Short-period Full Waveform Modeling of the Spatial Relationships of Fine Slab Structure and Deep Earthquakes beneath Japan and Izu-Bonin

Despite increasingly improved tomography resolution, fine slab structure such as the low wave speed (low-V) oceanic crust and possibly low-V serpentinized slab mantle are not yet resolved in 3D regional tomographic models. Direct imaging of the deep slab surface and other interfaces within the slab are limited along only a few profiles using receiver functions, and it is a common practice in geophysical studies to determine the slab upper interface by interpolating shallow and deep-focus earthquake hypocenters. This poses challenges to inferring the mechanisms of intermediate and deep-focus earthquakes, for which accurately establishing the spatial relationships of deep earthquake location and slab structure is essential. A previous full waveform inversion model FWEA18 shows promising results of capturing slab geometry from intermediate-period seismic waveforms (periods of 8 s and longer) independently from deep seismicity. This study builds upon model FWEA18 and aims at improving the fine slab structure and deep earthquake location by incorporating shorter period body waves (to the shortest period of 5 s), which travel through the Japan and Izu-Bonin Subduction Zones. Our data set includes waveforms of 192 regional earthquakes at different depths recorded by 345 stations in Japan, NE China and South Korea. This study applies full waveform modeling based on a spectral-element method and focuses on the body waves strongly diffracted by the high wave speed slab, low-V mantle wedge, and possibly low-V waveguides within the slab, which may indicate the hydrous slab layers or metastable olivine wedge.