The southeastern border of the Upper Rhine Graben: a 3D geological model and its importance for tectonics and groundwater flow

A 3D geological model of the area east of Basel on the southeastern border of the Upper Rhine Graben, consisting of 47 faults and six stratigraphic horizons relevant for groundwater flow, was developed using borehole data, geological maps, geological cross sections, and outcrop data. This model provides new insight into the discussions about the kinematics of the area between the southeastern border of the Upper Rhine Graben and the Tabular Jura east of Basel. A 3D analysis showed that both thin-skinned and thick-skinned tectonic elements occur in the modeled area and that the Anticline and a series of narrow graben structures developed simultaneously during an extensional stress-field varying from E–W to SSE–NNW, which lasted from the Middle Eocene to Late Oligocene. In a new approach the faults and horizons of the 3D geological model were transferred into discrete elements with distributed hydrogeological properties in order to simulate the 3D groundwater flow regime within the modeled aquifers. A three-layer approach with a horizontal regularly spaced grid combined with an irregular property distribution of transmissivity in depth permitted the piezometric head of the steady-state model to be automatically calibrated to corresponding measurements using more than 200 piezometers. Groundwater modeling results demonstrated that large-scale industrial pumping affected the groundwater flow field in the Upper Muschelkalk aquifer at distances of up to 2 km to the south. The results of this research will act as the basis for further model developments, including salt dissolution and solute transport in the area, and may ultimately help to provide predictions for widespread land subsidence risks.     

Seasonal movement and groundwater flow mechanism in an unsaturated saprolitic hillslope

Numerous field monitoring programs have been conducted to investigate the performance of an unsaturated soil slope subjected to rainfalls in wet seasons. Most case histories focus on the response of matric suction, which is one of the two stress-state variables governing unsaturated soil behaviour. However, effects due to another variable, net normal stress, are often ignored. Also, slope performance under alternative wet and dry seasons is rarely reported and analysed. In this study, a saprolitic hillslope situated in Hong Kong was instrumented heavily to investigate its seasonal movement due to changes of the two variables and also groundwater flow mechanism. Two-year seasonal variations of matric suction and net normal stress were monitored by tensiometers together with heat dissipation matric water potential sensors and earth pressure cells, respectively. During heavy rainstorms in wet season, there was a substantial recharge of the main groundwater table, causing a significant increase of positive pore-water pressure in deeper depths. Rupture surface likely developed at depths between 5.5 and 6 m, hence resulting in a “deep-seated” mode of downslope movement. The downslope movement resulted in a peak increase of horizontal stress. In dry seasons, matric suction of up to 190 kPa was recorded, and the associated soil shrinkage led to substantial upslope rebounds. The stress built up in wet seasons hence reduced. After monitoring period of 2 years, downslope ratcheting is identified. Up to 40 % of the downslope displacements were recovered by the upslope rebounds.     

广西某锡矿地质-地球物理模型及成矿预测研究

根据广西某锡矿的矿床地质特征及地球物理特征,建立了矿区的地质-地球物理模型。结合地质-地球物理模型及CSAMT法测量结果,推断了隐伏岩体顶界面及矿化富集规律。钻孔验证结果与物探推断结果基本一致,证实了CSAMT法在本矿区深边部找矿的有效性,所建地质-地球物理模型对本矿区成矿预测具有一定指导意义。     

关于滑坡稳定性在滑坡安全系数取值中的作用讨论

在工程界存在着滑坡安全系数取值应考虑滑坡稳定性高低、对稳定系数较低的滑坡应采用较大的安全系数的思想。考虑滑坡稳定性的具体方式有两种:①考虑滑坡的实际稳定状态或变形情况;②考虑设计工况下的稳定系数。考虑滑坡稳定性的理由也有两种:①变形急剧势必危害较大;②滑坡在治理后的安全储备可用"安全储备系数"(即下滑力按安全系数放大后的剩余下滑力与下滑力不作改变时的剩余下滑力之比)来衡量,而"安全储备系数"存在着随稳定系数的减小而减小的规律。文章的研究表明,滑坡变形越急剧滑坡危害越大的规律是不存在的,滑坡"安全储备系数"既不能衡量滑坡在治理后的安全储备,也不随滑坡稳定系数的减小而减小,滑坡安全系数与稳定系数无关,将安全系数取值与稳定系数大小挂钩会导致诸多不合理现象产生。因此,滑坡安全系数取值不应考虑稳定系数大小。     

