Nonlocal response functions in processing global electromagnetic data

We discuss approaches to mapping lateral apparent conductivity variations at different periods from magnetic observatory data using multipoint transfer operators as nonlocal functions of the EM response. The multipoint operators provide correlation of three magnetic field components recorded at all observatories. The inversion procedure was applied to S_q observatory data for 1964–68 and records of 30 magnetic storms for 1957–2001. To obtain lateral conductivity patterns, data on diurnal S_q variations and global magnetic storms were processed with the spherical harmonic analysis. The same data were used to estimate the coefficients of first harmonics in the SH series of diurnal lateral variations of Earth's apparent conductivity.     

大孔隙对农田耕作层饱和导水率的影响

介绍了土壤中大孔隙流的研究,并用一种简单的方法对土壤内的大孔隙和中小孔隙的饱和导水率进行分析,同时讨论了农田耕作层大孔隙流和Darcy流饱和导水率的变异情况。     

利用RQD估算岩体不同深度的平均渗透系数和平均变形模量

渗透系数是进行裂隙岩体渗流模拟的必备参数,变形模量是工程岩体数值模拟的必备参数。大量研究中忽视了渗透系数和变形模量随深度变化这一重要规律,从而影响模拟结果的可靠性。为此,探讨了利用极易获取的RQD（岩石质量指标）资料估算不同深度的渗透系数和变形模量的可行性。通过以某花岗岩体为例,研究发现,RQD均值随深度增大,渗透系数均值随深度减小,其相关性很好。因此,利用RQD估算不同深度的平均渗透系数是可行的。根据RQD随深度的变化,利用经验公式估算了不同深度的变形模量均值和变化范围。估算得到的变形模量与实测结果基本一致。     

Upper mantle lateral inhomogeneity estimated using global MVS

We processed synchronous observatory MVS data at periods from 1.2 to 6 days to estimate lateral conductivity variations in the upper mantle. The inverse problem for depth-dependent conductivity distribution was solved using correlation of the measured surface components of the geomagnetic field. We applied spherical harmonic expansion of the complex amplitudes of time harmonics and multiple averaging of the amplitudes obtained for different SH sets. The chosen approximation approach was tested by comparing the EM field simulated for a smoothly inhomogeneous Earth with the exact forward solution. The SHA-analyzed observatory data for fifteen magnetic storms were used to map global apparent conductivity variations.     

冻土导热系数研究现状及进展

冻土导热系数是影响冻土温度及热通量变化的一个重要参数,也是研究陆地表层水热盐耦合运移的基本物理参数。根据国内外研究现状,列举了导热系数的测试方法（稳态法和瞬态法）,总结并讨论了冻土导热系数的影响因素及其变化规律,并对目前已有的导热系数计算模型进行了比较分析。现有研究认为：土壤质地、温度和含水（冰）量、孔隙度、土壤有机质等是影响冻土导热系数的主要因素,因此,冻土土导热系数随这些影响因素的变化规律方面的研究工作非常多;而关于未冻水含量、土骨架组成及冻土结构等对冻土导热系数影响的相关研究较为缺乏。通过比较分析国内外土壤热导率计算的相关模型,认为适用于常温下导热系数的模型发展趋于成熟;而现存的适用于冻土区的导热系数计算模型多以一种或几种土壤条件为前提,或者多考虑局地因素影响,模型的适用性具有局限性。考虑到多年冻土区土壤受冻融循环影响较大,以及多年冻土内部水热传输过程的复杂性,多年冻土区导热系数的计算模型仍需进一步深入研究。     

Groundwater temperature and electrical conductivity as tools to characterize flow patterns in carbonate aquifers: The Sierra de las Nieves karst aquifer, southern Spain

In carbonate massifs, flow patterns are conditioned by karstification processes which develop a conduit network and preserve low permeability microfractured blocks. The Sierra de las Nieves karst massif (southern Spain) is subjected to a given climatic and geological context, and thus it is possible to analyse the spatial and temporal variability of the water temperature and electrical conductivity at its main karst outlets, which display different responses to rainfall episodes. In this experimental field area, conduit flow and diffuse flow drainage patterns have been distinguished by combining groundwater temperature and electrical conductivity data. Both parameters show large variations in water coming from conduit flow systems and low variations in water drained by springs draining diffuse flow systems. However, groundwater temperature displays the smallest variations, which seems to indicate that this parameter is less sensitive as regards characterising the degree of karstification, which is a key question in characterising the aquifer functioning.     

