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[S21-P-10] Shallow Moho along the failed rift on the coast of Japan Sea beneath Japanese Islands
The Mohorovicic discontinuity (Moho) is defined on the basis of an abrupt increase in seismic velocity within the lithosphere observed using seismic refraction and receiver function analysis methods worldwide. Moho depth varies regionally and remains a fundamental parameter of crustal structure. This study presents a new method of mapping the Moho using a 3D seismic tomography model. A zone of high velocity gradient is treated as the Moho because the tomographic method cannot clarify discontinuities.
Maximum lower crust/minimum upper mantle P-wave velocities in Japan are known to be 7.0 km/s and 7.5 km/s, respectively. The small residual between isovelocity surfaces of 7.0 km/s and 7.5 km/s corresponds to the high velocity gradient. The best constrained Moho is where the isovelocity surfaces are close together, and under much of Japan, the residual is less than 6 km and rarely larger than 10 km apart. We selected an isovelocity surface of 7.2 km/s as a representative Moho ‘proxy' beneath Japanese Islands. Our resulting Moho map beneath Japan is consistent with existing regional Moho models that were obtained by controlled-source seismic investigations.
The Moho varies from shallow (25-30 km) to deep (> 30 km), and this variability is related to the structural evolution of the Japanese islands: the opening of the Sea of Japan back-arc, ongoing arc-arc collisions at the Hidaka and Izu collision zones, ongoing back-arc extension in Kyushu, and a possible failed back-arc extensional event of Mesozoic age (Matsubara et al., 2017). The Moho along the failed rifts on the Japan Sea side beneath the central Honshu Island is shallow since the high-V lower crust exists there.
Reference:
Matsubara et al. (2017) Configuration of the Moho discontinuity beneath the Japanese Islands derived from three-dimensional seismic tomography, Tectonophysics, in press, doi:10.1016/j.tecto.2016.11.025.
Maximum lower crust/minimum upper mantle P-wave velocities in Japan are known to be 7.0 km/s and 7.5 km/s, respectively. The small residual between isovelocity surfaces of 7.0 km/s and 7.5 km/s corresponds to the high velocity gradient. The best constrained Moho is where the isovelocity surfaces are close together, and under much of Japan, the residual is less than 6 km and rarely larger than 10 km apart. We selected an isovelocity surface of 7.2 km/s as a representative Moho ‘proxy' beneath Japanese Islands. Our resulting Moho map beneath Japan is consistent with existing regional Moho models that were obtained by controlled-source seismic investigations.
The Moho varies from shallow (25-30 km) to deep (> 30 km), and this variability is related to the structural evolution of the Japanese islands: the opening of the Sea of Japan back-arc, ongoing arc-arc collisions at the Hidaka and Izu collision zones, ongoing back-arc extension in Kyushu, and a possible failed back-arc extensional event of Mesozoic age (Matsubara et al., 2017). The Moho along the failed rifts on the Japan Sea side beneath the central Honshu Island is shallow since the high-V lower crust exists there.
Reference:
Matsubara et al. (2017) Configuration of the Moho discontinuity beneath the Japanese Islands derived from three-dimensional seismic tomography, Tectonophysics, in press, doi:10.1016/j.tecto.2016.11.025.