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1.
PROSPECTING FOR SUBSURFACE WATER IN THE CENTRAL VOLCANIC HIGHLAND OF ARMENIA BY GEOPHYSICAL METHODS*
R. S. MINASIAN 《Geophysical Prospecting》1979,27(4):808-814
Work carried out in several volcanic areas in Armenia has led to a combination of geophysical methods for hydrogeological problems. Prospecting of interlava and sublava water flows is done by electrical profiling and vertical electrical sounding. When mapping the relief of sublava water-resisting rocks, the electrical sounding (ES) method is widely used. This is based on the evaluation of lava resistivity. The method discussed allows to determine the most probable value of this parameter, by using statistical methods. 相似文献
2.
The results of geophysical surveys carried out in the Kopili Hydel Project site in the United North Cachar and Mikir Hills district, Assam, to locate and trace underground caverns in limestone are presented. Electrical resistivity observations over known limestone caverns showed significant anomalies (high resistivity). In the course of the systematic electrical resistivity survey conducted at the eastern fringe of the Umrong basin to study the competency of the proposed reservoir, a number of indications of possible caverns in limestone were obtained and a few of them have been verified by drilling. An analysis of the electrical resistivity data also suggests that the deep seated caverns are aligned along an axis trending NNW-SSE, which may represent a zone of weakness– presumably a fault–that has influenced the formation of the caverns in preferred direction. Drilling over a few of the geophysical indications have corroborated the presence of a fault along the eastern fringe of the Umrong basin. 相似文献
3.
地震勘探方法是隐伏断层探测的一种有效的地球物理探测手段,而地震勘探的探测参数是影响探测效果和断层定位精度的主要因素.本文以银川市活断层探测的浅层地震勘探资料为例,并结合石油地震勘探剖面结果和钻孔地质资料,阐述了在第四纪覆盖层较厚的地区,由深至浅追踪目标断层形态和确定断层上断点空间位置的方法技术.结果表明,采用高分辨率地震勘探和钻孔地质剖面相结合的探测方法是确定隐伏断层位置、判定断层活动性的有效方法. 相似文献
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5.
A combination of DC-resistivity sounding and profiling measurements can be used to obtain the maximum information about distribution of resistivities in the earth. Combined sounding-profiling measurements with the AMN, MNB arrays are considered. The resistivity data from such measurements can be presented as: (a) normal sounding curves, (b) combined sounding-profiling curves, (c) profiling curves, (d) pseudo-sections, or as transformations obtained by the so-called gradient processing, to emphasize the influence of the target objects. The examples chosen from numerical modeling and field tests show the efficiency of measurements with three-electrode arrays to accurately locate thin conductors and contacts of lithological units of different resistivities. An interpreted cross-section is compared with the results of other geophysical measurements (VLF-R, dipole EM, Δ, IP) showing good correlation. 相似文献
6.
A combination of geophysical methods including continuous electrical resistivity and high-resolution Chirp sub-bottom profiling were utilized to characterize geologic controls on pore fluid salinity in the nearshore of Long Bay, SC. Resistivity values ranged from less than 1 Ω m to greater than 40 Ω m throughout the bay. Areas of elevated electrical resistivity suggest the influence of relatively fresher water on pore water composition. Geophysical evidence alone does not eliminate all ambiguity associated with lithological and porosity variations that may also contribute to electrical structure of shallow marine sediments. The anomalous field is of sufficient magnitude that lithological variation alone does not control the spatial distribution of elevated electrical resistivity zones. Geographical distribution of electrical anomalies and structures interpreted from nearby sub-bottom profiles indicates abrupt changes in shallow geologic units control preferential pathways for discharge of fresh water into the marine environment. Shore parallel resistivity profiles show dramatic decreases in magnitude with increasing distance from shore, suggesting a significant portion of the terrestrially driven fresh SGD in Long Bay is occurring via the surficial aquifer within a few hundred meters of shore. 相似文献
7.
