Abstract
One of hypotheses for deep earthquake generation is a phase change hypothesis. In order to examine this possibility, we studied the reaction rate for the phase change from nickel olivine (Ni2SiO4) to nickel spinel (Ni2SiO4) under high pressure and high temperature by the use of tetrahedral press.
The reaction rate is expressed by the equation: dX/dt=K(1-X)P, where K is the rate constants, X is the amount of product, t is time and p is the order of reaction. The rate constant K is given by the equation: K=K0(KT/h) exp (-ΔAE/kt)sinh(αΔP/KT), where K0 is a constant, T is the absolute temperature, k is the Boltzman constant, h is Plank's constant, ΔE is the activation energy, ΔP is the deviation of pressure from the eqgilibrium state and α is a constant. If (αΔP/kT)<<1, the above equation becomes K=K0(αΔP/h) exp (-ΔE/kT).
We obtained such a result that if the phase change of olivine-spinel was a first order reaction in terms of reaction kinetics, the rate constants K for 800°C, 40kb, for 900°C, 40kb and for 1000°C, 40kb became 10-3/min., 6×10-3/min. and 2.3×10-1/min. respectively.
Based on the above equation and experimental results, we obtained the result that when ΔP=1kb and T=1300°C, 80 percent olivine would be converted into spinel within 15 seconds. This rate of phase change seems to be so rapid as to cause an earthquake.
