  Deep-focus earthquakes that occur at 350-660 km are theorized to be caused by
strain-induced olivine-spinel phase transformation (PT). We introduce and apply
dynamic rotational diamond anvil cell with rough diamond anvils to deform San
Carlos olivine. While olivine was never transformed to spinel at any pressure
at room temperature, we obtained olivine-ringwoodite PT under severe plastic
shear at 15-28 GPa within seconds. This is conceptual proof of the difference
between pressure- and plastic strain-induced PTs and that plastic straining can
accelerate this PT from million years to timescales relevant for the
earthquake. The PT pressure linearly reduces with increasing plastic strain,
corresponding increasing dislocation density and decreasing crystallite size.
The main rules of the coupled severe plastic flow, PT, and microstructure
evolution are found.
