Explosive Phase Transitions in the Earth's Mantle

Abstract

THE Earth's crust and mantle deform viscoelastically. There has, therefore, been some question as to whether stress relaxation rates in the upper mantle and lower crust might not exceed any realistic rates of stress accumulation. If this is so, earthquakes could not be generated by rebound of elastic strain; that is, by either the type I or type II source of Honda¹. It might, therefore, be worth-while to explore the possibility of an earthquake mechanism in which stress is suddenly applied rather than suddenly released. One such mechanism is a phase transition, quasi-instantaneous over a finite volume and involving lattice condensation. Recent experiences with underground nuclear explosions² have shown that explosive strain may release an adequate portion of energy in the form of S waves, so that observed radiation patterns may well be accounted for by an explosive (or implosive) phase transition.