Tomá? Fischer Petra ?těpan?íková Magda Karousová Petr Tábo?ík Christina Flechsig Mahmoud Gaballah 《Studia Geophysica et Geodaetica》2012,56(4):1019-1036
Geodynamic activity in the area of West Bohemia is typified by the occurrence of earthquake swarms, Quaternary volcanism and high flux of mantle-derived CO2. The highest swarm activity occurs beneath the eastern edge of the Cheb basin, which is delineated by the NW-SE trending morphologically pronounced Mariánské Lázn?? Fault (MLF) controlling the formation of the basin. The previous trenching survey across the MLF zone has identified several fault strands with possible Quaternary activity. In this paper we present the results of the geophysical survey focused to trace the faults signatures in geophysical sections and to build an image of near surface tectonics. The method of electric resistivity tomography (ERT) along two profiles parallel to the trench identified a strong resistivity contrast between the bodies of sandy gravels in the middle and conductive clayey sands to the west and weathered crystalline basement to the east. The 2-D ground penetration radar (GPR) sections show direct correlation of reflections with lithological boundaries identified in the trench. As expected, the GPR signal amplitudes increase with the resistivities found in the ERT sections. Two of the four faults identified in the trench are indicated in the resistivity and GPR sections. A 3-D GPR measurement has identified a spot of high amplitudes elongated parallel to the MLF trend, which coincides with the high resistivity body. To improve the signal-to-noise ratio of the time slices we stacked the GPR time slices within vertically homogeneous blocks. This provided a contrast image of the sand-gravel body including its boundaries in three dimensions. The detailed analysis of the 3-D GPR cube revealed additional fault that limits the highly reflective sands and appears to be offset by another younger fault. Our results suggest a complex fault pattern in the studied area, which deserves a further study. 相似文献
8.
高密度电法CT成像技术在活断层探测中的应用 总被引：12，自引：0，他引：12
高密度电法CT成像技术近年来在工程物探上得到了广泛应用，已成为工程物探的一种主要方法之一，本文在无棣一益都断裂的活动性研究中，运用该方法取得了良好效果。这一工程实例表明利用高密度CT成像技术，辅以地质钻探，可以较精确地探测断裂活动的具体空间形态等，为开展大城市活断层探测与研究，进行合理城市规划和抗震设防提供依据。 相似文献
9.
CORRELATION BETWEEN GAS GEOCHEMICAL EMISSION AND FAULT ACTIVITY OF THE YUXIAN-GUANGLING AND KOUQUAN FAULTS 
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下载免费PDF全文 Soil gas emission is closely related to tectonic and seismic activity and has been widely used to track active faults and monitor seismicity in the upper crust. Because active fault plays an important role as the channel of the earth's deep gas upward migration due to its high permeability and porosity, the geochemical characteristics of soil gas in fault zone is a good indicator of tectonic fracture and activity. In order to study the soil gas geochemical emission intensities and its correlation to fault activity, fluxes of Rn, Hg and CO2 in soil gas and the ground resistivity were surveyed across the Yuxian-Guangling Fault and Kouquan Fault which are both Quaternary active faults in the border area of Shanxi Province, Hebei Province and Inner Mongolia Autonomous Region. In 2017, soil gas fluxes were measured in 2 profiles consisting of 10 and 9 wells of depth of 3.0m across the fault scarps in Yuxian-Guangling Fault and Kouquan Fault, respectively. Resistivity tomography sections were attained by ground resistivity survey with electrode spacing of 5.0m along the profiles of soil gas measurement. The gas geochemical data show that there exist two abnormal flux peaks across the Yuxian-Guangling Fault and one in the Kouquan Fault. The high density resistivity measurement shows that fault breccia and fractured rocks zones are developed under the measured faults, where higher values of soil gas flux are also observed. Fractures with high gas permeability in the strata favor the transfer and migration upward of soil gases, which results in the anomalies of gas flux value. In addition, the anomalies of gas flux values are spatially identical with the occurrence of the fault scarps. The soil gas degassing rate of Yuxian-Guangling Fault is higher than that of Kouquan Fault. The research results of high density electrical prospecting and previous tectonic activity show that low-resistance bodies are more developed and the fault activity is stronger with higher slip rate, which leads to the more intense emission of soil gas in Yuxian-Guangling Fault. The conclusions can be made that soil gas geochemical characteristics and degassing rate in fault zone is closely correlated to the tectonic activity and fracture degree. Combination of geochemical and geophysical methods is an efficient way for the monitoring and study of fault activity to estimate the possible earthquake hazards. 相似文献
10.
