Deep roots of seismotectonics in the Far East: The Sakhalin zone

作者：Stepashko A A^*

来源：Russian Journal of Pacific Geology, 2010, 4(3): 228-241.

DOI：10.1134/S181971401003005X

• seismic activity
• mantle structure
• tectonic extrusion
• deformations
• migration of earthquakes
• Sakhalin Island
• Russian Far East

It is shown that the deep structure of the lithosphere played a decisive role in the recent deformations and seismicity in the Far East. The regional variations in the composition of the mantle xenoliths and Neogene-Quaternary basalts provided grounds for mapping the NE-extending wedge-shaped block of the Fe-rich mantle at the base of Sikhote Alin. Its boundaries continue the Yilan-Yiton and Fushun-Mishan strike-slip faults of the Tan-Lu zone, along which this mantle block was displaced along the continental margin in the Jurassic-Cretaceous. The localization of strong (M a parts per thousand yen 5.0) earthquake epicenters in the Amur region shows that such a mantle structure determines the key features of the regional deformations and seismotectonics. Under the dominant western compression due to the Amur Plate's motion, the mantle wedge is extruded in the northeastern direction to provide an additional stress at the Okhotsk Plate boundary. This process resulted in the formation of the Sakhalin high-seismicity zone at the front of the mantle block. In its characteristics, the zone is similar to the convergence area between the Indian and Eurasian plates. In both cases, the main deformation and seismicity features were caused by the horizontal pressure of the tectonic block, the frontal part of which is marked by regularly alternating compression and extension zones. In Sakhalin, strong earthquakes with M a parts per thousand yen 6.0 are confined to the seismic suture 50 km wide with concentrated compression. This structure is discordant relative to the main faults of the island, being parallel to the front of the mantle wedge. The two migration cycles established for the Sakhalin earthquakes with M a parts per thousand yen 6.0 correspond to periods of 1907-1971 and 1995-2007. During both cycles, the first shocks occurred in the north and subsequently migrated in the southeastern direction simultaneously decreasing in the depths of the earthquake foci. The systematic migration implies that asymmetrical compression is responsible for both the extrusion of the mantle wedge and its southeastward clockwise rotation. The latter plays the decisive role in the initiation of strong earthquakes on Sakhalin.

• 出版日期2010-6