Electrical earth resistivity surveying for delineating the characteristics of ground water in a semi‐arid region in the Khanasser Valley,northern Syria

A resistivity survey is conducted in Khanasser Valley, a semi‐arid region in northern Syria, to delineate the characteristics of ground water affected by the salt‐water intrusion related to Al‐Jaboul Sabkha. Existing wells were used to measure salinity and conductivity of water samplings. Vertical electrical sounding was carried out near the existing wells. The combination of resistivity and hydrogeological data enables the establishment of empirical relationships between earth resistivity, water resistivity, and the amount of total dissolved solids. These relationships are then used in order to derive salinity maps for electrode spacings of 70, 100, and 150 m. The distribution of fresh, brackish and salt‐water zones and their variations in space along two longitudinal profiles (LP1 and LP2) are established through converting subsurface depth–resistivity models into different ground‐water areas. The constructed ground‐water area maps allow interfaces between different water zones to be determined. Copyright © 2006 John Wiley & Sons, Ltd.     

地震地电阻率法的统计预报研究

系统整理了全国台网地电阻率观测资料，经预处理排除一切可能的干扰影响后，研究了地电阻率变化与地震的对应情况。共提取了４３次震例异常。研究了这些异常与地震之间的关系，给出了预报地震３要素的统计结果，为地电阻率预报地震提供了较为实用的定量指标     

THE USE OF A SQUARE CONFIGURATION IN RESISTIVITY PROSPECTING *

Consideration is given to the use of a configuration of four electrodes set in a square array for resistivity measurements. It is found that, by passing current successively between different pairs of electrodes, an apparent resistivity can be determined which is both more sensitive to the position of the array centre and less dependent on orientation than the measures usually obtained with colinear arrays of electrodes. At the same time the observations made enable the degree of the departure of local conditions from conditions of lateral homogeneity to be assessed. Theoretical and practical examples of the use of this electrode system are given and the use of the system both as a tool in mapping and in depth investigations is considered. It is shown that provided electrode spacings are suitably arranged the results of a probe carried out using the square array can be interpreted by conventional methods. The system is shown to have particular advantages in the investigation of lateral resistivity variations and the reduced dependence on orientation makes possible the recasting of interpretation data in an orientationally invariant form with a consequent drastic reduction in the number of type curves required for a particular problem.     

APPLICATION OF THE MULTIFREQUENCY HORIZONTAL-LOOP EM METHOD IN OVERBURDEN INVESTIGATIONS1

In recent years, geophysical methods (shallow seismic, electromagnetic, resistivity, ground penetrating radar) have been increasingly applied to overburden investigations. Their effectiveness has been found to depend significantly on local geological conditions. Compared with advanced seismic techniques, EM methods are faster and hence more cost-effective, but they have not been considered sufficiently accurate. Analysis is carried out of data obtained with the multifrequency horizontal-loop method (HLEM) in northeastern Ontario, where the overburden consists of Quaternary glacial and glaciolacustrine sediments. Surveying along 1-6 km long profiles permitted recognition of bedrock inhomogeneities and selection of sites suitable for HLEM data interpretation using the layered model. Phasor diagrams and computer inversion based on the ridge regression technique were used to interpret HLEM soundings obtained at eight frequencies. Interpreted layer resistivities and thicknesses were correlated with the results of Rotasonic drilling at 70 sites. Relatively accurate estimates of overburden thickness (within 10%) could be obtained in about 80% of the cases. Nine examples of HLEM soundings are given and discussed: three each of one-, two- and three-layer situations. An appropriate interpretation model cannot be selected simply by minimizing the rms error or by analysing the parameter resolution matrix. Frequently, the most effective way of evaluating a solution is to consider whether resistivity values determined by inversion fit any of the ranges determined by statistical analyses of sediment resistivities. A previously published study of electrical properties of Quaternary sediments indicated that resistivities of clay, till and sand are stable within a fairly large area, such as the one under investigation. While the application of HLEM methods to mapping of Quaternary sediments can be considered a success, interpretation of EM data in regions covered by glacial sediments is more difficult than in weathered terrains, where near-surface layering is more predictable. The problem of equivalence causes non-uniqueness in interpretation. Thickness equivalence, which results in poor resistivity estimates, was found to affect areas convered by sand and till. Conductance equivalence caused poor resolution of thickness and resistivity for thin clay layers (less than 10 m).     