Failure and flow development of a complex slide: the 1993 Sesa landslide

Large landslides are often characterised by complex activity resulting from their ability to suddenly change behaviour. In fact, these landslides can pass from a slump to a flow characterised by relatively high mobility. This characteristic is a cause of extremely high severity and hazard in areas affected by such phenomena. An interesting case of a large slide in glacial deposits, which occurred in 1993 in the Valcamonica of the Italian Alps, is presented. Different approaches both to characterise the coarse frictional materials involved in the slide and to model the slide initiation and its evolution are adopted. The initial slide mass had a volume of almost 2 Mm³ and after its initial sliding motion along the slope, flowed for about 7 km down the main valley stream. Voight's method has been used to analyse measured slope displacements recorded for a few years before the slope failure. This analysis provided evidence that different times of failure could have been predicted beforehand by rigorous examination of the available data. Laboratory tests and image/processing techniques have been performed to characterise the landslide material as resembling a “bimrock” (block in matrix material). Slope stability analyses have been performed and a dynamic modelling method has been tested on the flow by comparing its results to those obtained by analysis of eyewitness statements and field observations on the mudline left by the flow. Finally, existing empirical approaches for hazard assessment on an alluvial fan have been applied and modified to produce a hazard zonation map for the alluvial fan area by considering maximum expected discharge, local geometry of the channel and the possibility of channel occlusion and subsequent avulsion.     

The effects of geological heterogeneities and piezometric fluctuations on groundwater flow and chemistry in a hard-rock aquifer, southern India

Crystalline aquifers of semi-arid southern India represent a vital water resource for farming communities. A field study is described that characterizes the hydrodynamic functioning of intensively exploited crystalline aquifers at local scale based on detailed well monitoring during one hydrological year. The main results show large water-table fluctuations caused by monsoon recharge and pumping, high spatial variability in well discharges, and a decrease of well yields as the water table decreases. Groundwater chemistry is also spatially variable with the existence of aquifer compartments within which mixing occurs. The observed variability and compartmentalization is explained by geological heterogeneities which play a major role in controlling groundwater flow and connectivity in the aquifer. The position of the water table within the fracture network will determine the degree of connectivity between aquifer compartments and well discharge. The presented aquifer conceptual model suggests several consequences: (1) over-exploitation leads to a drop in well discharge, (2) intensive pumping may contribute to the hydraulic containment of contaminants, (3) groundwater quality is highly variable even at local scale, (4) geological discontinuities may be used to assist in the location of drinking-supply wells, (5) modeling should integrate threshold effects due to water-table fluctuations.     

The Taratash indenter and its role in the geological structure of the Urals

This work presents the results of studying zones bounded by the Archean and Early Proterozoic Taratash block, which breaks the meridional structure of the Urals, pinching its structural zones at the latitude of the town of Miass. The mesostructures of rupture zones, microtextures of tectonites, anisotropy of the magnetic susceptibility, and seismic-wave propagation rate in blastomylonites were studied. The kinematic history of the Taratash block consists of two phases: (1) exhumation in the Middle Riphean under conditions of crustal extension; and (2) the formation of an indenter in the Late Paleozoic under conditions of compression.     

