Double Seismic Zone for Deep Earthquakes in the Izu-Bonin Subduction Zone

A double seismic zone for deep earthquakes was found in the Izu-Bonin region. An analysis of SP-converted phases confirms that the deep seismic zone consists of two layers separated by ~20 kilometers. Numerical modeling of the thermal structure implies that the hypocenters are located along isotherms of 500^circ to 550^circC, which is consistent with the hypothesis that deep earthquakes result from the phase transition of metastable olivine to a high-pressure phase in the subducting slab.