地电阻率正常变化的初步研究

观测地壳浅层电阻率随时间变化以寻找地震信息是地电阻率方法的目的。实际工作中,在保证观测精度的前提下,发现正常（无震）情况的地电阻率仍然存在着复杂的变化,给定量和定性分析地震异常带来相当大的困难。 本文分析了一些台站正常地电阻率的变化规律,并在此基础上提出“变化电性剖面模式”,来阐明一些台站正常地电阻率变化的复杂过程及其产生的可能原因。从此观点出发,导出以二层电性剖面为特征的台站正常地电阻率相对似年变化幅度公式。通过典型计算,提出获取平稳的正常原始资料是解决上述困难问题的方向,并指出了获取平稳正常变化资料的具体途径。     

Electrical resistivity investigations for guiding and controlling fresh water well drilling in semi-arid region in Khanasser Valley,Northern Syria

Electrical resistivity survey is conducted in the Khanasser Valley, considered as a semi-arid region in Northern Syria, to guide and control fresh water well drilling. Vertical Electrical Soundings (VES) are carried out near the existing wells, which were also used to measure salinity and conductivity of water samplings. Resistivity and hydrogeological data combination made it possible to establish empirical relationships between earth resistivity, water resistivity, and the amount of total dissolved solids (TDS). These relationships are used in the present research in order to follow the TDS salinity variations, both in lateral and depth directions, along the longitudinal profile LP3, located in Khanasser Valley. Apparent salinity map under this profile is established for Quaternary and Paleogene deposits, and boundaries of suitable areas for fresh water well drilling in the totality of the Khanasser Valley are drawn. It was shown that excessive fresh-water depletion may affect the groundwater quality by upward seepage of saline water. Therefore, it is important to keep the fresh-salt water interface in a stationary situation. The geoelectrical methods widely contribute in determining the position of such interface, and can be easily applied in similar arid areas.     

鄂尔多斯盆地中东部长6复杂低渗储层测井评价

开展复杂低渗储层特征、测井响应及其控制因素分析,有助于储层评价与油水层识别.鄂尔多斯盆地中东部长6期沉积具多物源供给、沉积相带频繁变化的特点,来自不同物源的沉积砂体岩石碎屑成分存在明显差异.长7、长6沉积期盆地周边的火山作用,致使一些地区的长6砂体具有相对高放射性特征.长6储层孔隙类型多样,孔隙结构特征复杂多变,再加上地层水系统的变化,致使一些油区长6低电阻率油层与常规油层、高电阻率水层与常规水层共存.研究结果表明,成藏动力与阻力的对比关系决定了在同一砂体中除存在常规油水分布外,还可能存在油水倒置分布.因此,加强钴前预测、钻井过程监督与调整、钻后综合研究、生产实践检验、解释模型与参数调整、老井复查等,有利于识别油水层,整体把握油水分布规律.     

半空间中多个三维体电阻率响应的边界积分方程模拟

研究半空间中含多个异常体的复杂条件下电阻率响应数值模拟的理论和计算方法．以半空间中含两个异常作为例，导出了点源激励下地表电位分布所满足的边界积分方程组，将方程组离散化可计算出地表电位分布，从而进行视电阻率模拟．最后给出了算例．     