利用黄海海区重磁观测数据,以最新的地震层析成像和浅层反射地震探测结果作为约束,并利用小波分解、纹理特征图像处理等手段,对研究区进行了地球物理场特征分析、岩石物性总结、断裂信息提取和磁性基底埋深反演计算,同时对南黄海海域三条剖面进行了广义逆重磁数据拟合反演和地震P波速度成像.根据地球物理数据的各种处理结果,提出在南黄海西部存在一条串珠状地球物理线性构造带,并将这条NNW向断续延伸的构造带称之为南黄海西缘断裂带.该断裂带延伸长,断裂两侧前新生代地层差异较大,有可能是造成陆区和南黄海南部盆地区前新生代油气远景差异的原因之一.文中得到南黄海磁性基底埋藏分布具有“中间浅四周深”的分布特征,与地震层析成像结果相吻合.磁性基底的局部起伏和局部构造的边界断层共同控制了前新生代残留盆地的格架和残余厚度分布,反映出“区域控制局部,深层约束浅层”的规律. 相似文献
11.
The thicknesses of slag piles at a smelling site in Midvale. Utah, were determined using geophysical methods; this information was needed to estimate the cost of removing or isolating slag that has the potential to contaminate ground water. From a small-scale preliminary investigation that, included terrain-conductivity profiling, low-frequency resistivity measurements, and induction logging, the electrical resistivities of the slag and the underlying sediment were determined to be approximately 100 Ω-m and 15 Ω-m, respectively. Because electromagnetic measurements are affected by such significant contrasts, terrain-conductivity profiling and time-domain electromagnetic soundings were used to determine the thicknesses of the slag piles. Generally, the estimated thicknesses from both methods were consistent and geologically plausible. In some instances, reliable estimates of the thicknesses could not be obtained because, for example, the measurements were affected by buried metal objects.
In this case study, we emphasize three principles that might help investigators at other smelter sites. First, a small-scale preliminary investigation saves time and money because those geophysical methods that have the greatest likelihood of success can be determined. Second, when the results from several geophysical methods are consistent, the confidence in the interpretation increases. Third, geophysical characterization is not always successful. Nonetheless, because of its outstanding advantages, it should be used before other more expensive characterization methods arc tried. 相似文献
In this case study, we emphasize three principles that might help investigators at other smelter sites. First, a small-scale preliminary investigation saves time and money because those geophysical methods that have the greatest likelihood of success can be determined. Second, when the results from several geophysical methods are consistent, the confidence in the interpretation increases. Third, geophysical characterization is not always successful. Nonetheless, because of its outstanding advantages, it should be used before other more expensive characterization methods arc tried. 相似文献
12.
A fault zone, inferred as a major linear structure from aerial photographs of the University of Ife Campus, has been investigated. Results of a multi-method geophysical survey indicate that the zone is characterized by relatively low resistivity and high magnetic effect. They are characteristic of a sheared and perhaps saturated fault zone with magnetic mineral infillings along its plane. The near symmetry of the magnetic anomalies over the fault zone may not be indicative of a step faulting. The geoelectric sections show no indication of any significant displacement. The above supports results of a previous study that the fault is a strike-slip fault. 相似文献
13.
