Confirmation of an early estimation for an increase in the seismic activity towards the end of the twentieth century

A new series analysis from 1970 to 2015 of earthquakes with moment magnitude Mw?≥?6.5 on a global scale, confirms an early estimation, since the 1980s that seismic activity after 1990 would be increased in relation to the previous period.     

Estimating the energy of an ice-covered flow

Energy balance of an ice-covered flow in a constant-slope reach of a regulated river is considered. The ratio of energy losses for viscous friction to the total flow energy is evaluated. The turbulence intensities of an open and ice-covered flows are compared.Translated from Vodnye Resursy, Vol. 32, No. 1, 2005, pp. 48–54.Original Russian Text Copyright © 2005 by Dolgopolova.     

Propagation of Electromagnetic Field Pulse in an Inhomogeneous Medium Based on the Results of an Analytical Continuation of the Field

The possibility of visually controlling the propagation of an electromagnetic pulse in an inhomogeneous medium based on an analytical continuation of the observed field is presented.     

On the fast movements of the thermosphere: an interpretation

We examine the oscillations of the meridional neutral wind in the F region as seen by the EISCAT radar. We propose an interpretation in term of eddies (tourbillons) of typical size of a few tens to a few hundreds of kilometers. The observed rotation velocity is a few hundreds of meters per second. We suggest that the tourbillons are a common feature of thermospheric movements. We propose an optical experiment to check the validity of this assumption.     

Uranium as an indicator of the origin of the Tethyan ophiolites

The distribution of uranium in minerals and rocks of the ophiolitic sequences from the Northern Apennines (Italy) and the Hellenides (Greece) of the Tethyan mountain belt has been investigated by fission-track mapping. Whole-rock U abundances, ranging from 11 to 74 ppb in ultramafic rocks, from 13 to 54 ppb in gabbroic rocks, from 73 to 281 ppb in basalts and from 279 to 900 ppb in spilites, partially reflect the post-crystallization history of the rocks. Among the fresh relics of primary rock-forming minerals, clinopyroxene has the highest U content. The estimated original U concentration of ultramafic rocks is about 1 – 10 ppb. These rocks do not appear to represent the primary undepleted mantle material. U distribution in the analyzed suites of ophiolites is consistent with a model for alpine-type ophiolites, where harzburgites and lherzolites of the basal ultramafic zone represent the residuum after extraction of oceanic tholeiitic magma. The segregated basaltic liquid either extruded rapidly as basalts or underwent magmatic differentiation in a quiet environment producing mineral accumulates as troctolites and gabbros.     

Analysis of the hydrological behaviour of an urbanizing basin

Suburban areas undergo rapid land‐use changes due to urban growth. Consequently, the mitigation of hydrological impacts is a major issue in the field of flood and water pollution management. Nevertheless, suburban catchments have seldom been studied. This paper presents a method for analyzing the hydrological behaviour of suburban catchments; the particular method is tested on the Chézine catchment, located in a suburban area of Nantes (western France). Chézine provides a typical example of a suburban catchment, yet features the unique behaviour of a response time ranging from 1 to 6 h. It is proposed herein to classify rainfall‐runoff events in homogeneous groups according to their flow coefficient. A group of events is characterized by its mean flow coefficient and by its transfer function, which are considered as the signatures of the hydrological behaviour of these similar events. The transfer function is identified from the available series of rainfall and outflow data. The identified transfer functions serve to estimate the localization of contributing zones over the basin by estimating the basin transfer function from flowpaths. The consistency of these assumptions is then verified by comparing the estimated transfer function with the identified one. The application of this method to the Chézine catchment demonstrates that it is possible to distinguish various types of hydrological behaviour regimes associated with significantly different transfer functions. The joint analysis of the flow coefficient and transfer function of each group confirms that the Chézine catchment reacts like an urban basin with just the urban zones contributing to runoff under dry conditions. Otherwise, the wetter the initial state, the greater the tendency of this basin to react like a natural basin, as reflected by the different transfer function shapes. These results confirm the validity of the proposed method to analyse the various behaviour regimes of suburban catchments. In addition, this method helps define the specifications of hydrological models suited to suburban catchments. Copyright © 2013 John Wiley & Sons, Ltd.     

