sentences:  They propose that transformational faulting, which occurs when metastable olivine changes to a more compact spinel structure, produces this zone of seismicity.Indeed, the faulting mechanism for deep earthquakes is a hotly debated topic (e.g., ), and has yet to be resolved.Double seismic zones (DSZs) have been detected in several parts of the IBM subduction zone, but their locations within the slab as well as interpretations for their existence vary dramatically.