Nature of the scattered seismic response from zones of random clusters of cavities and fractures in a massive rock

The scattering of elastic energy by random clusters of fractures and/or cavities in a massive rock is studied. The interpretation of the scattered seismic response reveals crucial information about the clusters of inhomogeneities (fractures/cavities), which may correspond to reservoirs. The study is based on a new two‐dimensional numerical‐modelling method that relaxes the constraints on the location and orientation of the inhomogeneities, accounts for inhomogeneities that have almost no volume but a finite surface area (fractures) and improves the accuracy of the calculation when the size of the inhomogeneities is comparable to the mesh size. It is shown that the nature of the seismic response of zones of diffuse fracturing and/or cavities is associated with the non‐uniformity of micro‐inhomogeneities in such zones; accumulations of these micro‐inhomogeneities are known as clusters. The relationship between the non‐uniformity of micro‐inhomogeneities and the strength of the seismic response has been established and measured. Considerable differences in the structure of the seismic response of zones of diffuse fracturing and diffuse cavities have been identified. Converted PS‐waves dominate in the scattered wavefield associated with fractures. This is explained, as the modelling results show, by a greater transparency of fluid‐filled fractures, which reduces the reflected energy of compressional waves. The wavefield associated with cavities is characterized by the predominance (in terms of strength) of compressional PP‐waves. The strength of converted PS‐waves in the scattered wavefields for both media is approximately the same. On the whole, according to the results of the modelling, the energy of the scattered response of fractured reservoirs is considerably less (about two times) than that of cavernous reservoirs.     

A proposed program of observations of extragalactic X-ray sources

It is proposed to carry out an observational test of the hypothesis that active galactic nuclei contain a massive black hole, surrounded by an accretion disk as an energy source. The observational program included 64 objects, selected according the Aldrovandi's model.     

Assessment of Planetary Indices of Geomagnetic Activity Based on Data from Individual Magnetic Observatories in the Russian Sector

Geomagnetism and Aeronomy - The relationships between local indices at stations in the Russian sector and the planetary Ap and Kp indices and the potential to evaluate planetary indices based on...     

Quantitative analysis of clumps in the tidal tails of star clusters

Tidal tails of star clusters are not homogeneous but show well-defined clumps in observations as well as in numerical simulations. Recently, an epicyclic theory for the formation of these clumps was presented. A quantitative analysis was still missing. We present a quantitative derivation of the angular momentum and energy distribution of escaping stars from a star cluster in the tidal field of the Milky Way and derive the connection to the position and width of the clumps. For the numerical realization we use star-by-star N -body simulations. We find a very good agreement of theory and models. We show that the radial offset of the tidal arms scales with the tidal radius, which is a function of cluster mass and the rotation curve at the cluster orbit. The mean radial offset is 2.77 times the tidal radius in the outer disc. Near the Galactic Centre the circumstances are more complicated, but to lowest order the theory still applies. We have also measured the Jacobi energy distribution of bound stars and showed that there is a large fraction of stars (about 35 per cent) above the critical Jacobi energy at all times, which can potentially leave the cluster. This is a hint that the mass loss is dominated by a self-regulating process of increasing Jacobi energy due to the weakening of the potential well of the star cluster, which is induced by the mass loss itself.     

New data on the basement of Franz Josef Land,Arctic region

We have studied pebbles of igneous rocks from the Lower Jurassic sedimentary succession of Hall Island, Franz Josef Land. Pebbles are represented by felsic intrusive and extrusive rocks, often cataclased and greisenized. The U–Pb age of crystallization for zircons of the studied samples yielded the Latest Devonian–Early Carboniferous and Early–Middle Permian ages. In addition, the studied zircons demonstrate a broad scatter of ages, from Middle Paleozoic to Mesozoic, suggesting repeated thermal reworking and metamorphism of granites. It is shown that coeval Late Paleozoic magmatism indicates the similarity of the geological evolution of the northern Barents Sea and the Severnaya Zemlya archipelago.     

Basic-to-acid and acid-to-basic zonation in the sulfur isotope composition of diagenetic sulfide nodules

The typical for marine sediments decrease in the amount of sulfate ion in interstitial solutions with increasing depth owing to sulfate reduction and attenuation of the diffusion of near-bottom waters is manifested as the basic-to-acid zonation in the sulfur isotope composition of the diagenetic pyrite nodules (increase of δ³⁴S values from the center to edge). In sandstones of the Early Carboniferous Emyaksin Formation, which is developed at middle reaches of the Vilyui River (Sakha-Yakutia), we detected a peculiar sulfide nodule. In contrast to common nodules, this nodule is marked by the δ³⁴S value decreasing from 7.5…8.6‰ at the center to –30…–31.4‰ at the edge. Such acid-to-basic zonation is attributed to the origin of nodule in a freshened basin (delta) with a sulfate-depleted environment, which gave way to a sulfate-enriched environment owing to the expulsion brines from the underlying gypsiferous sequences.     

The provenance of terrigenous rocks of the basal horizons of the Uralides of the Baidarata Allochthon (Polar Urals) according to the U–Pb isotope age of detrital zircons

The U–Pb (LA–ICP–MS) age of detrital zircons from the Upper Cambrian–Lower Ordovician terrigenous rocks of the Baidarata Allochthon, which is located in the northern part of the Polar Urals, is determined. The analysis of the youngest zircon population indicates a broad occurrence of the Uralides in this area rather than Pre-Uralides, as was considered previously. The Bedamel island-arc rocks (rather than Timan orogen) were probably the major provenance for the studied sequences. The results of statistical processing of the U–Pb ages of zircons from coeval rocks of Arctic regions suggest similar provenances for the Baidarata Allochthon and Novaya Zemlya and Severnaya Zemlya archipelagoes.     

New data concerning the age and specific features of magmatism of timanides in the southern part of the Lyapin structure (Northern Urals)

New data on composition and age of Precambrian granites and volcanic rocks in the southern part of the Lyapin structure (Northern Urals) are considered. The geochemical features of the igneous rocks are similar to those of the rocks formed in both divergent and convergent environments. In the Late Precambrian (583–553 Ma), the investigated area is assumed to have been a part of the active margin above the mantle plume.