THE REDUCTION OF LATERAL EFFECTS IN RESISTIVITY PROBING*

To be able to make use of all existing probe interpretation techniques, it is desirable that field resistivity observations be conducted in such a way that it is possible to construct an equivalent curve for the surface variation of potential about a point source. Further, the usual parallel layer interpretation will only be justified in as much as the observed potential curve is compatible with such a subsurface geometry. Thus, whilst a potential curve may be constructed from suitable finite potential differences obtained using a Wenner configuration of electrodes, it can be shown, using the tri-potential technique of measurements, that these potential differences may arise partly from lateral resistivity variations. In this paper, a ladder network technique is employed to display these lateral effects and an adjustment method proposed to reduce them. The adjusted potential differences obtained form a consecutive series suitable for summation to give the potential function. These values are subject to further minimum adjustments required for them to comply with slope and curvature conditions for a layered medium. After forming the potential curve by summation, a final numerical smoothing process is carried out. From this smoothed potential curve, corresponding Wenner and Schlumberger curves can readily be derived for interpretation. The method proposed thus attempts to extract from the observed data the maximum part which can be reconciled with a purely depth variation of resistivity. A method is also proposed for compounding the ‘errors of closure’ of the network to provide a Lateral Inhomogeneity Index which gives a measure of the departure of the observed data from the basic interpretation requirements. The method involves no great labour, but can readily be programmed for a computer if desired. Examples are given of the application of the method to field observations. In the interest of objectivity, the final smoothing has been confined to a single stage but in certain very extreme examples a further stage may prove desirable.     

THE WATER-TABLE AQUIFER IN THE EASTERN COASTAL AREA OF BELGIUM

Abstract

A resistivity survey in Wenner arrangement has been conducted in the water-table aquifer in the eastern part of the Coastal Area of Belgium. Bore holes have been drilled to test the geoelectrical data and also to collect water samples. The chemical characteristics and the distribution of different water types explain the hydrochemistry of the water-table aquifer. The fresh-/brackish-water boundary as determined by the resistivity survey has been expressed in terms of total dissolved-solids content.     

Evaluating ground water-sea water interactions via resistivity and seepage meters

We investigated submarine ground water discharge and salt water-fresh water interactions at two locations along the shoreline of the Upper Gulf of Thailand to evaluate mechanisms of water and material transport into the coastal zone. Our data set illustrates the value of using a combined approach consisting of automatic seepage meters to monitor flow rates while assessing the conductivity (salinity) of the subterranean fluids via remote resistivity measurements. Negative correlations between electric conductivities of fluids measured directly inside seepage meter chambers and the remotely assessed resistivities of subsurface pore water show that such measurements may evaluate the spatial distribution of flow rates as well as the subterranean water quality in the coastal zone. Combined seepage and resistivity measurements may thus provide a more complete understanding of coastal ground water dynamics.     

关于非均匀介质中电导率按深度变化时的势及其视电阻率函数

本文共分六部分内容。在前言中,简述了电测深方面有关研究的情况,尤其叙述了E.S.Sampaio（1976）的结果。 因本文采用的方法不同,从而求解了适合要求的微分方程定解问题,获得了电导率以 （其中α、σ₀、σ₁均为正实数,β为实数）按深度变化时势的分布。 其次,当β=0时,对电导率σ=（σ₀+σ₁z）^α按深度变化时势的分布,应用Bessel函数的积分表达时,明显地改进和推广了E.S.Sampaio（1976）结果中的重要部分。 最后,结合实际作出了第一类、第二类标准化视电阻率函数。这种视电阻率函数,推广了Wenner和Schlumberger分别作出的视电阻率函数的有关部分,对电阻率法和激发极化法,都有其理论价值和实际意义。     

MATRIX METHOD FOR THE TRANSFORMATION OF RESISTIVITY SOUNDING DATA OF ONE ELECTRODE CONFIGURATION TO THAT OF ANOTHER CONFIGURATION1

Matrix equations are derived to transform the resistivity sounding data obtained in one type of a four-electrode array to the corresponding resistivity sounding data that would be obtained using a different four-electrode array. These expressions are based primarily on recent work in which we have established a linear relation between the apparent resistivity and the kernel function by using a powerful exponential approximation for the kernel function. It is shown that the resistivity sounding data of two different four-electrode arrays have a linear relation through an essentially non-singular matrix operator and, as such, one is derivable from the other for a one-dimensional model and it can also be extended to two-dimensions. Some numerical examples considering synthetic data are presented which demonstrates the efficiency of the method in such transformations. Two published field examples are also considered for transformation giving a reliable interpretation.     

