[S-CG49] 島弧の構造・進化・変形とプレート沈み込み作用

[SCG49-07] 3-D Crustal Shear Wave Velocity Model Derived from the Adjoint Tomography in the Central Japan

*椋本 浩太¹、辻 健¹ (1.九州大学)

キーワード：アドジョイントトモグラフィー、波形インバージョン、S波速度構造

In Japan, most seismic velocity models for crust structure investigation have been estimated by ray tomography. This method has resolved the many interesting geological features related to the fluids, volcanic activities, earthquake faults, and interactions of the plates. The adjoint tomography that takes the advantage of full numerical seismic wave simulation and banana-doughnut sensitivity kernels has led to more accurate estimation and fine structures in the crustal and global seismic tomographic model. However, applications of the full waveform inversion have been limited. In this study, we estimated 3-D crustal S-wave velocity model based on the adjoint tomography in the Central Japan Island. The waveforms of 70 earthquakes were collected from 385 3-components high sensitivity seismometers (Hi-net). The phase shift between observed and synthetic seismograms filtered over the period range 10-30 sec was minimized by successively updating the velocity models from the initial model. After 21 iterations, the phase misfit was reduced by 11.3%. The estimated S-wave velocity model revealed the distinct low- and high-velocity anomalies related to the magmatic fluids, sedimentary basins, volcanoes, and lithologies. Based on the waveform comparisons between before and after the inversion, minimizing the phase misfit improves not only the phase misfit but also the amplitude differences. This means the constructive and destructive interference of the seismic wavefields was also improved. The first S-wave velocity model by applying the adjoint tomography to the Hi-net stations suggests the applicability of the waveform inversion to the Hi-net stations in Japan and opportunities to image heterogeneous crustal structures in the Japan Island.