Thermal focusing in complex stratigraphic regions: Lithology and porosity effects, and equivalent vertical and horizontal thermal conductivities

Thermal focusing or defocusing by spatial variations in thermal conductivity caused by lithology and porosity fluctuations impacts the mean vertical geothermal gradient, localized fluctuations in temperature, and lateral bending of heat flow lines. Using mean field renormalization techniques, in which spatial fluctuations are treated as being randomly distributed around slowly varying mean values, estimates are given of the relative importance of lithologic and porosity variations in influencing thermal focusing. It is shown that, except for massive halite and/or evaporate variations, nearly all other geological situations can be viewed as having only a slowly varying mean lithology: fluctuations in porosity dominate thermal focusing. The mean vertical geothermal gradient is shown to be decreased by roughly 5–10% (with a maximum possible decrease of 25%) by the presence of porosity variations, relative to the mean gradient that exists in the same average medium but without fluctuations in porosity. The equivalent mean vertical thermal conductivity is shown to be increased by a maximum of about 12% relative to the non-fluctuating medium case. Root mean square temperature fluctuations vary in the typical range of 3–30°C depending on the correlation length scale of the porosity fluctuations. A correlation length of 1 km produces temperature fluctuations of around 3°C. Lateral bending of heat flux lines is implied by the thermal focusing; estimates suggest a root mean square bending angle of around 8–10°, with a corresponding mean equivalent lateral thermal conductivity of around 14% of the equivalent vertical thermal conductivity. These values are sufficiently large to suggest that fluctuations in stratigraphic sequences can lead to compartmentalized domains of juxtaposed hotter and cooler sedimentary volumes, thereby impacting the regimes of hydrocarbon generation. A simple estimate suggests that the depth of the top of the oil window may be increased by up to 0.5 km by such considerations. Effects due to anisotropic thermal conductivities, temperature dependence of thermal conductivity, and anisotropic correlated behavior of porosity and lithology fluctuations, need to be investigated to assess their significance.     

Detection and characterization of hydraulically active fractures in a carbonate aquifer: results from self-potential, temperature and fluid electrical conductivity logging in the Combioula hydrothermal system in the southwestern Swiss Alps

A geophysical and geochemical study has been conducted in a fractured carbonate aquifer located at Combioula in the southwestern Swiss Alps with the objective to detect and characterize hydraulically active fractures along a 260-m-deep borehole. Hydrochemical analyses, borehole diameter, temperature and fluid electrical conductivity logging data were integrated in order to relate electrokinetic self-potential signals to groundwater flow inside the fracture network. The results show a generally good, albeit locally variable correlation of variations of the self-potential signals with variations in temperature, fluid electrical conductivity and borehole diameter. Together with the hydrochemical evidence, which was found to be critical for the interpretation of the self-potential data, these measurements not only made it possible to detect the hydraulically active fractures but also to characterize them as zones of fluid gain or fluid loss. The results complement the available information from the corresponding litholog and illustrate the potential of electrokinetic self-potential signals in conjunction with temperature, fluid electrical conductivity and hydrochemical analyses for the characterization of fractured aquifers, and thus may offer a perspective for an effective quantitative characterization of this increasingly important class of aquifers and geothermal reservoirs.     

Numerical analysis of the hydrogeologic controls in a layered coastal aquifer system, Oahu, Hawaii, USA

 The coastal aquifer system of southern Oahu, Hawaii, USA, consists of highly permeable volcanic aquifers overlain by weathered volcanic rocks and interbedded marine and terrestrial sediments of both high and low permeability. The weathered volcanic rocks and sediments are collectively known as caprock, because they impede the free discharge of groundwater from the underlying volcanic aquifers. A cross-sectional groundwater flow and transport model was used to evaluate the hydrogeologic controls on the regional flow system in southwestern Oahu. Controls considered were: (a) overall caprock hydraulic conductivity; and (b) stratigraphic variations of hydraulic conductivity in the caprock. Within the caprock, variations in hydraulic conductivity, caused by stratigraphy or discontinuities of the stratigraphic units, are a major control on the direction of groundwater flow and the distribution of water levels and salinity. Results of cross-sectional modeling confirm the general groundwater flow pattern that would be expected in a layered coastal system. Groundwater flow is: (a) predominantly upward in the low-permeability sedimentary units; and (b) predominantly horizontal in the high-permeability sedimentary units. Received, October 1996 Revised, August 1997 Accepted, September 1997     