The latent impact of the Ghab pull-apart basin tectonic setting and associated deformations resulting from active tectonics on the Qastoon Dam in northern Ghab in Syria have been evaluated. This was achieved by applying an appropriate methodology essentially based on morphotectonic mapping and integrated geophysical surveys consisting of electrical resistivity profiling, vertical electrical sounding and self-potential. The integrated interpretation of the acquired morphotectonic and geophysical data allowed the detection of subsurface deformed structures, either underlying the Qastoon Dam lake floor, or close to it. It is believed that these active structures were developed through the ongoing active tectonic processes occurring in the Northern Arabian plate. The tectonic survey proved that the N66.5°E striking Wadi Al Mashta fault, extending beneath the Qastoon Dam lake floor, is one of the youngest active structures, and that the intersection of the fault with the Qastoon Dam prism is a water-leaking point. Dam supporting measures, continuous monitoring and precautious disaster management are therefore recommended to be urgently adopted and practiced. 相似文献
14.
阿尔金断裂带东段走滑速率沿断裂走向方向存在明显的流失现象,有关阿尔金断裂带的影响范围及走滑速率变化的机制需要有更多的深部结构证据来提供支撑.本文以阿尔金断裂带昌马段为窗口,获取了4条横穿阿尔金断裂带及相邻地区的大地电磁测深剖面.二维电性剖面显示在阿尔金断裂带北侧中上地壳以连续的高阻体为主,而南侧祁连山内部的深部电性结构在横向上有较为复杂的变化.这一点与区域构造背景相对应,即北侧的塔里木盆地东缘依然具有较好的整体性,南侧的祁连山是青藏高原北缘生长的最前端,变形强烈.在断裂带的结构特征上,阿尔金断裂带沿走向方向的切割深度在昌马盆地西侧发生了显著的降低,与阿尔金断裂带相对应的电性边界在这里向南偏移了约15 km,对应F18断裂,并与昌马盆地相接.祁连山北部的断裂带,包括昌马断裂、旱峡—大黄沟断裂总体呈现出低角度南倾的样式,切过高阻异常体的顶部.虽然昌马盆地可以起到连接断裂带的阶区的作用,将部分阿尔金断裂的走滑分量转移到盆地南侧的昌马断裂上,但是昌马断裂的走滑速率从西向东是增加的,东侧的走滑速率甚至大于阿尔金断裂沿走向方向的流失分量.我们认为在青藏高原北部主要断裂带的活动还是受印度—欧亚板块碰撞引起的远程挤压效应的影响,包括阿尔金断裂以及祁连山内部系列断层都处于斜向挤压应力环境.在这种基本构造模式下,阿尔金断裂、断裂F18、昌马盆地、昌马断裂构成了一个局部的走滑速率分解-转换-吸收体系,对局部应力状态产生影响. 相似文献
15.
Raghu K. Chunduru Mrinal K. Sen Paul L. Stoffa R. Nagendra 《Geophysical Prospecting》1995,43(8):979-1003
The inversion of resistivity profiling data involves estimation of the spatial distribution of resistivities and thicknesses of rock layers from the apparent resistivity data values measured in the field as a function of electrode separation. The drawbacks of using traditional curve-matching techniques to solve this inverse problem have been overcome by iterative linear techniques but these require good starting models even if the shape of the causative body is asssumed known. In spite of the recent developments in inversion techniques, no robust method exists for the inversion of resistivity profiling data for the simple model of dikes and spheres which are the classical models of geophysical prospecting. We apply three different non-linear inversion schemes to invert synthetic resistivity profiling data for the classical models embedded in a uniform matrix of contrasting resistivity. The three non-linear algorithms used are called the Metropolis simulated annealing (SA), very fast simulated annealing (VFSA) and a genetic algorithm (GA). We compare the performance of the three algorithms using synthetic data for an outcropping vertical dike model. Although all three methods were successful in obtaining optimal solutions for arbitrary starting models, VFSA proved to be computationally the most efficient. 相似文献
16.
