Frontal upwelling in a rotating two-layer fluid

Abstract

This paper describes the source-sink driven flow in a two-layer fluid confined in a rotating annulus. Light fluid is injected at the inner wall, while denser fluid is withdrawn at the outer wall. The interface between the immiscible fluids intersects the bottom and thus produces a front. The net transport from the source to the sink is carried by Ekman layers at the bottom and at the interface, and by Stewartson layers at the side walls. A detached Stewartson layer arises at the front, leading to a pronounced upwelling circulation.     

Observations of subterahertz radiation of solar flares with an RT-7.5 radiotelescope

We analyzed unique observations of two flare events at frequencies of 93 and 140 GHz. The observations were carried out with an RT-7.5 radiotelescope at the Bauman State Technical University (Moscow) using the method of continuous active region tracking with spatial resolutions of 2.5 (at a frequency of 93 GHz) and 1.5 arc-minutes (at 140 GHz). The light curves of the bursts were analyzed and compared with the time profiles of soft and hard X-ray emission obtained by the GOES and RHESSI spacecraft. The radio delete this word flux density spectra were plotted. It was found that the radiation flux at a frequency of 140 GHz exceeded the flux at 93 GHz. This constitutes a new independent confirmation of the presence of a subterahertz flare component, the appearance of which may be associated with the thermal radiation of the hot plasma at the base of flare loops.     

Geothermal constraints on the hydrological regime of the TAG active hydrothermal mound, inferred from long-term monitoring

During August 1994 to March 1995, a period that included ODP Leg 158 drilling, bottom-water and sub-bottom temperatures were continuously logged by a long-term temperature monitoring system ‘Daibutsu’ at the base of the central black-smoker complex (CBC) and within the low heat flow zone at the TAG hydrothermal mound on the Mid-Atlantic Ridge. The temperature of hydrothermal fluid at CBC was also measured with a small high-temperature probe ‘Hobo’. Bottom-water temperature variations measured with Daibutsu at both sites have predominant semi-diurnal periods, causing the sub-bottom temperatures to fluctuate at these periods with reduced amplitudes and phase delays at sub-bottom depths. Seawater entrainment into the mound has been previously suggested at the low heat flow zone. We quantitatively evaluate the seawater entrainment rate at both sites from a one-dimensional numerical model, combined with a heat conduction model for the semi-diurnal variations. The entrainment rate of seawater at the base of CBC is estimated as 1.3±0.5×10⁻⁵ m/s, at least from August 17 to 30, 1994. On the other hand, the seawater entrainment rate at the low heat flow zone was undetected by long-term temperature monitoring at shallow sub-bottom depth. Nevertheless an increase in heat flow observed at the low heat flow zone during ODP drilling can be interpreted as a decrease in the entrainment rate of seawater. Before ODP Leg 158, Daibutsu measured three sub-bottom temperature anomalies at the base of CBC not derived from bottom-water temperature variations and Hobo also detected a CBC fluid temperature anomaly, indicating some natural changes in fluid flow within the mound. Daibutsu and Hobo also measured temperature anomalies during and after drilling at the ODP TAG-1 area. The Hobo temperature anomalies are inferred to have occurred when the cold fluid entrained through the drill holes at TAG-1 site reached or cooled the main fluid path to CBC. The entrained seawater through the drill holes appears to have contributed to dissolution and precipitation of anhydrite within the mound and perhaps affected the local permeability structure inside the mound. The temperature anomalies measured with Daibutsu at the base of CBC may have been induced by the change in the fluid flow pattern as a result of such permeability changes within the mound.     

