Anticrack faulting during the phase transformations of olivine to its denser polymorphs is a principal contender for the mechanism of deep-focus earthquakes. The original work on Mg2GeO4 established that initiation of faulting by this mechanism is not due to brittle fracture and subsequent experiments on olivine of mantle composition showed that it can operate at pressures of at least 14 GPa. Here we report acoustic emissions accompanying anticrack faulting in Mg2GeO4, thereby confirming that this mechanism involves a dynamic instability accompanied by elastic radiation. ¿ American Geophysical Union 1992