Resistivity in horizontal boreholes can give useful detailed information about the geological conditions for construction in rock, i.e. in front of a tunnel bore machine. This paper is an attempt to identify a suitable methodology for an effective measuring routine for this type of geophysical measurements under actual construction site conditions.Prior to any measurements numerical modelling was done in order to evaluate the resolution of different electrode arrays. Four different arrays were tested; dipole–pole, cross-hole dipole–dipole, cross-hole pole–tripole and multiple gradient array. Additionally the resolution of a combination of cross-hole dipole–dipole and multiple gradient was assessed. The 2D sensitivity patterns for various arrangements of the cross-hole dipole–dipole and multiple gradient array were examined. The sensitivity towards inaccurate borehole geometry and the influence of water in the boreholes were also investigated. Based on the model study the cross-hole dipole–dipole array, multiple gradient array and a combination of these were found to give the best result and therefore were used for test measurements in horizontal boreholes. The boreholes were 28.5 m long and drilled 6.5 m apart. Prototypes of semi-rigid borehole cables made it possible to insert multi electrode cables in an efficient way, allowing fast measurement routines. These measurements were then studied to determine their accuracy and applicability. The results showed a high resistivity rock mass at the site. A transition from high resistivity to slightly lower resistivity coincides well with a change in lithology from gneiss-granite to gneiss. It is likely that the shotcrete on the tunnel wall is seen as a low resistivity zone.The measurements are a valuable tool, but further development of the cables and streamlining of measuring routines have to be performed before the resistivity tomography can be used routinely in pilot holes during construction in rocks. 相似文献
17.
P. P. G. Bruno V. Paoletti M. Grimaldi A. Rapolla 《Journal of Volcanology and Geothermal Research》2000,98(1-4)
Integrated geophysical surveys were performed in two sites, Fossa di Fuardo and Terme di San Calogero in Lipari Island, Southern Italy with the intent of the exploration of low-enthalpy geothermal fluids. Both sites show strong geochemical and geologic evidences of hydrothermal activity. The geophysical methods consist of two microgravimetric surveys, two 2D geoelectric profiles, a seismic reflection profile and a five seismic refraction profiles. The seismic methods allowed us to locate the main subsurface seismic discontinuities and to evaluate their geometrical relationships. The gravity field was used to constraint the seismic discontinuities, while the electric prospecting let discriminate more conductive areas, which could correspond to an increase in thermal fluid circulation in the investigated sites.The results obtained by the different geophysical methods are in good agreement and permit the definition of a reliable geo-structural model of the subsurface setting of the two investigated areas. A low-enthalpy geothermal reservoir constituted by a permeable pyroclastic and lava sequence underlying two shallow impermeable formations was found at Fossa del Fuardo. The reservoir is intersected by some sub-vertical faults/fractures that probably play an important role in convoying the thermal water up to the surface. At the other site, Terme di S. Calogero, the geophysical surveys showed that an intense circulation of fluids affects the subsurface of the area. This circulation concentrates along a ENE-trending fault located at a little distance from the thermal resort. The hot fluids may upraise along the fault if the width of the ascent area is smaller than 20 m. 相似文献
18.
F. S. Birch 《Ground water》1984,22(4):427-432
Bedrock depths can be calculated readily from ground magnetic profiles using either Werner deconvolution or Fourier spectral analysis. For crystalline basement rocks of New England and eastern Canada, a vertical dike is a useful magnetic source model. Formulae for these methods are presented along with some practical guidelines for implementing them. Six field examples from metamorphic and igneous areas in New Hampshire show that bedrock depths from spectral analysis agree well with estimates from seismic refraction, from wells and from outcrops. The Werner estimates are much more variable but commonly bracket the others. At several of these sites, measurements by other geophysical methods would be impractical, more expensive, or restricted to certain times of the year. 相似文献
19.