Laboratory investigation on hydraulic conductivity changes in sands due to injection pressure increase

In this research, the hydraulic conductivity changes in uniformly graded sands, due to injection pressure increase, were experimentally evaluated using a cell-type radial model. Conducted tests, simulating variation of media permeability at different depths along a recharge well, were monitoring variations of the samples’ hydraulic conductivity at predetermined three different overburden pressures. The startup low pressure inflow was afterward altered by increasing the injection pressure up to the point at which hydraulic conductivity started to change at each run; we called it the threshold injection pressure. The corresponding hydraulic conductivity at such pressure was measured. As the increased permeability was a function of distance to the simulated recharge, it was deemed too beneficial to develop an equation to enable predicting this new hydraulic conductivity at different distances. Findings indicate that in uniformly graded sands under overburden pressure up to 68.64 kPa, the hydraulic conductivity in the threshold injection pressure—compared to its primary amount up to 45 cm from borehole wall—show a remarkable growth. However, this growth rate for greater distances up to 60 cm is negligible. Furthermore, in the threshold injection pressure, the hydraulic conductivity seems not to be time dependent. But, in constant injection pressures above the threshold injection pressure, the hydraulic conductivity shows some sort of time dependency.     

Estimating conductivity anisotropy of lower mantle from geomagnetic observatory data

Anisotropy of electrical conductivity in the lower mantle, presumably caused by phase change of dielectric magnesiowustite, can be estimated from geomagnetic records of the globally distributed geomagnetic array. The components of the conductivity tensor corresponding to the tangential components of the geomagnetic field are obtained from the magnetic mode alone recorded on the surface. Inversion by the perturbation method is applied to monthly means of geomagnetic variations along the X, Y, and Z components for the period from 1920 to 2009, borrowed from the World Monthly Means Database. The anisotropy contribution is expressed as corrections to the conductivity tensor components. The contribution of anisotropy to induction responses becomes notable for geomagnetic variations with at least decadal periods and increases with the period length.     

An unsaturated hydraulic conductivity model for compacted GMZ01 bentonite with consideration of temperature

As one of the most important properties of compacted bentonite used as buffer/backfill materials, hydraulic conductivity is influenced by various factors including temperature, microstructure and suction (or degree of saturation), etc. Based on the readily available results of both temperature-controlled water-retention tests and unsaturated infiltration tests under confined (constant volume) conditions, influences of temperature and microstructure variations on unsaturated hydraulic conductivity of the compacted Gaomiaozi (GMZ01) bentonite were analyzed. Then, a revised unsaturated hydraulic conductivity model considering temperature effects and microstructure changes was developed. With this proposed model, prediction and comparison were made on the unsaturated hydraulic conductivity of the compacted GMZ01 bentonite at 20 °C. Results show that water-retention capacity of compacted GMZ01 bentonite decreases as temperature increases and the degree of the temperature influence depends on suction. Under confined conditions, influence of hydration on microstructure of compacted GMZ01 bentonite depends on pore size. The proposed model can well describe the variations of unsaturated hydraulic conductivity with suction at different temperatures. However, further improvement of the proposed model is needed to account for the phenomenon of inter-aggregate pores clogging that occurred at the initial stage of hydration of compacted GMZ01 bentonite under confined conditions.     

Two anisotropic layers in the Slave craton

Four years of recording global earthquakes using a broadband seismometer located at the Ekati diamond mine revealed variations with earthquake azimuth in the arrival of SKS phases. These variations can be modeled assuming two distinct layers of anisotropy in the lithosphere. The lower layer probably lies in the mantle, and the anisotropy aligns with both North American plate motion and the strike of mantle structures identified by previous conductivity and geochemical analyses, at ˜N50°E. The upper layer is hypothesized to result from regional structures in the uppermost mantle and the crust; these trends are distinct from the mantle trends.     

High-temperature electrical conductivity of clinopyroxenites in relation to their genesis (Kytlym ultramafic massif of the platinum belt of the Urals)

The electrical parameters (activation energy and electrical resistance coefficient) of rock samples were measured, and the character of their distribution was established. It was revealed that variations in electrical conductivity are related to the genetic features of clinopyroxenites, which allows us to suggest their relative age.     

