共查询到20条相似文献，搜索用时 15 毫秒
1.
The study area Hindon -Yamuna interfluve region is underlain by a thick pile of unconsolidated Quaternary alluvial deposits and host multiple aquifer system. Excessive pumping in the last few decades, mainly for irrigation, has resulted in a significant depletion of the aquifer. Therefore, proper groundwater management of Hindon-Yamuna interfluve region is necessary. For effective groundwater management of a basin it is essential that careful zone budget study should be carried out. Keeping this in view, groundwater flow modelling was attempted to simulate the behavior of flow system and evaluate zone budget. Visual MODFLOW, pro 4.1 is used in this study to simulate groundwater flow. The model simulates groundwater flow over an area of about 1345 km2 with a uniform grid size of 1000 m by 1000 m and contains three layers, 58 rows and 37 columns. The horizontal flows, seepage losses from unlined canals, recharge from rainfall and irrigation return flows were applied using different boundary packages available in Visual MODFLOW, pro 4.1. The river — aquifer interaction was simulated using the river boundary package. Simulated pumping rates of 500 m3/day, 1000 m3/day and 1500 m3/day were used in the pumping well package.The zone budget for the steady state condition of study area indicated that the total annual direct recharge is 416.10 MCM and the total annual groundwater draft through pumping is of the order of 416.63 MCM. Two scenarios were considered to predict aquifer system response under different conditions. Sensitivity analysis on model parameters was conducted to quantitatively evaluate the impact of varying model inputs. Based on the results obtained from the sensitivity analysis, it was found that the model is more sensitive to hydraulic conductivity and recharge parameter. Present study deals with importance of groundwater modelling for planning, design, implementation and management of groundwater resources. 相似文献
2.
Thomas Foulon Ali Saeidi Romain Chesnaux Miroslav Nastev Alain Rouleau 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2018,12(1):74-86
The spatial distribution of soil shear-wave velocity and the fundamental period of vibration were selected as input parameters for the determination of potential seismic site effects in the Saguenay region, Canada. The methodology used in this study involved three clear steps. First, a 3D geological model of the surficial deposits was built taking into consideration the type, spatial distribution and thickness of the deposits. Second, representative average Vs values were determined for each of the major soil units. Finally, the average shear-wave velocity from the ground surface to bedrock (Vsav), the shear-wave velocity of the upper 30 m (Vs30) and the fundamental site resonance period (T0) were calculated over a regular grid for the study area. The results include the spatial distribution of the fundamental site resonance period, the average shear-wave velocity in the first 30 m of the ground and the spatial distribution of National Building Code of Canada seismic soil classes for the Saguenay region. 相似文献
3.
Processes of late Quaternary turbidity current flow and deposition on the Var deep-sea fan, north-west Mediterranean Sea 总被引：3，自引：1，他引：3
High-resolution seismic boomer profiles, with a vertical resolution of less than 1 m, together with piston cores and previous side-scan sonar data, are used to describe late Quaternary sedimentation on the Var deep-sea fan. Chronological control is provided by foram biostratigraphy and radiocarbon dating in cores, and is extended over the fan by seismic correlation. Regional erosional events correspond to the oxygen isotopic stage 2 and 6 glacial maxima. Cores and seismic data define a widespread surface sand layer that is correlated with prodelta failure in 1979 and subsequent submarine cable breaks. Numerical modelling constrains the character of this 1979 turbidity current. It originated from a relatively small slide on the upper prodelta that put sufficient material in suspension to form an accelerating turbidity current which eroded sand from the Var Canyon. The turbidity current was only 30 m thick on the Upper Valley, but experienced significant flow expansion in the Middle Valley to thicknesses of more than 120 m, where it spilled over the eastern Var Sedimentary Ridge at a velocity of about 2·5 m s?1. Other Holocene turbidity currents (with a recurrence interval of 1000 years) were somewhat muddier and thicker, but also deposited sand on the levees of the Middle Valley, and are inferred to have had a similar slide-related origin. Late Pleistocene turbidity currents deposited thick mud beds on the Var Sedimentary Ridge. The presence of sediment waves and the mean cross-flow slope inferred from levee asymmetry indicates that some of these flows were many hundreds of metres thick and flowed at velocities of about 0·35 m s?1. This contrast with Holocene turbidites suggests that a slide origin is unlikely. Estimated times for deposition of thick mud beds on the levees are many days to weeks. The Late Pleistocene flows may therefore result from hyperpycnal flow of glacial outwash in the Var River. The variation in the Late Pleistocene to Holocene turbidite sedimentation is controlled more by variations in sediment supply than by sea-level change. 相似文献
4.