北京市区小区域地震影响

文中研究了北京及其周围地区的历史地震和地震地质资料,并在此基础上估计了基岩运动的参数。众所周知,局部地质、地形和土质条件等许多因素对给定场地的地面运动特性都是有影响的。本文着重考虑了土层的特性对地面运动的影响.作为分析工作的基础,我们研究了北京地区典型土层的动力特性。为了分析市区各场地上的地震反应,我们将它分成面积大体相等的许多网格,对于每一网格都分析了相应土层柱状在指定输入运动下的地震反应,通过电子计算和绘图装置将结果用许多图件表示,从而给出了不同场地上地震反应谱和强震地面运动的地区分布。这些图件可用来作为制定土地利用和防震规划的参考。我们根据市区每一地点的计算反应谱和典型结构的平均周期确定了相应结构的地震系数,结果已绘成等值线,这些图件可作为典型结构的震害预测和抗震设计的参考。      

Mapping multi‐year ground water salinity patterns in irrigation areas using time‐series analysis of ground water salinity maps

In irrigation areas, ground water salinity (GWS) levels may vary depending on the amount and quality of irrigation water applied and on the activity of the drainage system. GWS plays a vital role in irrigation systems by influencing whether the environment is suitable for plant growth. Hence, it is necessary to monitor changes in GWS both temporally and spatially. Maps are generally used to visualize this information. However, evaluation of temporal and spatial variations of GWS can be difficult because of the necessity of assessing many maps together to understand both temporal and spatial changes. In this study, a data assessment method that can be used for multi‐year ground water salinity evaluations is presented. The method looks at the spatial and temporal relationships between the main salinity classes present in the study area, their typical locations (i.e. areas where the salinity classes are most frequently located), and the alternate salinity classes in those locations in any of the years of the time series. As a case study, the method was applied to multi‐year (1990–2000) GWS observations in the Mustafakemalpasa irrigation project (19 370 ha) in the Marmara region of north‐western Turkey. Copyright © 2007 John Wiley & Sons, Ltd.     

清水地震台地下流体观测资料的分析应用

清水地震台目前有3个测点,有流量、水氡、水位、水温4种手段（5个测项）,是数字和模拟观测同时进行的地下流体综合观测台。通过对该台各种资料的分析发现,流量观测资料在甘肃及邻区多次中强震之前出现明显的高值异常;水氡观测资料也有异常出现。自1999年之后,水氡测点附近地区由于大量开采热水,对观测资料造成明显干扰;水位观测资料除记录到较明显的固体潮现象外,还记录到大震的同震效应;水温观测资料也记录到某些大震的同震效应。     

Important observations and parameters for a salt water intrusion model

Sensitivity analysis with a density-dependent ground water flow simulator can provide insight and understanding of salt water intrusion calibration problems far beyond what is possible through intuitive analysis alone. Five simple experimental simulations presented here demonstrate this point. Results show that dispersivity is a very important parameter for reproducing a steady-state distribution of hydraulic head, salinity, and flow in the transition zone between fresh water and salt water in a coastal aquifer system. When estimating dispersivity, the following conclusions can be drawn about the data types and locations considered. (1) The "toe" of the transition zone is the most effective location for hydraulic head and salinity observations. (2) Areas near the coastline where submarine ground water discharge occurs are the most effective locations for flow observations. (3) Salinity observations are more effective than hydraulic head observations. (4) The importance of flow observations aligned perpendicular to the shoreline varies dramatically depending on distance seaward from the shoreline. Extreme parameter correlation can prohibit unique estimation of permeability parameters such as hydraulic conductivity and flow parameters such as recharge in a density-dependent ground water flow model when using hydraulic head and salinity observations. Adding flow observations perpendicular to the shoreline in areas where ground water is exchanged with the ocean body can reduce the correlation, potentially resulting in unique estimates of these parameter values. Results are expected to be directly applicable to many complex situations, and have implications for model development whether or not formal optimization methods are used in model calibration.     