Investigation of upper mantle structure under young regions of the southeast Pacific using long-period Rayleigh waves

Long-period Rayleigh wave group velocity dispersion curves are presented for paths across the east Pacific Ocean. The records are from the IPG site at Pamatai (Tahiti) and the IDA station at Nana. For the first time, direct-path observations of group velocities up to 300 s have been obtained. This study shows that for young oceanic regions group velocities are low even at long periods. The observations are interpreted in terms of an S-wave velocity model by a generalized inversion scheme. In the models for young ages, the low-velocity zone under the asthenosphere lid is well developed, with a strong velocity gradient at the bottom of this zone, followed at larger depths by a plateau representing a lower-velocity zone, and a marked gradient at 400 km.     

Slow mass movement in the Kangchenjunga area, eastern Nepal Himalaya

Abstract   The rates of the accumulated and continuous displacement of solifluction lobes in the Kangchenjunga area, eastern Nepal Himalaya, were determined using glass fiber tubes and a strain probe. Ground temperature, precipitation and soil moisture were monitored at two sites, whose altitude differed by approximately 100 m, to understand the solifluction process. The average movement rate of the glass fiber tubes on a 31° slope at altitudes of 5412–5414 m a.s.l. was approximately 11 mm/year, being almost threefold greater than that observed on a 22° slope at 5322–5325 ma.s.l. There was no significant difference in the depth of displacement at these sites. The continuous displacement measurement near the ground surface at 5414 m showed permanent downslope movement from early July. Such movement may be attributed to additional moisture supply during the monsoon season. The amplitude of the displacement cycle was highest at the ground surface, and decreased to virtually zero at and below 20 cm in depth. Probable factors leading to the relatively slow rates of downslope displacement at the surface and depth at the studied altitudes are the lack of concurrence of the freeze–thaw cycles and the high moisture condition in the soil, and the low moisture retention capacity of the soil because of steep slopes and superficial desiccation. The rate of displacement may be more pronounced at altitudes above 5600 m because of the freeze–thaw cycles during the summer season.     

博阿断裂西段重复地震识别及断层深部滑移速率研究

本文选取博阿断裂西段周围30 km范围内2010年1月—2015年12月期间9个台站记录到的1272次地震事件的波形记录,利用波形互相关技术从中识别出65组(231次)重复地震,并且基于这些重复地震事件估算该断层的滑移速率.结果显示:该区域重复地震比例为18.2%;博阿断裂阿拉山口—精河段、精河—新源段的平均滑移速率分别约为0.99 mm/a和1.35 mm/a,乌苏—石场段、巴仑台—乌什城段的平均滑移速率分别为1.36 mm/a和2.03 mm/a,这与GPS观测结果基本一致;深部滑移速率的极大值分布在2—10 km深度范围内,其中巴仑台—乌什城段在8 km深度处达到了极大值8.6 mm/a.      

DIKE FORMATION WITH SUBMERGED VANE

1 INTRODUCTION Increasing capital costs, emerging environmental concerns and rising maintenance expenses of conventional river training works around the world have led to the development of submerged vanes in practice. Submerged vanes are being favoured f…     

Laminar hydromagnetic flow in an annulus with uniformly porous walls of different permeability

Summary The problem of steady laminar hydromagnetic flow in a porous annulus of different permeability in the presence of a magnetic field is considered and solved by a method of perturbation. The case when the injection or the withdrawal rate at the outer wall, depending on the sign of the normal velocity at this wall, is greater than or equal to such rate at the inner wall is given in details. Some numerical results regarding the friction coefficients at the walls and the axial pressure coefficient and velocity distribution have been appended.     

Observations on the Bottom Fauna of the Ganga River (between Buxar and Ballia) with Special Reference to Its Role in the Seasonal Abundance of Fresh Water Prawn Macrobrachium birmanicum choprai (Tiwari)

The paper deals with the changes in composition and density of bottom fauna of the Ganga river at Buxar and Ballia in relation to soil texture and water quality observed between March 1984 and Feb. 1986 with its possible role in the seasonal abundance of M. birmanicum choprai. No marked differences were noted in the quality of water at the two centres. The texture of bottom was sandy at both the centres, but the soil at Ballia was found to consist almost of sand with a negligible quantity of clay content. The benthic fauna mainly consisted of dipterans, amphipods and annelids and exhibited a higher abundance at Buxar. It showed a major pulse in the month of March with a minor one in December. The macrobenthos including gastropods and bivalves were abundant during summer (March–June). The bottom fauna on which the prawns generally feed becomes a potential source of food during winter when the prawns get confined to a unit area.     