Retrieval of source parameters of an event of the 2000 West Bohemia earthquake swarm assuming an anisotropic crust

We propose an inversion scheme for retrieval of characteristics of seismic point sources, which in contrast to common practice, takes into account anisotropy. If anisotropy is neglected during inversion, the moment tensors retrieved from seismic waves generated by sources situated in anisotropic media may be biased. Instead of the moment tensor, the geometry of the source is retrieved directly in our inversion; if necessary, the moment tensor can be then determined from the source geometry aposteriori. The source geometry is defined by the orientation of the slip vector and the fault normal as well as the strength of the event given by the size of the slip and the area of the fault. This approach allows direct interpretation of the source geometry in terms of shear and tensile faulting. It also makes possible to identify volumetric source changes that occur during rupturing. We apply the described algorithm to one event of the 2000 West Bohemia earthquake swarm episode. For inversion we use information of the direct P waves. The structure is approximated by three different models determined from travel-time observations. The models are inhomogeneous isotropic, inhomogeneous anisotropic, and homogeneous anisotropic. For these models we obtain seismic moments M_T = 3.2 − 3.8 × 10¹⁴ Nm and left-lateral near-vertical oblique normal faulting on a N-S trending rupture surface. The orientation of the rupture surface is consistent with fault-plane solutions of earlier studies and with the spatial distribution of other events during this swarm. The studied event seems to be accompanied by a small amount of crack opening. The amount of crack opening is slightly reduced when the inhomogeneous anisotropic model is assumed, but it persists. These results and additional independent observations seem to indicate that tensile faulting occurs as a result of high fluid pressure.     

Modeling the distribution of Populus euphratica in the Heihe River Basin,an inland river basin in an arid region of China

Populus euphratica is a dominant tree species in riparian Tugai forests and forms a natural barrier that maintains the stability of local oases in arid inland river basins. Despite being critical information for local environmental protection and recovery, establishing the specific spatial distribution of P. euphratica has rarely been attempted via precise and reliable species distribution models in such areas. In this research, the potential geographic distribution of P. euphratica in the Heihe River Basin was simulated with MaxEnt software based on species occurrence data and 29 environmental variables. The result showed that in the Heihe River Basin, 820 km~2 of land primarily distributed along the banks of the lower reaches of the river is a suitable habitat for P. euphratica. We built other MaxEnt models based on different environmental variables and another eight models employing different mathematical algorithms based on the same 29 environmental variables to demonstrate the superiority of this method.MaxEnt based on 29 environmental variables performed the best among these models, as it precisely described the essential characteristics of the distribution of P. euphratica forest land. This study verified that MaxEnt can serve as an effective tool for species distribution in extremely arid regions with sufficient and reliable environmental variables. The results suggest that there may be a larger area of P. euphratica forest distribution in the study area and that ecological conservation and management of P.euphratica should prioritize suitable habitat. This research provides valuable insights for the conservation and management of degraded P. euphratica riparian forests.     

Transport of the environmental radionuclides in an alpine watershed

The radionuclides¹³⁷Cs,²¹⁰Pb and⁷Be have been examined in the alpine Rhoˆne watershed (Switzerland) during a period of two years in order to evaluate their usefulness as tracers of the removal and transport rate of top-soil particles and particle-reactive contaminants of atmospheric origin. The specific activities of the radionuclides in fluvial suspension show a distinct seasonal pattern which depends on the hydrologic regime of the stream and the sources of the suspended matter. Input-output budgets based on the atmospheric deposition and fluvial removal of three radionuclides in the alpine Rhoˆne watershed are used to estimate their erosional residence times. The simplest one box model yields mean residence times of about 800 and 1400 years for¹³⁷Cs and²¹⁰Pb, respectively. The removal rate of short-lived⁷Be suggests that a part of the watershed (0.6–2.3% of the total surface) is exposed to a rapid erosion, in which the mean residence time of the radionuclides is in the range of 1–220 days. This has little influence on the calculated residence time of¹³⁷Cs but increases the estimated residence time of²¹⁰Pb in soil to over 1800 years. The use of²¹⁰Pb-⁷Be pair in fluvial output may be very helpful in the assessment of the impact of atmospheric pollutants on the water quality in rivers and lakes.     

Small Rivers and the Ecological State of an Area

Data from surveying small rivers in Moscow and Tver oblasts are used to assess the anthropogenic load on their watersheds. Expert estimates of the effect of such load onto the state of surface water are made. Integral characteristics and similarity criteria of the hydroecological conditions of small rivers are substantiated.     