黄土导热系数和比热容的实验研究

首先探讨了黄土导热系数和比热容的测试方法,组装形成黄土土样试验装置。然后取扰动黄土配制不同密度、不同含水量试样进行试验,测得黄土导热系数和比热容。实验结果揭示出,在含水量一定的情况下,导热系数和比热容随密度增大而增大;在密度相同的情况下,导热系数和比热容亦随含水量的增大而增大。进一步分析得到根据土体含水量、密度确定导热系数和比热容的关系式。相对于随密度的变化,黄土导热系数和比热容随含水量的变化尤为显著,含水量变化可以引起热参数较大的变化。     

Prediction of hydraulic conductivity for soil–bentonite mixture

Owing to its low hydraulic conductivity, soil and bentonite mixture is applied as a liner material. However, the experimental determination of hydraulic conductivity, which is controlled by various physical, chemical and mineralogical factors, requires an expensive and time-consuming setup. In the present work, multigene symbolic, genetic programming was used to model functional relationships for hydraulic conductivity. The developed model was able to generalize highly nonlinear variations in data as well as predict system behavior from experimental observations. It was found that the predictions obtained from developed model agree well with experimental observations.     

Analytical solutions for consolidation aided by vertical drains

Soil disturbance caused during the installation of vertical drains reduces the in situ hydraulic conductivity of soft deposits in the immediate vicinity of the drains, resulting in a slower rate of consolidation than would be expected in the absence of disturbance. Experimental investigations have revealed the existence of two distinct zones, a smear zone and a transition zone, within the disturbed zone around the vertical drain. The degree of change in the hydraulic conductivity in the smear and transition zones is difficult to assess without performing of laboratory tests. Based on the available literature, four different profiles of hydraulic conductivity versus distance from the vertical drain were identified. Closed-form solutions for the rate of consolidation for each of these four hydraulic conductivity profiles were developed. It is found that different variations of the hydraulic conductivity profiles in the disturbed zone result in different rates of consolidation.     

天山乌鲁木齐河源1号冰川雪坑中pH值和电导率的季节变化及淋溶过程

自2002年9月14日至2004年9月28日,在天山乌鲁木齐河源1号冰川积累区雪坑中连续观测取样,频率为1次/周。对表层雪样品和粒雪坑样品的pH值和电导率进行了分析。结果表明,表层雪的pH值和电导率具有明显的季节变化趋势,与本区域的主导山谷风风向NE和ENE密切相关。在春季,由于尘暴发生频率的增加,表层雪的pH值呈现较强碱性,电导率达到最大值;在冬季,由于原生气溶胶向次生气溶胶的转化,pH值呈现较弱碱性,电导率达到最小值。在后沉积过程中（2003年10月4日至2004年9月8日）,雪坑中不同时期的pH值和电导率呈现不同的季节变化特征和淋溶过程。电导率的峰值P1进入粒雪冰的时间比与它相对应的大粒径（直径>10 μm）微粒的浓度峰值提前40天左右;在有的雪坑中,pH值和电导率的峰值出现在污化层附近,与污化层的位置有较好的一致性,说明污化层对可溶性离子的淋溶作用可能有一定的影响。相关分析表明,Ca2+是影响表层雪中pH值和电导率变化的最主要离子。     

Statistical Distributions of Hydraulic Conductivity from Reliability Analysis Data

This paper describes a first-order reliability-based analysis to identify the best-fit probability distributions for hydraulic conductivity. The analysis involved the use of existing hydraulic conductivity model developed from laboratory data and applied to lateritic soils, considering variations in soil parameters. Plots of reliability indices versus coefficients of variation were first made for hydraulic conductivity as well as for initial degree of saturation, plasticity index and clay content, considering three compactive efforts and log-normally distributed hydraulic conductivity. The traditional two-parameter log-normal distribution was compared to four alternative distributions: normal, gamma, Gumbel (extreme value type I-EVT-I) and Weibull (extreme value type III-EVT-III). The analysis showed that the Weibull and normal are the best-fit probability distributions for the hydraulic conductivity based reliability data. Hydraulic conductivities predicted from reliability analysis were used to demonstrate the possibility of applying the results obtained in this research by practising engineers. Experimentally-determined hydraulic conductivities were shown to be in good agreement with predicted values.