Orientation studies were carried out by the BRGM mission in Saudi Arabia between 1982–1986 to investigate the dispersion of gold in soils and wadi sediments and to define the optimum sample medium around eight prospects in the central Arabian pediplain. A comparison of gold distribution in several sieved fractions with various pedologic horizons shows that the distribution of gold changes abruptly from the coarser sizes near the source to the finest sizes 150 m downstream.The coarse fraction recommended by previous workers is not representative and yields erratic results in the specific environment of the pediplain. Gold is enriched and more homogeneously distributed in the minus 80 μm fraction of the skeletal soils and wadi sediments.Regional geochemical survey can be effective using a sensitive analytical method for gold and the minus 80 μm fraction of the brown gravelly sediment with a minimum density of 2 samples per km2. Geochemical halos in the 30–50 ppb range indicate gold mineralization 500 to 1000 m upstream, depending on relief.In a first follow-up stage, continued use of the same size of the upper argillaceous layer with a regular reg sampling grid gives more contrasted and more extensive anomalies than using a coarse material. These anomalies may be slightly offset by the present arid erosion. A second follow-up stage is then recommended at a closer grid and sampling the brown blocky layer below the surficial reg pavement. Again, the use of the finest fraction at this exploration stage has given the best probability of finding a blind gold target.Optical determination of gold on a nonmagnetic fraction of heavy panconcentrate is not recommended, because nugget growth is practically absent in the present arid conditions and flour-sized gold particles are lost in desliming samples. 相似文献
5.
Flow parameters (velocity and density) for turbidity currents in the Northwest Atlantic Mid-Ocean Channel (NAMOC) have been determined based on two different approaches, channel geometry and grain-size distributions of turbidites. Channel geometry has been obtained by a quantitative morphological analysis of the NAMOC which shows three genetically different segments in the upper 2000 km: (1) an upper 350 km-long ‘equilibrium channel’, (2) a middle 700 km-long ‘modified equilibrium channel’and (3) a lower ‘basement-controlled channel’which is more than 1000 km-long. In contrast to other meandering submarine channels the NAMOC has very low sinuosities and gradients. A consistently higher right-hand levee limits mean flow velocities to 3ms?1 and channel geometry indicates mean flow velocities of 0·86 m s?1 that decrease within the equilibrium channel to 0·05 m s?1. Grain-size distributions on the levees and in the channel suggest strong vertical velocity and density gradients for bank-full flows with velocities of up to 8 m s?1 and excess densities up to 87 kg m?3 at the base, and 0·45 m s?1 and 4 kg m?3 at the top. The internal shear produced by these strong vertical gradients results in a decoupling of the current head and body. Channel geometry appears to be mainly the result of the slowly moving dilute body of the current. 相似文献
6.
F. W. L. Kho B.Sc. M.Eng. P. L. Law M.Sc. Sc.D. S. H. Lai B.Eng. M.Sc. Ph.D. Y. W. Oon B.Eng. M.Eng. L. H. Ngu B.Eng. M.Eng. H. S. Ting B.Eng. 《International Journal of Environmental Science and Technology》2009,6(2):203-210
Mathematical simulations on dam break or failure using BOSS DAMBRK hydrodynamic flood routing dam break model were carried out to determine the extent of flooding downstream, flood travel times, flood water velocities and impacts on downstream affected residences, properties and environmental sensitive areas due to floodwaters released by failure of the dam structure. Computer simulations for one of the worse case scenarios on dam failure using BOSS DAMBRK software accounted for dam failure, storage effects, floodplains, over bank flow and flood wave attenuation. The simulated results reviewed a maximum flow velocity of 2.40 m/s with a discharge of approximately 242 mз /s occurred at 1.00 km downstream. The maximum discharge increased from 244 m3/s (flow velocity = 1.74 m/s occurred at 8th. km) to 263 m3/s (flow velocity = 1.37 m/s occurred at 12th. km); about a 39% drop in flow velocity over a distance of 4.00 km downstream. If the entire dam gives way instantly, some spots stretching from 0.00 km (at dam site) to approximately 3.40 km downstream of the dam may be categorized as “danger zone”, while downstream hazard and economic loss beyond 3.40 km downstream can be classified as “low” or “minimal” zones. 相似文献
7.