Potential for deep geological sequestration of CO2 in Switzerland: a first appraisal

Possibilities to sequester anthropogenic CO₂ in deep geological formations are being investigated worldwide, but the potential within Switzerland has not yet been evaluated. This study presents a first-order appraisal based solely on geological criteria collated from the literature. The Swiss Molasse Basin (SMB) and the adjacent Folded Jura are the only realms of the country where CO₂ could conceivably be stored in saline aquifers. Evaluation of geological criteria at the basin-wide scale shows that the SMB–Jura has moderate potential (score of 0.6 on a scale from 0 to 1) when compared to basins elsewhere. At the intrabasinal scale, inspection of the stratigraphy reveals four regional candidate aquifers that are sealed by suitable caprocks: top Basement plus basal Mesozoic sandstones, all sealed by the Anhydrite Group; Upper Muschelkalk sealed by the Gipskeuper; Hauptrogenstein sealed by the Effinger Member, and Upper Malm plus Lower Cretaceous sealed by the Lower Freshwater Molasse. Nine geological criteria are defined to evaluate the storage potential of these and other smaller scale candidates. A numerical scoring and weighting scheme allows the criteria to be assessed simultaneously, permitting the storage potential to be depicted using the 0–1 scale in contoured maps. Approximately 5,000 km² of the central SMB exhibits potentials between 0.6 and 0.96. The Fribourg–Olten–Luzern area is the most favoured owing to the presence of several sealed aquifers within the preferred 800–2,500 m depth interval, and to its low seismicity, low geothermal gradient, low fault density, and long groundwater residence times. Smaller areas with good potential lie between Zürich and St. Gallen. In contrast, western Switzerland, the Jura and the southern SMB have markedly poorer potential. Considering only the portions of the aquifers with potential above 0.6, the theoretical, effective storage capacity of the basin is estimated to be 2,680 million tonnes of CO₂.     

中国地质灾害(以崩、滑、流为主)危险性分析与区划

论文提出了地质灾害（滑坡、崩塌、泥石流为主）危险性分析的步骤与方法。针对常规的地质灾害危险性分析评价模型，对致灾作用的各种影响因素采用主观赋予权重方法，将所有影响因子作为不变量看待而带来2个突出问题：由于权重确定的主观性，使危险性计算结果的可靠程度受到影响；危险性的过分确定性，与实际不相符。因此提出了利用层次分析方法确定权重，将主观判断工作由一个层次驱赶到下一个比较容易判断的层次上，一定程度上提高了权重取值的可靠性；另一方面，在详细分析了各种影响因素的基础上，突出了降雨的特殊作用。而且一改过去将降雨量作为参算因子的做法，采用临界降雨强度的超越概率参算，突出了其随机性，也提高了危险性计算的可靠程度。     

Cadomian terranes,wrench faulting and thrusting in the central Europe Variscides: geophysical and geological evidence

Sixty five per cent of the Paleozoic basement of western and central Europe is hidden by a sedimentary cover and/or sea. This work aims to remove that blanket to detect new structures which could used to build a more comprehensive model of the Variscan orogeny. It is based on the interpretation of various forms of data: (a) published gravity maps corrected for the effects of the crust-mantle boundary topography and light sedimentary basins; (b) aeromagnetic maps; (c) measurements of densities; and (d) induced and remanent magnetizations on rocks from Paleozoic outcrops of the upper Rhenish area. From the northern Bohemian Massif to the eastern Paris Basin, the Saxothuringian is characterized by a 500 km long belt of gravity highs, the most important being the Kraichgau high. Most of the corresponding heavy bodies are buried under a post-early Viséan cover. They are interpreted as relics of Late Proterozoic terranes overlain by an Early to Middle Paleozoic sequence, equivalent to the Bohemian terrane in the Bohemian Massif. The most probable continuation of these dense Bohemian terranes toward the west is the Southern Channel-Northern Brittany Cadomian terrane. The gravity lows are correlated with Variscan granites and pre- and early Variscan metagranites.Gravity and magnetic maps demonstrate large-scale displacement in Devonian-Early Carboniferous times along the parallel and equidistant, NW-SE striking, Vistula, Elbe, Bavarian, Bray and South Armorican dextral wrench faults. In the Vosges-Schwarzwald and Central Massif the faults continue with the east-west striking Lalaye-Lubine-Baden-Baden and Marche faults and with south vergent thrusts. The Bavarian faults shift the Kraichgau terrane by 150 km relative to the Bohemian terrane, whereas the offset of the Northern Brittany Cadomian relative to the Northern Vosges-Kraichgau terranes is estimated at 400 km along the Bray fault. Sinistral wrench faults are the NE-SW striking Sillon Houiller, Rheingraben, Rodl, Vitis and Diendorf faults. The southern Vosges-Schwarzwald Devonian-Dinantian basin is interpreted as a pull-apart basin at the south-easterly extremity of the Bray fault. The Bohemian and Kraichgau body form allochthonous terranes which were thrust over the Saxothuringian crust. Thrusting to the north-west was accompanied by back-thrusting and led to the formation of pop-up structures. Contemporaneous dextral and sinistral wrench faulting resulted in transpressive strain during collision. The zonal structure of the Variscides in the sense of Kossmat (1927) is relevant only to the Rhenohercynian Foreland Belt. Kossmat (1927) already spoke of a Moldanubian Region because it displays no real zonal structure. The Saxothuringian Zone was formed by terrane accretion. Their apparent zonal structure is not a pre-collisional feature, but only the result of accretion and collision.     

