Seismic wave velocity structure of the Russia Baikal Lake-Japan Sendai transect and its geological implications

Based mainly upon the geophysical data from the cooperation between Chinese-Russian and Russian-Japanese scientists, and in combination with other related geological and geophysical data, this work studies the crustal structure along the 4000 km-long Russia Baikal Lake-Japan Sendai (BS) transect and a series geological problems in northeastern Asia. The results of the study on seismic wave velocity along the transect indicate that the crustal structure of the Siberia plate and Heilongjiang plate change much laterally and can be divided into upper, middle and lower crust. The crustal structure of the eastern continental margin of the Eurasian plate is simple which can be divided into two layers. The thickness of the crust beneath the Baikal rift zone is thinner about 7 km than the Songliao basin, opposite for the upper crust, the Baikal rift zone is more thicker by about 9 km. There is a big velocity distribution difference between two rift basins around the Moho interface. Combining existing results, we suggest that the Baikal rift zone is an active rift basin and Songliao basin is a composite rift. The dynamic force of Baikal rift' formation came from the vertical effect of thermal mantle plum from the Earth's layer B", as evidenced by BLV. The middle and long distance effects of the Pacific plate oblique subduction can explain the development of the Songliao. The western Pacific island arc at which Japan is located is a seismically very active region. This article suggests that the physical properties of the Sendai constant velocity block are the main factors for instability of the island arc zone in addition to the shallow effect produced by Pacific plate subduction and the direct interaction between faults and fluid in the crust. At the same time, we need to concern about the potential large magnitude earthquakes around the eastern beach of Japan at depths 30 similar to 40 km.