A study of heat transport at the ice base and structure of the under-ice water layer in Southern Baikal

Experimental data and a new model of ice buildup are used to assess and to study variations of heat flux at the water–ice interface. The latter plays an important part in ice cover formation but still is poorly known because of the lack of field temperature measurements with sufficient spatial and temporal resolution along the phase transition boundary, which knowledge gap is filled by this study.     

Chaos and Wavefront Reversal for Long-Range Sound Propagation

Doklady Earth Sciences - Long-range sound propagation in the deep ocean is considered. Attention is concentrated on the procedure of acoustic wavefield refocusing by means of the wavefront...     

Massive identification of asteroids in three-body resonances

An essential role in the asteroidal dynamics is played by the mean motion resonances. Two-body planet–asteroid resonances are widely known, due to the Kirkwood gaps. Besides, so-called three-body mean motion resonances exist, in which an asteroid and two planets participate. Identification of asteroids in three-body (namely, Jupiter–Saturn–asteroid) resonances was initially accomplished by Nesvorný and Morbidelli (Nesvorný D., Morbidelli, A. [1998]. Astron. J. 116, 3029–3037), who, by means of visual analysis of the time behaviour of resonant arguments, found 255 asteroids to reside in such resonances. We develop specialized algorithms and software for massive automatic identification of asteroids in the three-body, as well as two-body, resonances of arbitrary order, by means of automatic analysis of the time behaviour of resonant arguments. In the computation of orbits, all essential perturbations are taken into account. We integrate the asteroidal orbits on the time interval of 100,000 yr and identify main-belt asteroids in the three-body Jupiter–Saturn–asteroid resonances up to the 6th order inclusive, and in the two-body Jupiter–asteroid resonances up to the 9th order inclusive, in the set of ～250,000 objects from the “Asteroids – Dynamic Site” (AstDyS) database. The percentages of resonant objects, including extrapolations for higher-order resonances, are determined. In particular, the observed fraction of pure-resonant asteroids (those exhibiting resonant libration on the whole interval of integration) in the three-body resonances up to the 6th order inclusive is ≈0.9% of the whole set; and, using a higher-order extrapolation, the actual total fraction of pure-resonant asteroids in the three-body resonances of all orders is estimated as ≈1.1% of the whole set.     

Community Structure in the Amber Forest: Study of the Arthropod Syninclusia in the Rovno Amber(Late Eocene of Ukraine)

<正>Arthropodan syninclusions in the Late Eocene Rovno amber were examined using x~2 to reveal correlation of the component groups(some taxa of Diptera,ants,aphids,and mites) supposedly indicative of the biocoenotic relationships in the ancient amber forest.Three tightly correlated groups were identified,representing a putative aerial plankton guild(Chironomidae+Ceratopogonidae) and two tree-trunk guilds,one of which (Dolichopodidae+Germaraphis) is possibly connected to more open or/and more hygrophilous habitats than the other(Sciara zone Diptera +Acarusrhombeus).The ants were not linked with any of the above components.     

Pseudo-outcrop Visualization of Borehole Images and Core Scans

A pseudo-outcrop visualization is demonstrated for borehole and full-diameter rock core images to augment the ubiquitous unwrapped cylinder view and thereby assist nonspecialist interpreters. The pseudo-outcrop visualization is equivalent to a nonlinear projection of the image from borehole to earth frame of reference that creates a solid volume sliced longitudinally to reveal two or more faces in which the orientations of geological features indicate what is observed in the subsurface. A proxy for grain size is used to modulate the external dimensions of the plot to mimic profiles seen in real outcrops. The volume is created from a mixture of geological boundary elements and texture, the latter being the residue after the sum of boundary elements is subtracted from the original data. In the case of measurements from wireline microresistivity tools, whose circumferential coverage is substantially <100 %, the missing circumferential data are first inpainted using multiscale directional transforms, which decompose the image into its elemental building structures, before reconstructing the full image. The pseudo-outcrop view enables direct observation of the angular relationships between features and aids visual comparison between borehole and core images, especially for the interested nonspecialist.     

Tritium in the snow cover at mid-taiga landscapes in central Yakutia

The paper presents data on the distribution of tritium, a hydrogen radioactive isotope, in the snow cover of mid-taiga landscapes in central Yakutia. Regional tritium escape to the atmosphere in the late 20th century and its accumulation in the snow cover resulted from regional atmospheric transfer and corresponded to the concentration of this isotope in the snow cover at the South Pole. Tritium concentration in the snow cover had almost tripled by 2013. Tritium concentration in the snow cover is correlated with the human population of the settlement zone. The long-term anthropogenic contamination in the area is caused first of all by atmospheric fallouts of radioactive products of the 2011 Fukushima accident.     

Shallow velocity–depth model imaging by refraction tomography1

A tomographic imaging technique combined with coherence inversion is proposed for constructing a near-surface model from refraction events. A model obtained from coherence inversion serves as a good background model for the tomographic reconstruction. A simultaneous iterative reconstruction technique (SIRT) algorithm was used for this purpose. This is a simple algorithm and can be easily adapted to irregular acquisition geometry and limited angular aperture. Using synthetic data it was shown that the proposed procedure can be used for determination of local velocity anomalies in a shallow subsurface. The technique was also tested on a real data set.     

Sea Level Fluctuations as a Key Factor in Delta Formation

Water Resources - Based on studies of the geological and geomorphological structure of the mouth areas of the Ob, Pyasina, Khatanga, and Lena rivers, a model for delta development as a result of...     

Multifocusing revisited ‐ inhomogeneous media and curved interfaces*

We review the multifocusing method for traveltime moveout approximation of multicoverage seismic data. Multifocusing constructs the moveout based on two notional spherical waves at each source and receiver point, respectively. These two waves are mutually related by a focusing quantity. We clarify the role of this focusing quantity and emphasize that it is a function of the source and receiver location, rather than a fixed parameter for a given multicoverage gather. The focusing function can be designed to make the traveltime moveout exact in certain generic cases that have practical importance in seismic processing and interpretation. The case of a plane dipping reflector (planar multifocusing) has been the subject of all publications so far. We show that the focusing function can be generalized to other surfaces, most importantly to the spherical reflector (spherical multifocusing). At the same time, the generalization implies a simplification of the multifocusing method. The exact traveltime moveout on spherical surfaces is a very versatile and robust formula, which is valid for a wide range of offsets and locations of source and receiver, even on rugged topography. In two‐dimensional surveys, it depends on the same three parameters that are commonly used in planar multifocusing and the common‐reflection surface (CRS) stack method: the radii of curvature of the normal and normal‐incidence‐point waves and the emergence angle. In three dimensions the exact traveltime moveout on spherical surfaces depends on only one additional parameter, the inclination of the plane containing the source, receiver and reflection point. Comparison of the planar and spherical multifocusing with the CRS moveout expression for a range of reflectors with increasing curvature shows that the planar multifocusing can be remarkably accurate but the CRS becomes increasingly inaccurate. This can be attributed to the fact that the CRS formula is based on a Taylor expansion, whereas the multifocusing formulae are double‐square root formulae. As a result, planar and spherical multifocusing are better suited to model the moveout of diffracted waves.