigorite + clinoenstatite → forsterite + talc) satisfies the criteria, and for this case the shock wave pressure is, in fact, less than the pressure calculated for the leading edge of the subduction zone. This would imply that if the transition does occur under shock conditions in the subduction zone, dilatational rather than compressional first motions for the associated earthquake are expected.