On the dynamic response of an infinite Bernoulli-Euler beam

Summary This paper presents a theory of the transient Bernoulli-Euler beam problem on an elastic foundation which takes into account the effects of axial load and linear damping. An analytical solution of the steady state and the transient components has been obtained due to physically realistic load distributions. With a view to extend its practical applicability, the characteristic features of the solution are explored. Several limiting situations are investigated as special cases. It is shown that the steady state vibration can be achieved as the limit of the solution of the transient problem.     

Effects of an oil spill in the northern Baltic

Oil pollution from the tanker Palva which ran aground in Finnish waters in 1969 provides an example of the hazards of oil spills in cold waters. The Palva incident and its aftermath were studied by Finnish biologists and some of their findings are reported here. The chief casualties were eider ducks, but fortunately long-term effects appear to have been small.     

Sedimentation in the riparian zone of an incising river

This paper focuses on one aspect of riparian zone change associated with channel incision. It presents information on sedimentation within the riparian zone of the River Garonne, France, derived from both historical and contemporary sources. The riparian zone investigated is morphologically complex, containing a remnant island and cut‐off channel. Information drawn from historical and contemporary sources permits the reconstruction of channel planform and cross‐profile change, as well as an assessment of changes in riparian zone sedimentation rates and patterns. Very significant changes are identified over the last 50 years: a change from a multiple thread to single thread channel planform; high rates of riparian zone sedimentation of the order of 0·5 to 2·5 cm a⁻¹; clear spatial patterns in over‐bank sedimentation, reflecting topographic and vegetational variations and flood event magnitude; and a reduction in morphological and vegetational diversity through the period, which is expected to continue as the zone is transformed into an increasingly homogeneous sediment sink. Copyright © 2001 John Wiley & Sons, Ltd.     

Magnetospheric-ionospheric convection in an open model of the magnetosphere

Magnetospheric-ionospheric convection has been calculated for an open model of the magnetosphere with an ellipsoidal magnetopause in an approximation of uniform IMF. It is assumed that only 0.1 part of IMF falls in the magnetosphere as a result of the effect of IMF shielding by the magnetopause. The modeling of convection has been performed for the cases when the IMF B _z component is directed southward and the B _y component is westward or eastward. A Tsyganenko 96 model has been used as a magnetospheric model. The model calculations are compared with the data on the ion drift in the ionosphere. A certain disagreement between the experimental and calculated data has been found in the pattern of convection on the dayside of the ionosphere for the case of B _y >0, which manifested itself in the dimensions of a convection “tongue” and in the position of the convection throat on the dayside. It has been indicated that the convection pattern agrees with the results of observations if the azimuthally inhomogeneous magnetospheric conductivity is taken into account.     

Modeling the thermal evolution of an active geothermal system

Temperature inversions at shallow to moderate depths have been observed commonly in boreholes drilled in geothermal areas. The inversions result from thermal disequilibria generated by steam and/or hydrothermal fluids invading shallow horizontal, or sub-horizontal fractures, or permeable horizons, from a deep vertical, or sub-vertical feeder-fracture.Subsurface distribution of temperatures in Momotombo geothermal area of Nicaragua, Central America, indicates that the anomaly is generated by steam and water, convecting in a narrow feeder-fracture-zone located at the western edge of the field. The north-trending zone of the feeder-fracture is bound on the west by the area of massive, impermeable andesitic rocks, and is capped by an impermeable, approximately 300 m. thick silica-cap, which seals if from the ground surface. The thermal fluids penetrate a system of horizontal, or sub-horizontal fractures, extending east of the feeder-fracture beneath the silica cap. The flow of thermal fluids eastward through the system of the horizontal, or sub-horizontal fractures is generating a plume-like geothermal anomaly, which is expressed by the temperature inversion zone pervasive in the boreholes to the east of the feeder-fracture.A time-dependant model for a semi-infinite half-space (z > 0) in contact with a hot, well stirred, isotropic fluid flowing through an aquifer overlain by a finite space of constant thickness is solved for the data collected from the Momotombo geothermal boreholes. Curve fitting between the simulated and observed temperature/depth profiles suggests that the thermo-tectonic events which caused the present-day Momotombo hydrothermal system occurred approximately 5,500 years ago, following development of vertical, or subvertical fractures along a N5°E trending faultline. Hot fluids emerging from these fractures move eastward through a system of horizontal, or sub-horizontal fractures, with a velocity of 11 to 20 m/yr.     

Polarization of the magneto-telluric fields over an anisotropic earth

Summary The effect of an anisotropic earth on an elliptically polarized incident magnetic field is investigated. A new method is developed for delineating the local conductivity structure using the polarization parameters of the magneto-telluric fields.