THE RHEOLOGY OF FAULTS TRIGGERED BY THE OLIVINE SPINEL TRANSFORMATIONIN MG2GEO4 AND ITS IMPLICATIONS FOR THE MECHANISM OF DEEP-FOCUS EARTHQUAKES

The relevance of the anticrack faulting mechanism to the origin of dee p-focus earthquakes depends critically on the physical processes opera ting during fault generation and movement. We show here that the resis tance to sliding on fault zones produced by this mechanism in Mg2GeO4 depends only weakly on confining pressure, but strongly on sliding rat e. Both of these characteristics are inconsistent with friction. The m icrostructures of the fault zones and the crystal-plastic rheology of the constituent phases indicate that sliding must occur primarily by g rain-boundary sliding. Previously, we reported that anticrack faulting is accompanied by elastic radiation of energy (ar-oustic emissions), and that it can operate during the alpha --> beta transformation in (M g,Fe)2SiO4 at the pressures and temperatures at which deep earthquakes occur. The present results and the recent demonstration that metastab le olivine is present in the subducting slab beneath Japan provide add itional support for the anticrack theory of deep-focus earthquakes.