俄罗斯贝加尔湖-日本仙台断面地震波速结构及其地质意义

本文以中俄、俄日学者合作所得到的地球物理资料为主,结合其它相关地质-地球物理数据,组构了俄罗斯贝加尔湖-日本仙台(BS)4000 km长断面,用于区域性大尺度地研究东北亚洲地壳结构和一系列地质构造问题.研究BS断面地震波速结果表明:(1)西伯利亚板块和黑龙江板块地壳结构变化较大,并可分为上、中、下部地壳,欧亚板块东部陆缘带地壳结构较简单,基本两分.贝加尔裂谷带下部地壳厚度比松辽盆地的薄约7 km,而上部地壳则相反,前者的比后者的厚约9 km.两个裂谷带在Moho界面之下的波速分布差异也较大.(2)结合前人认识,综合分析认为,贝加尔裂谷带属主动式裂谷,松辽盆地属于混合型裂谷.贝加尔裂谷形成动力主要来自地球构造圈B″层物质上涌所形成的地幔热柱的垂向作用,由BLV带佐证,松辽盆地形成动力主要来自太平洋板块斜向俯冲的中远程效应.(3)日本国所位于的西太平洋岛弧带是多地震带,除了太平洋板块俯冲产生的浅部效应、地壳中断裂与流体的直接作用等因素,本文指出仙台等速块的物性条件是岛弧带的主要不稳定因素.同时指出需要关注日本东海岸深约30~40 km的大级次地震的发生.

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 30~40 km.