Enhanced groundwater vulnerability assessment in geological homogeneous areas: a case study from the Argentine Pampas

The southeast area of the Argentine Pampas is characterized by the presence of an unconfined aquifer in a wide plain. A methodology is proposed that deals with the aquifer vulnerability where the homogeneity of the hydrogeological variables used by traditional methods (in this case, DRASTIC-P) causes vulnerability maps to show more than 80% of the territory under the same class. This absence of discrimination renders vulnerability maps of little use to decision-makers. In addition, the proposed methodology avoids the traditional vague classification (high, low, and moderate vulnerability) which is highly dependent on subjectivity in its association of each class with hydrogeological considerations. That traditional vulnerability assessment methodology was adapted using a geographic information system to reclassify classes, based on the Natural Breaks (Jenks) method. The pixel-to-pixel comparison between the result obtained by the DRASTIC-P and the reclassified classes generates the so-called operational vulnerability index (OVI), which shows four classes, associating each with different hydrogeological requirements to make decisions.     

Failure and flow development of a collapse induced complex landslide: the 2005 Kuzulu (Koyulhisar, Turkey) landslide hazard

Koyulhisar located in a slope of hilly region and constructed in the side of a mountain along the North Anatolian Fault Zone is frequently subject to landslides. A catastrophic landslide occurred on the morning of 17 March 2005 in the North of the Kuzulu district of Koyulhisar (Sivas, Turkey). This landslide caused widespread loss of life, and damage to buildings, and lifelines. Fifteen people were dead and five were injured, 21 houses and a minaret were covered and damaged severely. The case study presented in this paper describes and analyses the results of the detailed surveys of an interesting landslide in Kuzulu district of Koyulhisar (Sivas, Turkey), based on field and laboratory measurements and monitoring of the slide area. Landslide initiated as a collapse, and developed into debris avalanches in the valley. This phenomenon caused a disaster in the Kuzulu district. The importance of this landslide in particular has been recognized both in terms of its consequence for the people and structures and in terms of its role in allowing an understanding of process and properties of landslide triggered by a collapse in limestone karst. In view of the potential for such events to occur again in this area and environs, understanding of the failure mechanism is very crucial.     

Contribution of geophysical surveys to groundwater modelling of a porous aquifer in semiarid Niger: An overview

Subsurface geophysical surveys were carried out using a large range of methods in an unconfined sandstone aquifer in semiarid south-western Niger for improving both the conceptual model of water flow through the unsaturated zone and the parameterization of numerical a groundwater model of the aquifer. Methods included: electromagnetic mapping, electrical resistivity tomography (ERT), resistivity logging, time domain electromagnetic sounding (TDEM), and magnetic resonance sounding (MRS). Analyses of electrical conductivities, complemented by geochemical measurements, allowed us to identify preferential pathways for infiltration and drainage beneath gullies and alluvial fans. The mean water content estimated by MRS (13%) was used for computing the regional groundwater recharge from long-term change in the water table. The ranges in permeability and water content obtained with MRS allowed a reduction of the degree of freedom of aquifer parameters used in groundwater modelling.     

