Boris M. Koz'min

Seismicity of the Bering Strait region: Evidence for a Bering block

Newly compiled Russian and U.S. seismological data support an independent Bering block in motion relative to the North American plate. This motion is likely to be driven by the westward extrusion of southwestern Alaska, resulting from compression in southern Alaska due to subduction of the Pacific plate and terrane accretion. Seismicity extends from central Alaska, through the Bering Strait, and into Chukotka. In eastern Chukotka several southwest trends are evident, some of which continue through the Koryak Highlands to Kamchatka. The seismicity outlines the Bering block, which includes most of the Bering Sea, Chukchi Peninsula, Seward Peninsula, and parts of western Alaska. Focal mechanisms, young basaltic volcanism, and normal faults in western Alaska and Chukotka indicate that the Bering Strait is under northeast-southwest extension. This, in conjunction with thrust faulting in the Koryak Highlands, indicates that the Bering block is rotating clockwise relative to the North American plate.

Extrusion tectonics of the Okhotsk Plate, northeast Asia

Based on focal mechanism, geologic, and lineament data, faulting in the Chersky Range, northeast Asia, changes from right-lateral transpression between North America and Eurasia to left-lateral strike-slip between North America and the Okhotsk plate. The location of the Okhotsk-Eurasia boundary is poorly constrained; available data suggest this boundary is right-lateral. The Okhotsk plate is being compressed and extruded from between North America and Eurasia resulting in high levels of microseismic activity along the southern flanks of the Chersky Range.

Cooperative program helps decipher tectonics of northeastern Russia

Recently obtained paleomagnetic, geochronologic, and seismic data are greatly improving our understanding of the tectonics of northeastern Russia, which lies in an accretionary zone between the stable platforms of the North American and Eurasian plates. In particular, the present-day plate boundaries and motions have been clarified and a model has been developed for the accretionary history of the poorly understood Mesozoic fold belts of northeastern Russia. The evolution of northeastern Russia appears to be similar to that of Alaska and the Canadian Cordillera, and many similar tectonic and stratigraphic features can be identified in all three regions.

Explosion Contamination of the Northeast Siberian Seismicity Catalog: Implications for Natural Earthquake Distributions and the Location of the Tanlu Fault in Russia

Russian regional seismicity catalogs, including those in the annual “Earthquakes of the USSR,” are contaminated by industrial explosions. In northeastern Russia, explosions occur in tin, coal, and gold mines, as well as in the construction of roads, railways, and dams. Most seismically recorded mining- and construction-related explosions have magnitudes of about 2.0 and occur during local daytime. In addition, explosions in placer mining areas are concentrated from midwinter to early spring, when frozen placers are broken up for the summer processing season. We analyzed the temporal variation of over 87,000 events occurring in northeast Russia using a newly compiled seismicity catalog to identify areas where there may be explosion contamination. Areas with temporal biases indicative of mining or other explosions include the Yana River delta and Chukotka (placers), the southern Amur district (coal mining), the trace of the Baikal–Amur railroad (construction), Lazo (quarry), the south Yakutian gold fields, and the Kolyma gold belt. The locations, and estimates of the level, of explosion contamination of the catalog suggest that the natural seismicity may be lower, and not as diffuse, along the plate boundaries in northeastern Russia than previously thought. Use of only nighttime events from the seismicity catalog, which should have a minimum of explosions, helps to clarify the extension of the Tanlu fault into Russia and may ultimately help elaborate tectonics in other areas of eastern Russia.

Source parameters of the Taimyr earthquake of June 9, 1990

The results of calculation of the seismic moment tensor (in the double-couple approximation) for the earthquake that occurred in the northeastern Taimyr Peninsula on June 9, 1990, from amplitude spectra of the surface waves, are presented. The obtained results are of interest for works related to construction of geodynamic models for the Taimyr region, for studies of the stress-strain state of the Earth’s crust, and for assessments of the seismic hazard of this territory.

Transpressional structures of the eastern segment of Aldan-Stanovoi block

According to seismotectonic analysis, the territory of the AldanoStanovoi block is the least understood, and, actually, it has not been studied with the use of structuralkinematic models of the modern tectonic process. Analysis of the geological-geophysical char� acteristics of active faults, morphotectonic peculiari� ties of relief, the data set of satellite measurements, and seismic activity made it possible to determine the kinematic plan of development of modern faultblock structures and determine the systems of the main seis� mogenerating faults, located in the contact zone of dynamic affection of three large lithosphere plates: Eurasian, Amur, and Okhotomorsk.