Analysis of latitudinal distribution of Pi2 geomagnetic pulsations using the generalized variance method

The spatial dynamics of bursts of geomagnetic Pi2-type pulsations during a typical event of a magnetospheric substorm (April 13, 2010) drifting to the pole was investigated using the method of generalized variance characterizing the integral time increment of the total horizontal amplitude of the wave at a given point in the selected time interval. The digital data of Scandinavian profile observations from IMAGE magnetometers with 10-second sampling and data of the INTERMAGNET project observations at the equatorial, middle-latitude and subauroral latitudes with a 1-second sampling were used in the analysis. It was shown that Pi2 pulsation bursts in a frequency band of 8–20 mHz appear simultaneously on a global scale: from the polar to equatorial latitudes with maximum amplitudes at latitudes of the maximum intensity of the auroral electrojet and with a maximum amplitude of geomagnetic pulsations Pi3 within a band of 1.5–6 mHz. The first (left-polarized) intensive Pi2 burst appeared at auroral latitudes several minutes after breakup, while the second (right-polarized) burst occurred 15 min after breakup but at higher (polar) latitudes where the substorm had displaced by that time. The direction of wave-polarization vector rotation was opposite for auroral and subauroral latitudes, but it was identical at the equator and in the subauroral zone. The pulsation amplitude at the equator was maximal in the night sector.     

Deterioration of eelgrass,Zostera marina L., meadows by water pollution in Seto Inland Sea,Japan

Survival of transplanted Zostera marina L. (eelgrass) and environmental conditions (water quality, bottom sediments, sedimentation on leaves and flow regime) were studied concurrently in the center, edge, and at the outside of a eelgrass meadow located in a eutrophic coastal zone in northern Hiroshima Bay, Seto Inland Sea, Japan. Eelgrass transplants at the outside of the meadow declined significantly, whereas those at the center were consistently well established. Silt content in the bottom sediments at the outside was higher than that at the center. The sediment was oxic from the surface to 2 cm deep at the center, whereas those at the edge and the outside were reductive almost from the surface. The sediment characteristics typical in eutrophic water seemed to be a factor responsible for the deterioration of eelgrass meadows. Although suspended solid concentrations in the water columns were almost the same, the amount of sediments deposited on leaves of eelgrass at the outside was higher than that at the center of the meadow. The amount of the deposition at the outside seems to be enough to inhibit photosynthesis; i.e. photosynthetic photon flux density (PPFD) available for eelgrass was only 36% of that without any deposition. The deposition in the center, however, was small enough to allow 84% of the original PPFD. Flow rates, determined at 30 cm above the bottom, a half height of average eelgrass, suggested that the rate at the outside was not enough to remove deposited sediments from the surface of eelgrass leaves. Thus, the large amount of sediment deposition caused by water pollution and/or eutrophication seemed to be another factor to inhibit the survival of eelgrass at the outside edge of the meadow.     

Illuminating and optimising a three‐dimensional model of an oil shale seam and its volume distribution using the transient electromagnetic induction method,central part of Jordan