Double-parameter threshold and its formation mechanism of the colluvial landslide: Xintan landslide, China

Data compiled from monitoring the displacement resulting from the Xintan landslide in China was analyzed. The stability of the demonstrated colluvial slope has a close correlation with two parameters, the velocity of the displacement and the angle of the surface vector. The stability trend can be described and evaluated by both the velocity of the displacement and the vector angles. The displacement vector angle, for which there is no substitute, serves as an explicit criterion for the stability of the slope, hence it is significant in the prediction of the catastrophic movement of landslides. A systematic analysis of the features of the vector angles of the surface displacement space and time was performed. The evolving mechanism of space-time and the characteristics of the displacement vector angles were deduced. On the basis of these deductions and by using principles of statistics, the double-parameter threshold for forecasting the stability of the colluvial slopes was established. According to the double-parameter threshold, a calculation and evaluation of stability was completed in terms of the monitoring data of the F-series of points on the Xintan slope. The forecast results coincided with the destabilized timetable, thus demonstrating that the double-parameter criterion has, to a certain extent, precision and practical application for forecasting of landslides.     

An integrative geological and geophysical approach to characterize a superficial deltaic aquifer in the Camargue plain,France

Deltaic aquifers are complex due to the important heterogeneity of their structure and their hydrogeological functioning. Auger drilling provides localized, but very robust geological and hydrogeological information, while geophysical surveys can provide integrated subsurface information. An effective, easy-to-use and low-cost methodology combining geological/hydrogeological information from Auger drillings and the results from three geophysical techniques (Electromagnetic mapping, Electrical Sounding and Electrical Resistivity Tomography) is being developed to characterize the structure of a typical Mediterranean deltaic aquifer. A first hypothesis about hydrodynamic properties of the aquifer is also obtained. The study area is located in the Rhone delta (Middle Camargue/southern France). Integration of geophysical and geological techniques allowed identifying the presence and lateral extension of the Saint-Ferréol paleochannel, the vertical contact between lagoonal–fluvial deposits and the marine clayed silt that separate the superficial aquifer from the deeper aquifer. Likewise, high north–south heterogeneity and east–west homogeneity were highlighted in the study area. Presence of clay in sandy deposits in the low areas implies changes in lateral hydraulic permeability. This fact, jointed to the low hydraulic gradient, suggests a slow groundwater flow in the local system. The Rhone delta presents a typical configuration of a Mediterranean deltaic aquifer, thus this methodological approach can be used for similar deltaic Mediterranean systems.     

Hydrochemical appraisal of groundwater and its suitability in the intensive agricultural area of Muzaffarnagar district,Uttar Pradesh,India

Muzaffarnagar is an economically rich district situated in the most fertile plains of two great rivers Ganga and Yamuna in the Indo-gangetic plains, with agricultural land irrigated by both surface water as well as groundwater. An investigation has been carried out to understand the hydrochemistry of the groundwater and its suitability for irrigation uses. Groundwater in the study area is neutral to moderately alkaline in nature. Chemistry of groundwater suggests that alkaline earths (Ca + Mg) significantly exceed the alkalis (Na + K) and weak acids exceed the strong acids (Cl + SO₄), suggesting the dominance of carbonate weathering followed by silicate weathering. Majority of the groundwater samples (62%) posses Ca–Mg–HCO₃ type of hydrochemical species, followed by Ca–Na–Mg–HCO₃, Na–Ca–Mg–HCO₃, Ca–Mg–Na–HCO₃–Cl and Na–Ca–HCO₃–SO₄ types. A positive high correlation (r ² = 0.928) between Na and Cl suggests that the salinity of groundwater is due to intermixing of two or more groundwater bodies with different hydrochemical compositions. Barring a few locations, most of the groundwater samples are suitable for irrigation uses. Chemical fertilizers, sugar factories and anthropogenic activities are contributing to the sulphate and chloride concentrations in the groundwater of the study area. Overexploitation of aquifers induced multi componential mixing of groundwater with agricultural return flow waters is responsible for generating groundwater of various compositions in its lateral extent.