Geodynamics of Modern Structures and Seismotectonics of the Russian Northeast

We conducted an interdisciplinary study of the Arctic, Chersky, and Okhotsk-Chukotka seismic belts, which bound the Kolyma-Chukotka block of the North American plate in Northeast Russia, to determine the stress-strain state of the crust and the types of seismic deformation therein. The rank and class of neotectonic structures was based on their degrees of geodynamic activity, structural position, deep structure, and their active fault systems. The tectonic stress field was determined from Late Cenozoic faults and folds and average seismic moment tensors from earthquake focal mechanisms. Using geological, structural, geophysical and GPS data and average strain tensors, we determined the directions of the principal stress axes and the variation of tectonic settings in the Russian Northeast. Within the boundary zones between the Kolyma-Chukotka block and the Eurasian, Bering Sea and Pacific plates, the geodynamic settings change from one segment to another as follows: the crust is under extension in the Gakkel Ridge segment (Arctic belt) as the lithospheric plates diverge; the Laptev Sea shelf and Kharaulakh segments comprise a transitional zone with mixed stresses; in the Chersky seismic belt, left-lateral strike-slip faulting occurs from northeast compression due to the oblique convergence of the North American and Eurasian plates; in the Commander and Aleutian Islands segment, right-lateral strike-slip faulting is caused by the northwestward convergence and higher relative velocity of the Pacific plate; the crust is under compression due to convergence with the Bering Sea plate in the Koryak segment (Okhotsk-Chukotka seismic belt), resulting in systems of reverse, thrust and right-lateral strike-slip faults. To the northeast, this transitions into the extension of the Bering Sea rift. The seismotectonic data from the active boundaries of the Kolyma-Chukotka block are consistent with the distribution and types of observed structural features in each belt and segment. This supports the geodynamic model for the causes and development of the main seismogenic structures in the Russian Northeast as due to plate interactions in the Pacific - North America - Eurasian plate boundary region.