The oil shale exploration program in Jordan is undertaking great activity in the domain of applied geophysical methods to evaluate bitumen‐bearing rock. In the study area, the bituminous marl or oil shale exhibits a rock type dominated by lithofacies layers composed of chalky limestone, marls, clayey marls, and phosphatic marls. The study aims to present enhancements for oil shale seam detection using progressive interpretation from a one‐dimensional inversion to a three‐dimensional modelling and inversion of ground‐based transient electromagnetic data at an area of stressed geological layers. The geophysical survey combined 58 transient electromagnetic sites to produce geoelectrical structures at different depth slices, and cross sections were used to characterise the horizon of the most likely sites for mining oil shale. The results show valuable information on the thickness of the oil shale seam at 3.7 Ωm, which is correlated to the geoelectrical layer between 2‐ and 4 ms transient time delays, and at depths ranging between 85 and 105 m. The 300 m penetrated depth of the transient electromagnetic soundings allows the resolution of the main geological units at narrow resistivity contrast and the distinction of the main geological structures that constrain the detection of the oil shale seam. This geoelectrical layer at different depth slices illustrates a localised oil shale setting and can be spatially correlated with an area bounded by fold and fault systems. Also, three‐dimensional modelling and inversion for synthetic and experimental data are introduced at the faulted area. The results show the limitations of oil shale imaging at a depth exceeding 130 m, which depends on the near‐surface resistivity layer, the low resistivity contrast of the main lithological units, and the degree of geological detail achieved at a suitable model's misfit value.     

Measurements of total solar radiation at Giza

Summary Records of total solar radiation on a horizontal surface has been obtained at the Agro-meteorological Station at Giza continuously since December 1, 1955 by means of a Robitzsch actinograph. The difficulties in obtaining precise measurements were described. The results of the first three years of record were discussed and summarized in tabular and graphical form. To such few years of observations, a 15 days moving average was applied. The new data were plotted so as to obtain the solar radiation pattern, which has been compared with the radiation received at the outer limits of the atmosphere and with the maximum probable radiation expected at the Station.     

重复绝对重力测量观测的滇西地区和拉萨点的重力变化及其意义

根据近年来在滇西地区和西藏拉萨绝对重力点上的一些新的绝对重力重复观测结果 ,对1990年以来在这些点上绝对重力重复观测结果进行了分析. 滇西地区的5个绝对重力观测 点的近10年的重复观测结果表明,大部分观测时段没有出现与地球动力学事件有关的重力变 化,只有丽江和洱源2个绝对重力观测点的观测结果显示丽江地震前后有变化. 为了研究该 重力变化的原因,本文正演模拟了出现重力变化期间丽江地震同震位错引起的重力变化,模 拟结果与实际观测结果有较好的一致性. 西藏拉萨近10年以来的重复观测结果给出了拉萨点 的绝对重力值以-1.82±0.9×10-8m·s-2·a-1速率下降,这从重力学 的角度反映出青藏高原的隆升. 对拉萨点的重力变化机制进行了探讨,根据印度板块与欧亚 大陆俯冲模型计算的拉萨点重力变化速率与观测到的重力变化速率较一致,表明现今拉萨地 区重力变化是由于印度板块与欧亚大陆俯冲所引起. 根据印度板块向欧亚大陆俯冲的位错模 型计算的拉萨点的重力变化与地表垂直位移的关系,将重力变化转换为拉萨点的隆升速率为 8.7mm/a.      

磁赤道处化极方法

化向地磁极(化极)是最基本的磁测资料处理方法之一,化极能消除或减少斜磁化影响,提高对磁测资料的认识程度和解释水平,对研究地壳产生的磁异常具有重要意义.但低纬度地区特别是磁赤道处,化极处理很不稳定甚至奇异,一直是位场研究的难点.针对地磁纬度较低特别是磁赤道地区磁异常化极的困难,利用从磁北极处垂直磁化向低纬度地区水平磁化方向转换稳定的特点,提出"狭义化赤"概念,并将其与低纬度磁异常"倒相"解释方法结合,提出专门用于磁赤道处化极的方法.该方法扩展了现有的化极理论,实现了磁赤道处的稳定化极.区别于目前任何方法,专门用于(近)水平磁化条件下的化极计算,具有原理简单,实现方便,收敛速度快等特点.对理论模型和实际资料计算表明这种针对磁赤道地区磁异常的化极处理方法是稳定、可靠的.     