Seawater intrusion and fresh groundwater hydraulics in fjord delta aquifers inferred from ground penetrating radar and resistivity profiles—Sunndalsøra and Esebotn, western Norway

Geophysical surveys have been carried out in two fjord delta aquifers in western Norway. Geophysical methods comprised ground penetrating radar (GPR), shallow reflection seismic and resistivity measurements. The purpose of the investigations was to evaluate hydrogeological properties of the fjord delta aquifers with emphasis on the possibilities of abstracting saline groundwater for use in fish farming. At Sunndalsøra, reflection seismic was helpful in the mapping of the base of the aquifer. Resistivity profiles revealed both the spatial and seasonal variability of seawater intrusion. Penetration depths of ground penetrating radar (GPR-D) revealed the spatial variation of the boundary of the transition zone between saline and fresh groundwater. Maps of GPR-D can be used to indicate direction and magnitude of mean hydraulic gradients and thus to locate optimal sites for both fresh and saline groundwater abstraction.In fjord delta aquifers, both rivers and abandoned river channels constitute important groundwater divides. Optimal locations for saline groundwater abstraction wells are in areas separated from the rivers by abandoned river channels. In areas between the rivers and the abandoned river channels, groundwater abstraction will result in decreasing salinity of the water.     

Extending electromagnetic methods to map coastal pore water salinities

The feasibility of mapping pore water salinity based on surface electromagnetic (EM) methods over land and shallow marine water is examined in a coastal wetland on Tampa Bay, Florida. Forward models predict that useful information on seabed conductivity can be obtained through <1.5 m of saline water, using floating EM-31 and EM-34 instruments from Geonics Ltd. The EM-31 functioned as predicted when compared against resistivity soundings and pore water samples and proved valuable for profiling in otherwise inaccessible terrain due to its relatively small size. Experiments with the EM-34 in marine water, however, did not reproduce the theoretical instrument response. The most effective technique for predicting pore water conductivities based on EM data entailed (1) computing formation factors from resistivity surveys and pore water samples at representative sites and (2) combining these formation factors with onshore and offshore EM-31 readings for broader spatial coverage. This method proved successful for imaging zones of elevated pore water conductivities/salinities associated with mangrove forests, presumably caused by salt water exclusion by mangrove roots. These zones extend 5 to 10 m seaward from mangrove trunks fringing Tampa Bay. Modeling indicates that EM-31 measurements lack the resolution necessary to image the subtle pore water conductivity variations expected in association with diffuse submarine ground water discharge of fresher water in the marine water of Tampa Bay. The technique has potential for locating high-contrast zones and other pore water salinity anomalies in areas not accessible to conventional marine- or land-based resistivity arrays and hence may be useful for studies of coastal-wetland ecosystems.     

USE OF ELECTRICAL RESISTIVITY METHODS FOR THE STUDY OF COAL SEAMS IN PARTS OF THE RANIGANJ COALFIELD (INDIA)*

The surface resistivity method has been used to study a few exposed coal seams located in the northwestern part of the Raniganj Coalfield (belonging to the Damodar Valley Gondwana basin), India. Different electrode configurations, viz., Wenner, two-electrode and half-Schlumberger, have been used with different electrode spacings in horizontal profiling. The vertical distribution of resistivity has been studied using Schlumberger configuration at different locations along the profile. Laboratory studies of resistivity (at partial to full water saturation conditions) and porosity of different coal, shaly sandstone and sandstone samples of the survey area had already been carried out before the field survey. The results indicated the presence of a good resistivity contrast between the coal seams and the surrounding formations. The field results did not bear this out: the resistivity responses of the coal formations on the profiles and sounding curves are not as clear as one would expect for such high contents. The Wenner profiles show a broad resistivity anomaly over the coal seams. Two-electrode profiles are less noisy than Wenner profiles. Sharp peaks have been observed over the coal seams. The half-Schlumberger configuration seems the best: all the coal seams and their edges can be accurately outlined on the resistivity curves. Borehole data close to the profile have been used for correlating the field results. There is good agreement with vertical electrical soundings.