K. Mackey

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.

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.

Crustal thickness of northeast Russia

Abstract The first-order crustal structure of the Magadan region and northeast Sakha Republic (Yakutia), northeast Russia, is obtained by simultaneously inverting for origin times and travel time curves. A total of 1210 observations are used. As an average, a 37-km-thick, 5.992±0.007 km/s crust overlying an 7.961±0.015 km/s mantle provides an excellent fit to phase data listed in the Materialy po Seismichnosti Sibiri bulletin. Travel time curves for individual stations are very close to this average, though there are variations in both crustal thickness and velocities; upper mantle velocities and crustal thickness appear to increase along the southern edge of the Okhotsk-Chukotka volcanic belt, and decrease in the upper Kolyma River basin and along the trace of the proposed Moma rift. Crustal thickness is greatest at Khandyga, on the Siberian platform, and lowest at Yubileniya, which may lie within the currently active Laptev Sea rift system.

Structural dynamic analysis of the epicentral zone of the Ilin-Tas earthquake (Feb 14, 2013, Ms = 6.9)

The paper presents the results of analysis of tectonics, modern relief morphology, active faults, and types of Cenozoic deformations in the epicentral area of the Ilin-Tas (Ms = 6.9) earthquake, one of the strongest events registered at the boundary of the Eurasian and North American lithospheric plates in northeast Russia. Geological, tectonic, and geophysical characteristics of the Yana-Indigirka segment of the Chersky seismotectonic zone are studied. The methods of investigation were elaborated at the Institute of the Earth’s Physics, RAS (Moscow), and were adapted to conducting seismotectonic work on the territory of northeast Russia. The results of instrumental observations are summarized, and manifestations of strong seismic events are discussed. Description is given of the structural–tectonic setting in which the Andrei-Tas seismic maximum developed. It originated under the effect of the Kolyma-Omolon terrane (indentor) which “intruded” into the Chersky seismotectonic zone on the side of the North American plate, thus leading to the formation of major seismoactive structures in the frontal Ilin-Tas folded zone. The indentor moved in NE-SW direction, which is consistent with the orientation of the major axis of isoseism ellipses (azimuth 50–85°) constructed from observation of macroseismic effects of the Uyandina (Ms = 5.6), Andrei-Tas (Ms = 6.1), and Ilin-Tas (Ms = 6.9) earthquakes.

Ground Truth Determinations of Detonation Sites of Peaceful Nuclear Explosions in the Sakha Republic (Yakutia), Russia

Abstract Although ground truth (GT) locations for peaceful nuclear explosions (PNEs) conducted in the former Soviet Union are generally thought to be well known, they can be erroneous by up to tens of kilometers. Information (maps, photographs, descriptions) published in radionuclide contamination and environmental studies, combined with satellite imagery, allow for the improvement of the coordinates of these detonations. We are able to link disturbed areas visible in satellite imagery to probable detonation sites for all PNEs conducted in the Sakha Republic (Yakutia), Russia, and improve on, or confirm, previously published solutions; taking possible uncertainties and alternative sites into consideration, all of them can be located to GT0 or GT1. The improvements are most pronounced for Crystal, where a mound over the detonation site can be identified, and for detonations conducted for the purpose of enhanced petroleum recovery near Tas‐Yuryakh.

Seismotectonic studies of the pleistoseist area of the Ms = 6.9 Ilin-Tass earthquake in northeast Yakutia

The complex seismotectonic studies of the pleistoseist area of the Ilin-Tas earthquake (Ms = 6.9), one of the strongest seismic events ever recorded by the regional seismic network in northeastern Russia, are carried out. The structural tectonic position, morphotectonic features of present-day topography, active faults, and types of Cenozoic deformations of the epicentral zone are analyzed. The data of the instrumental observations are summarized, and the manifestations of the strong seismic events in the Yana–Indigirka segment of the Cherskii seismotectonic zone are considered. The explanation is suggested for the dynamical tectonic setting responsible for the Andrei-Tas seismic maximum. This setting is created by the influence of the Kolyma–Omolon indenter, which intrudes into the Cherskii seismotectonic zone from the region of the North American lithospheric plate and forms the main seismogenic structures of the Yana–Indigirka segment in the frontal zone (the Ilin-Tas anticlinorium). The highest seismic potential is noted in the Andrei- Tas block—the focus of the main tectonic impacts from the Kolyma–Omolon superterrane. The general trend of this block coincides with the orientation of the major axis of isoseismal ellipses (azimuth 50°–85°), which were determined from the observations of macroseismic effects on the ground after the Uyandina (Ms = 5.6), Andrei-Tas (Ms = 6.1), and Ilin-Tas (Ms = 6.9) earthquakes.

Formation dynamics of fault-block structures in the eastern segment of the Baikal-Stanovoi seismic belt

The combined analysis of geological-geophysical characteristics of active faults, morphotectonic features of the relief, and data of satellite measurements and on seismicity in the southeastern Aldan-Stanovoi block (the eastern flank of the Olekma-Stanovoi seismotectonic zone) made it possible to reconstruct the kinematic development of recent falt-block structures with the defining conjugate systems of main seismogenerating faults located in the zone of dynamic influence of three major lithospheric plates: Eurasian, Amur, and Sea of Okhotsk.

Correction to “Current deformation rates and extrusion of the northwestern Okhotsk plate, northeast Russia”

[1] Northeast Asia is a region of broad deformation resulting from the convergence of the Eurasian (EU) and North American (NA) plates. Part of this convergence has been suggested to be relieved by the extrusion and deformation of the Okhotsk plate (OK). Three models for the deformation of the seismically active northwestern corner of the Okhotsk plate, based on different modes of deformation partitioning, are calculated and compared to observations from GPS, seismicity, and geology. The results suggest that this region is being extruded southeastward and deforming internally by a mixture of pure contraction, ‘‘smooth’’ extrusion, and ‘‘rigid’’ extrusion. Calculated extrusion rates are 3–5.5 mm/yr, comparable to estimates from geologic data, and internal deformation rates are 3.0 10 9 yr . Internal deformation may be only partially accommodated by seismicity, but the short time span of seismic data leaves this subject to large uncertainty. Citation: Hindle, D., K. Fujita, and K. Mackey (2006), Current deformation rates and extrusion of the northwestern Okhotsk plate, northeast Russia, Geophys. Res. Lett., 33, L02306, doi:10.1029/2005GL024814.