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Seismic evidence for a metastable olivine wedge in the subducting Pacific slab under Japan Sea
Authors:Guoming Jiang  Dapeng Zhao  Guibin Zhang
Institution:aDepartment of Geophysics, Tohoku University, Sendai 980-8578, Japan;bSchool of Geophysics and Information Technology, China University of Geosciences, Beijing, China
Abstract:We apply a forward-modeling approach to high-quality arrival time data from 23 deep earthquakes greater than 400 km depth to investigate the detailed structure of the subducting Pacific slab beneath the Japan Sea. Our results show that a finger-like anomaly exists within the subducting Pacific slab below 400 km depth, which has a P-wave velocity 5% lower than the surrounding slab velocity (or 3% lower than that of the normal mantle), suggesting the existence of a metastable olivine wedge (MOW) in the slab. The MOW top and bottom depths are 400 and 560 km, respectively. The MOW is estimated to be about 50 km wide at 400 km depth and close to the slab upper boundary. At 560 km depth the MOW is located at about 25 km below the slab upper boundary. Most of the deep earthquakes are located in the MOW. Our results favor transformational faulting as the mechanism for deep earthquakes.
Keywords:metastable olivine wedge  forward modeling  deep earthquakes  Pacific slab  transformational faulting
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