Deep roots of seismotectonics of the Far East: The Amur River and Primorye zones |
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Authors: | A A Stepashko |
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Institution: | 1.Institute of Tectonics and Geophysics, Far East Branch,Russian Academy of Sciences,Khabarovsk,Russia |
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Abstract: | The role of the lateral structure of the lithospheric mantle in the seismotectonics and seismicity of the southern part of
the Russian Far East has been investigated. The positions of the epicenters of all the major earthquakes in Sakhalin (M ≥
6.0), as well as in the Amur region and the Primorye zones (M ≥ 5.0), are defined by the boundaries of the Anyui block of
highly ferruginous mantle, which lies at the base of the Sikhote-Alin area. Three cycles of large earthquakes are recognized
in the region: the end of the 19th-beginning of the 20th century, the mid-20th century, and end of the 20th-beginning of the
21st century. In the seismic zone of the Amur region (hereafter, the Amur seismic zone), the epicenters of the large earthquakes
in each cycle migrate from the SW to NE along the Tan-Lu fault megasystem at a rate of 30–60 km/yr. The specific features
of the seismicity of the region are explained by the repeated arrival of strain waves from the west. The waves propagate in
the upper part of the mantle and provoke the activation of the deep structure of the region. The detailed analysis of the
earthquakes in the Sikhote-Alin area (M ≥ 4.0) in 1973–2009 confirmed the clockwise tectonic rotation of the mantle block.
The characteristics of the Primorye zone of deep-focus seismicity at the Russia-China boundary are stated. Since 1973, 13
earthquakes with M ≥ 6.0 have been recorded in the zone at a depth of 300–500 km. This number of earthquakes is at least twice
as many as the number of large deep-focus earthquakes elsewhere in the Sea of Japan-Sea of Okhotsk transition zone. The unique
genesis of the Primorye seismic zone is related to the additional compression in the seismofocal area due to the creeping
of the Anyui mantle block onto the subduction zone during its rotation. The geodynamic implications of the seismotectonic
analysis are examined, and the necessity of division of the Amur plate into three geodynamically independent lithospheric
blocks is substantiated. |
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