USING DEFORMED FLUVIALTERRACES OF THE QINGYIJIANG RIVER TO STUDY THE TECTONIC ACTIVITY OF THE SOUTHERN SEGMENT OF LONGMENSHAN FAULT ZONE 下载免费PDF全文
下载免费PDF全文 On 20 April 2013, a destructive earthquake, the Lushan MS7.0 earthquake, occurred in the southern segment of the Longmenshan Fault zone, the eastern margin of the Tibetan plateau in Sichuan, China. This earthquake did not produce surface rupture zone, and its seismogenic structure is not clear. Due to the lack of Quaternary sediment in the southern segment of the Longmenshan fault zone and the fact that fault outcrops are not obvious, there is a shortage of data concerning the tectonic activity of this region. This paper takes the upper reaches of the Qingyijiang River as the research target, which runs through the Yanjing-Wulong Fault, Dachuan-Shuangshi Fault and Lushan Basin, with an attempt to improve the understanding of the tectonic activity of the southern segment of the Longmenshan fault zone and explore the seismogenic structure of Lushan earthquake.
In the paper, the important morphological features and tectonic evolution of this area were reviewed. Then, field sites were selected to provide profiles of different parts of the Qingyijiang River terraces, and the longitudinal profile of the terraces of the Qingyijiang River in the south segment of the Longmenshan fault zone was reconstructed based on geological interpretation of high-resolution remote sensing images, continuous differential GPS surveying along the terrace surfaces, geomorphic field evidence, and correlation of the fluvial terraces.
The deformed longitudinal profile reveals that the most active tectonics during the late Quaternary in the south segment of the Longmenshan Fault zone are the Yanjing-Wulong Fault and the Longmenshan range front anticline. The vertical thrust rate of the Yanjing-Wulong Fault is nearly 0.6~1.2mm/a in the late Quaternary. The tectonic activity of the Longmenshan range front anticline may be higher than the Yanjing-Wulong Fault. Combined with the relocations of aftershocks and other geophysical data about the Lushan earthquake, we found that the seismogenic structure of the Lushan earthquake is the range front blind thrust and the back thrust fault, and the pop-up structure between the two faults controls the surface deformation of the range front anticline. 相似文献
20.
The vadose zone is the main region controlling water movement from the land surface to the aquifer and has a very complex structure. The use of non-invasive or minimally invasive geophysical methods especially electrical resistivity imaging is a cost-effective approach adapted for long-term monitoring of the vadose zone. The main aim of this work is to know the fractures in the vadose zone, of granitic terrene, through which the recharge or preferred path recharge to the aquifer takes place and thus to relate moisture and electrical resistivity. Time lapse electrical resistivity tomography (TLERT) experiment was carried out in the vadose zone of granitic terrene at the Indian Geophysical Research Institute, Hyderabad along two profiles to a depth of 18 m and 13 m each. The profiles are 300 m apart. Piezometric, rainfall and soil moisture data were recorded to correlate with changes in the rainfall recharge. These TLERT difference images showed that the conductivity distribution was consistent with the recharge occurring along the minor fractures. We mapped the fractures in hard rock or granites to see the effect of the recharge on resistivity variation and estimation of moisture content. These fractures act as the preferred pathways for the recharge to take place. A good correlation between the soil moisture and resistivity is established in the vadose zone of granitic aquifer. Since the vadose zone exhibits extremely high variability, both in space and time, the surface geophysical investigations such as TLERT have been a simple and useful method to characterize the vadose zone, which would not have been possible with the point measurements alone. The analyses of the pseudosection with time indicate clearly that the assumption of the piston flow of the moisture front is not valid in hard rocks. The outcome of this study may provide some indirect parameters to the well known Richard's equation in studying the unsaturated zone. 相似文献