10:30 AM - 10:45 AM
[J08-3-01] Failed rift system in northern Honshu, Japan, imaged by improved seismic velocity structure using offshore earthquake events
We investigate the 3D seismic velocity structure beneath the ocean using offshore events with seismic tomographic method. Offshore events have a large uncertainty for focal depth determined by NIED Hi-net, however, NIED F-net determined the focal depth with moment tensor inversion. In this study, the data is the combination of the hypocenter catalog by NIED F-net and pick data by NIED Hi-net for offshore events as well as the hypocenter catalog and pick data by NIED Hi-net for events within the seismic network.
The target region, 20–48N and 120–148E, covers the Japanese Islands. The available data for use in the seismic tomography are manually picked 4693781 P-wave and 2342621 S-wave arrival times for 796779 earthquakes recorded at approximately 1300 stations from October 2000 to December 2014. The inversion reduces the RMS of the P-wave traveltime residual from 0.507 s to 0.193 s and that of the S-wave data from 0.609 s to 0.238 s after eight iterations.
Our new analysis clarified the failed rift structures, marked by higher Vp at lower crust and lower Vp at the upper crust, along the Japan Sea cost of central Honshu. Judging from the age of the rift basin, they were produced during the formation of the Japan Sea. Similar, rift structure also detected along the Pacific coast of Northern Honshu, it is marked by uplifted Moho surface, trending NS to NNW-SSE direction. Geologically, it is interpreted as a rift structure formed in the late Mesozoic. Further tectonic investigation for this probable Mesozoic rift is needed. These failed rift zones show similar features in seismic velocity structure and have shallow Moho (Matsubara et al., 2017).
Reference:
Matsubara M., H. Sato, T. Ishiyama, and A. D. Van Horne (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.
The target region, 20–48N and 120–148E, covers the Japanese Islands. The available data for use in the seismic tomography are manually picked 4693781 P-wave and 2342621 S-wave arrival times for 796779 earthquakes recorded at approximately 1300 stations from October 2000 to December 2014. The inversion reduces the RMS of the P-wave traveltime residual from 0.507 s to 0.193 s and that of the S-wave data from 0.609 s to 0.238 s after eight iterations.
Our new analysis clarified the failed rift structures, marked by higher Vp at lower crust and lower Vp at the upper crust, along the Japan Sea cost of central Honshu. Judging from the age of the rift basin, they were produced during the formation of the Japan Sea. Similar, rift structure also detected along the Pacific coast of Northern Honshu, it is marked by uplifted Moho surface, trending NS to NNW-SSE direction. Geologically, it is interpreted as a rift structure formed in the late Mesozoic. Further tectonic investigation for this probable Mesozoic rift is needed. These failed rift zones show similar features in seismic velocity structure and have shallow Moho (Matsubara et al., 2017).
Reference:
Matsubara M., H. Sato, T. Ishiyama, and A. D. Van Horne (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.