Time effects on dynamic soil properties under random excitation conditions

Two types of clayey soils, a kaolinite and a bentonite, were tested using a resonant column apparatus under random excitation conditions. The concept of root mean square (rms) strain was utilized for the purpose of strain calculations during random loading. The conventional estimator of the transfer function was used for random vibration analysis. The effect of confinement duration (at a constant pressure) on dynamic soil properties, namely damping and shear modulus, was evaluated. The results indicate that for both cohesive soils, the effect of time was less pronounced during random vibration than sinusoidal loading at the same rms strain. This effect is however more pronounced when the peak shearing strain of sinusoidal loading is considered. Furthermore, time effects were more pronounced at low strain levels than at high strain levels.     

High-resolution Induan-Olenekian boundary sequence in Chaohu,Anhui Province

The Lower Triassic of Chaohu has been exten-sively studied owing to its classic stratigraphic se-quence formed in a unique paleogeography, very easyaccessibility and comfortable working conditions inthe area, and the Induan-Olenekian boundary stratareceived special attention in recent years to meet therequirements of defining the GSSP of the boundary.The best-studied boundary sequence in Chaohu is atthe West Pingdingshan Section, which was recom-mended as a GSSP candidate for the Induan-…     

断层衍射波及其应用ht

本文从衍射波的物理定义出发,简化了Trorey提出的断层上Kirchhoff-Helmholtz衍射方程的解法;计算了不同深度、不同测线方向下的断层衍射波理论地震图;计算了衍射波振幅谱与相位谱,给出了利用衍射波求断层位置的公式;得出了一些新的结论,通过人工地震测深与地震勘探的实例,对断层衍射波的特性有了更明确的认识。 本文的结果表明:断层衍射波发生在地球介质剧烈变化处;衍射点两侧的衍射波走时曲线呈双曲线状;波初动清晰且半周期小;其优势频率振幅谱与反射波的相同,在衍射波与反射波走时曲线相切处附近,记录图中出现衍射波最大振幅,且波反相;视断点与真实断点一般不重合。上述特点可能为判定衍射波并确定断层位置提供判据。      

Geothermal energy release at the Solfatara of Pozzuoli (Phlegraean Fields): Phreatic and phreatomagmatic explosion risk implications

The H₂O, CO₂ and H₂S outputs at the Solfatara of Pozzuoli have been measured and a map of the exhaling areas has also been made. The energy released at the surface by the fluids has been estimated to be 10¹⁹ ergs/day.The presence of aquifers at Phlegraean Fields increases the phreatic and phreatomagmatic explosion risk.Our results suggest that even if an uprising magma may interact with water at depth, an explosion could occur only at the shallow levels of a few hundred meters. Since the transfer of energy toward the surface is favoured by the presence of fractures, a detailed analysis of the deep fracture network would help to evaluate the risk levels of the various areas of Phlegraean Fields.     

The critical point and two-phase boundary of seawater, 200–500°C

The two-phase boundary of seawater was determined by isothermal decompression of fully condensed seawater in the range of 200–500°C. The pressure at which phase separation occurred for each isotherm was determined by a comparison of the refractive index of fluid removed from the top and bottom of the reaction vessel. The critical point was determined to be in the range of 403–406°C, 285–302 bar and was located by the inflection in the two-phase boundary and by the relative volume of fluid and vapor as a function of temperature. The two-phase boundary of 3.2% NaCl solution was found to coincide exactly with that of seawater over the range tested in the present study. The boundary for both is described by a single seventh-order polynomial equation. The two-phase boundary defines the maximum temperature of seawater circulating at depth in the oceanic crust. Thus the boundary puts a limit of about 390°C for seawater circulating near the seafloor at active ocean ridges (2.5 km water depth), and about 465°C at the top of a magma chamber occurring at 2 km below the seafloor.