Internal deformation of Sikhote Alin volcanic belt, far eastern Russia: Paleocene paleomagnetic results

We present paleomagnetic results of Paleocene welded tuffs of the 53–50 Ma Bogopol Group from the northern region (46°N, 137°E) of the Sikhote Alin volcanic belt. Characteristic paleomagnetic directions with high unblocking temperature components above 560 °C were isolated from all the sites. A tilt-corrected mean paleomagnetic direction from the northern region is D=345.8°, I=49.9°, α₉₅=14.6° (N=9). The reliability of the magnetization is ascertained through the presence of normal and reversed polarities. The mean paleomagnetic direction from the northern region of the Sikhote Alin volcanic belt reflects a counterclockwise rotation of 29° from the Paleocene mean paleomagnetic direction expected from its southern region. The counterclockwise rotation of 25° is suggested from the paleomagnetic data of the Kisin Group that underlies the Bogopol Group. These results establish that internal tectonic deformation occurred within the Sikhote Alin volcanic belt over the past 50 Ma. The northern region from 44.6° to 46.0°N in the Sikhote Alin volcanic belt was subjected to counterclockwise rotational motion through 29±17° with respect to the southern region. The tectonic rotation of the northern region is ascribable to relative motion between the Zhuravlevka terrane and the Olginsk–Taukhinsk terranes that compose the basements of the Sikhote Alin volcanic belt.     

Structure,Matter Composition,and Deep Structure of the Oceanic Slope of the Central Kuril Islands: New Evidence

The results of reinterpretation of the geophysical data obtained during the study of the central sector of the Kuril Island Arc (2005–2010) are reported. The new boundaries of the shallow bedding of the basement and its block uplifts of varied composition are defined within the previously discovered zone of tectonic stretching and destruction of the Vityaz submarine ridge and interarc trough. Interblock depressions filled with sedimentary and volcanogenic-sedimentary rocks are distinguished. Areas represented by volcanoplutonic complexes including basic and sialic series (up to granite) are distinguished within the unbroken basement of the Vityaz Ridge. Intrusions and volcanic edifices composed of basic rocks are registered on the whole area studied. The relationship between the formation of the destruction zone and the geodynamic processes in the mantle is illustrated by the map of the Moho relief and structural-density model of the Earth’s crust.     

Peculiarities of the fluid regime in the lithosphere of the junction zone between South Primorye and the Sea of Japan from the comprehensive geophysical data

New data on the fluid lithospheric regime in the junction zone of the continent and the marginal seas are presented. For the first time, this problem was solved by the comprehensive interpretation of the geophysical methods, including magnetotelluric and geomagnetic-variation sounding, unique investigations of the variations of the electric field along the Japan Sea Cable (JASC), structural-density modeling, thermometry, and thermodynamics. A joint analysis of the distribution of the electric conductivity, density, and temperature in the lithosphere made it possible to substantiate the participation of mantle fluids in the formation of lithotectonic complexes that are quite different beneath the continent and the marginal Sea of Japan.     

Gravity and Displacement Variations in the Areas of Strong Earthquakes in the East of Russia

The modern gravimetry methods are capable of measuring gravity with an accuracy of up to 10^–10 of the normal value, which is commensurate with the accuracy of the up-to-date methods of displacement measurements by satellite geodesy. Significant changes, e.g., in the coseismic displacements of the Earth’s surface are recorded in the zones of large earthquakes. These changes should manifest themselves in the variations of gravity. Absolute measurements have been conducted by various modifications of absolute ballistic gravimeters GABL since the mid-1970s at the Klyuchi point (Novosibirsk) in the south of the West Siberian plate. Monitoring observations have been taking place in the seismically active regions since the 1990s. In this paper we consider the results of the long-term measurements of the variations in gravity and recent crustal displacements for different types of earthquakes (the zones of shear, extension, and compression). In the seismically active areas in the east of Russia, the longest annual series of absolute measurements starting from 1992 was recorded in the southeastern segment of Baikal region. In this area, the Kultuk earthquake with magnitude 6.5 occurred on August 27, 2008, at a distance of 25 km from the observation point of the Talaya seismic station. The measurements in Gornyi (Mountainous) Altai have been conducted since 2000. A strikeslip earthquake with magnitude 7.5 took place in the southern segment of the region on September 27, 2003. The effects of the catastrophic M = 9.0 Tohoku, Japan, earthquake of March 11, 2011 were identified in Primor’e in the far zone of the event. The empirical data are consistent with the results of modeling based on the seismological data. The coseismic variations in gravity are caused by the combined effect of the changes in the elevation of the observation point and crustal deformation.     

Structural and geological characteristics of a “seismic gap” in the central part of the Kuril Island Arc

The results of the cruise of R/V Akademik M.A. Lavrentiev conducted by the Pacific Institute of Oceanology, Far East Division of the Russian Academy of Sciences and the Shirshov Institute of Oceanology, Russian Academy of Sciences in August to September 2005 are considered. The aim of the works was to specify the tectonic structure, seismogenic potential, and tsunamigenic hazard of the central segment of the Kuril Island Arc. The complex studies involved single-channel seismic profiling, gravimetry, magnetometry, detailed bathymetry, dredge sampling of sea-floor rocks and sediments, and gas geochemistry. Geophysical and geological data are reported. It was demonstrated that the target area is an active tectonic destruction zone, the zone boundaries were outlined, and the main internal structural and compositional heterogeneities were identified.     

Thicknesses and types of the crust beneath the Sea of Japan inferred from marine and satellite gravimetric investigations

The combined gravimetric, altimetric, and seismic data used for calculating the crust thickness beneath the Sea of Japan revealed its different types in this region: oceanic and continental with different degrees of destruction. It is shown that the crust thickness derived from satellite altimetry is well consistent with that calculated from the data obtained by on-board gravimetric observations.     

Gravitational stability of dark energy in galaxies and clusters of galaxies

We analyze the behavior of the scalar field as dark energy of the Universe in a static world of galaxies and clusters of galaxies. We find the analytical solutions of evolution equations of the density and velocity perturbations of dark matter and dark energy, which interact only gravitationally, along with the perturbations of metric in a static world with background Minkowski metric. It was shown that quintessential and phantom dark energy in the static world of galaxies and clusters of galaxies is gravitationally stable and can only oscillate by the influence of self-gravity. In the gravitational field of dark matter perturbations, it is able to condense monotonically, but the amplitude of density and velocity perturbations on all scales remains small. It was also illustrated that the “accretion” of phantom dark energy in the region of dark matter overdensities causes formation of dark energy underdensities-the regions with negative amplitude of density perturbations of dark energy.     

Evolution of a spherically symmetric dust-like cloud in ΛCDM models

We investigate the evolution of a spherically symmetric dust-like cloud at the linear and nonlinear stages in the framework of ΛCDM models of the universe with nonzero three-space curvature. The evolution conditions are expressed for any redshift z ≥ 0 in terms of the amplitude δ_min of the fluctuation which stops to expand at infinite time, the amplitude δ _ta of the fluctuation which stops to expand at a given moment, and the amplitude δ _c of the fluctuation which collapses at a given moment. These amplitudes are calculated as functions of cosmological model parameters and redshift. The ratios D _nl ^r /D _l of nonlinear amplitude estimates to linear ones and the typical fluctuation scales k _nl /k are approximated by a function of the linear amplitude δ _z .