Nonequilibrium carbon ionization states and the extragalactic far-UV background with HeII absorption

Using nonequilibrium calculations of the ionic states and the recently calculated extragalactic ultraviolet background radiation with absorption by intergalactic HeII we determine the ratios of CIII to CIV expected at z∼2–3, as functions of metallicity, gas density and temperature. We constrain the spectrum of the extragalactic ultraviolet background radiation by fitting the observed abundance ratios carbon ions at these redshifts with those expected from different models of the background radiation. Our analysis of the observed ratios shows that ‘delayed reionization’ models, which assume a large fraction of HeII at z∼3, is not favored by data. Our results suggest that HeII reionization was inhomogeneous, consistent with the predictions from recent simulations.     

Estimation of the buoyancy profile on the dispersion characteristics of internal waves

In this paper an interaction method is proposed for estimating the buoyancy frequency as a function of depth based on the frequency dependence of wave numbers of internal normal waves. Examples are given of the numerical reconstruction of buoyancy frequency profiles demonstrating convergence of the algorithm. An iterative scheme for the solution of the given problem with an expanded convergence area is obtained on the basis of iteration by stages.Translated by M M. Trufanov.     

Geometry of the fault zone of the 2003 Ms = 7.5 Chuya earthquake and associated stress fields, Gorny Altai

The co-seismic deformations produced during the September 27, 2003 Chuya earthquake (Ms = 7.5) that affected the Gorny Altai, Russia, are described and discussed along a 30 km long segment. The co-seismic deformations have manifested themselves both in unconsolidated sediments as R- and R′-shears, extension fractures and contraction structures, and in bedrock as the reactivation of preexisting schistosity zones and individual fractures, as well as development of new ruptures and coarse crushing zones. It has been established that the pattern of earthquake ruptures represents a typical fault zone trending NW–SE with a width reaching 4–5 km and a dextral strike–slip kinematics. The initial stress field that produced the whole structural pattern of co-seismic deformations during the Chuya earthquake, is associated with a transcurrent regime with a NNW–SSE, almost N–S, trending of compressional stress axis (σ₁), and a ENE–WSW, almost E–W, trending of tensional stress axis (σ₃). The state of stress in the newly-formed fault zone is relatively uniform. The local stress variations are expressed in insignificant deviation of σ₁ from N–S to NW–SE or NE–SW, in short-term fluctuations of relative stress values in keeping their spatial orientations, or in a local increase of the plunge angle of the σ₁. The geometry of the fault zone associated with the Chuya earthquake has been compared with the mechanical model of fracturing in large continental fault zones with dextral strike–slip kinematics. It is apparent that the observed fracture pattern corresponds to the late disjunctive stage of faulting when the master fault is not fully developed but its segments are already clearly defined. It has been shown that fracturing in widely different rocks follows the common laws of the deformation of solid bodies, even close to the Earth surface, and with high rates of movements.     

水文地质学的新概念及其生态问题

水文地质学最初是由地质学及水文学相结合而形成的一门学科，它基本上采用地质学的研究方法。从本世纪７０年代中期开始，研究地下水的水文地质学已逐渐变为研究地下水圈的学科。地下水圈是指地壳内部的统一的含水系统，它包含有相互作用的不同状态和形式的Ｈ２Ｏ。近年来，一些新理论的引入，拓宽了原有水文地质学的概念，使之从对现象的研究转向为对过程及其规律的研究。水文地质学传统的和新的问题应在适当的工程标准上予以解决，同时应重视其生态效应。水是地球内部具有高度流动性的物质，因此，人类活动对岩石圈的影响将首先导致水文地质条件的变化，并进而引起地下水圈的污染、水的枯竭及自然条件的恶化。文章主要论述生态水文地质学研究的目的、原则及生态水文地质系统的体系。生态水文地质学研究的目的是提出管理地下水圈体系及其质量状态的方法。     

Equilibria in the gravitational field of a triangular body

The existence, stability and bifurcation analysis is performed for equilibria of a material point in the gravitational field of three homogeneous penetrable balls fixed in absolute frame. The radii of the balls are assumed finite. In the case when the mass distribution admits a symmetry axis, analytic expressions are written out, allowing one to investigate the properties of equilibrium positions located both on the symmetry axis and outside it. The stability of solutions is studied; domains with different instability degree are described.     

Rheology and strength of the lithosphere

Mechanical properties of lithosphere are of primary importance for interpretation of deformation at all spatial and time scales, from local scale to large-scale geodynamics and from seismic time scale to billions of years. Depending on loading conditions and time scale, lithosphere exhibits elastic, brittle (plastic) or viscous (ductile) properties. As can be inferred from rock mechanics data, a large part of the long-term lithospheric strength is supported in the ductile or ductile-elastic regime, while it also maintains important brittle strength. Yet, at short seismic time scale (s), the entire lithosphere responds in elastic/brittle-elastic regime. Even though rock mechanics experiments provide important insights into the rheological properties of the lithosphere, their conditions (e.g., time scales, strain rates, temperature and loading conditions) are too far from those of real Earth. Therefore, these data cannot be reliably extended to geological time- and spatial scales (strain rates ∼10⁻¹⁷ to 10⁻¹³ s⁻¹) without additional parameterization or validation based on geological time scale observations of large-scale deformation. For the oceanic lithosphere, the Goetze and Evan’s brittle-elastic-ductile yield strength envelopes (YSEs) were validated by geodynamic scale observations such as the observations of plate flexure. However, oceanic lithosphere behavior in subduction zones and passive continental margins is strongly conditioned by the properties of the continental counterpart, whose rheology is less well understood. For continents and continental margins, the uncertainties of available data sources are greater due to the complex structure and history of continental plates. For example, in a common continental rheology model, dubbed “jelly sandwich”, the strength mainly resides in crust and mantle, while in some alternative models the mantle is weak and the strength is limited to the upper crust. We address the problems related to lithosphere rheology and mechanics by first reviewing the rock mechanics data, T_e (flexure) and T_s (earthquake) data and long-term observations such as folding and subsidence data, and then by examining the physical plausibility of various rheological models. For the latter, we review the results of thermo-mechanical numerical experiments aimed at testing the possible tectonic implications of different rheology models. In particular, it appears that irrespective of the actual crustal strength, the models implying weak mantle are unable to explain either the persistence of mountain ranges for long periods of time or the integrity of the subducting slabs. Although there is certainly no single rheology model for continents, the “jelly sandwich” is a useful first-order model with which to parameterize the long-term strength of the lithosphere. It is concluded that dry olivine rheology laws seem to represent well the long-term behavior of mantle lithosphere in oceans, margins and continents. As to the continent and margin crust rheology, analysis of the results of thermo-mechanical models and of T_e data based on the most robust variants of flexural models, suggests that continental plates with T_e 30-50% smaller than their theoretical mechanical thickness h_m (i.e. T_e = 20-60 km) should be characterized by a weak lower or intermediate crustal rheology enabling mechanical decoupling between crust and mantle. Older plates such as cratons are strong due to crust-mantle coupling and specific properties of the cratonic mantle lithosphere.