J. William Miller Jr. 《Mathematical Geology》1991,23(2):201-218
A computer simulation method has been developed to find efficient drilling grids for mineral deposits. A well-known ore deposit is used as a model to develop an efficient pattern for undiscovered ore bodies in the same area or in other prospects where similar geometry is suspected. The model for this study is the Austinville, Virginia deposit, a Mississippi Valley-type deposit composed of 17 ore bodies totaling 34 million short tons (30 million metric tons). The method employs a computer program that simulates drilling the model deposit with different patterns, including various levels of follow-up drilling. Follow-up holes are drilled in fences at one half the original spacing around holes in the grid that show ore-grade mineralization. Each pattern is drilled 100 times from random starting locations to provide a range of outcomes of drilling, including the best, worst, and most likely. For this study, patterns of 100 drill holes were composed of 10 fences spaced 1000–5000 feet (305–1524 m) apart, each with 10 holes spaced 200–1000 feet (61–305 m) apart. In all, 25 grids were used with zero to three levels of follow-up drilling. The 600/2000 grid, with drill holes spaced 600 feet (183 m) apart in fences spaced 2000 feet (610 m) apart, was compared with the 200/5000 grid because they represented contrasting outcomes. The 600/2000 grid penetrated many ore bodies consistently but with few multiple hits to individual ore bodies; whereas the 200/5000 grid inconsistently penetrated few ore bodies with many multiple hits. The 600/2000 grid was more efficient than the 200/5000 grid at hitting large ore bodies of 1,000,000 short tons or greater (900,000 metric tons or greater) and was made more effective by adding one cycle of follow-up drilling. The 600/2000 grid had a 97% chance of hitting one or more large ore bodies with at least one drill hole per ore body, and the 200/5000 grid had a 64% chance. Once hit, there was an 82% chance that the largest ore body would be penetrated by three or more holes when using the 600/2000 grid and an 88% chance using the 200/5000 grid. 相似文献
8.
长江中下游金属矿集区近地表速度结构层析成像实验及应用 总被引：1，自引：0，他引：1
利用矿集区获得的小道距、长排列接收的地震反射初至波走时数据,运用层析成像方法,首次得到长江中下游典型金属矿集区——庐枞火山岩盆地近地表1000m以上的交叉速度结构。各剖面精细的速度结构揭露出庐枞矿集区隐伏的正长岩体顶界面深度与起伏形态,发现岩体顶面凸起及陡变化部位与矿体分布存在着明显的对应关系,罗河铁矿、小岭铁矿、龙桥铁矿、马鞭山铁矿处对应着高速层顶界面的凸起位置。罗河断裂在lz06-1线与lz06-3线表现为明显的横向速度变化界面。这些结果表明,长排列的深地震反射初至波走时层析成像方法能够为金属矿集区深部隐伏矿床的勘探研究提供丰富的地壳浅表结构(0～1000m)信息。 相似文献
9.
During 1976 the first installment of a long range seismic profile was conducted in the North Pacific to a range of 600 km using shots to two tons in size. The line was shot to a closely-spaced array of Scripps ocean bottom seismographs and was parallel to magnetic anomaly 32 at an age of approximately 70 · 106 yr. The line extended between the Clarion and Molokai Fracture Zones and did not cross any major topographic features. Linearized and extremal travel-time inversions were conducted to provide bounds on the compressional velocity as a function of depth. The velocity does not exceed 8.4 km s−1 to a depth of 60 km at which point the data no longer provide any resolution. The constraints on the acceptable models were improved by using array processing methods to measure phase velocity and synthetic seismogram techniques to model phase and amplitude information. The oceanic crust is composed of a series of gradients with no first order discontinuities. The “Moho” is smeared out over a depth of 1.5–2.0 km even though “wide-angle reflections” from the Moho, the phase PMP, are clearly seen in the data. The upper lithosphere is characterized by a general tendency for the velocity to decrease with depth and the tendency is occasionally overwhelmed (at about 27 and 52 km depth) by rapid velocity changes perhaps associated with phase or compositional changes. 相似文献
10.
F. Chevalier M. Guiraud J.-P. Garcia J.-L. Dommergues D. Quesne P. Allemand T. Dumont 《地学学报》2003,15(6):410-416
Displacement rates of normal faults deduced from stratigraphic data are often unreliable. Here we calculate the velocity of motion on a normal fault from the variations in accommodation potential on both sides of the fault within a high‐resolution time‐frame established by biostratigraphy and physical stratigraphy. Our example is the Ornon normal fault bounding the Early Jurassic Bourg‐d'Oisans Basin formed during Tethyan rifting. We show that motion on the fault was discontinuous when examined at high resolution and over a long time interval. During a first interval (Hettangian to Sinemurian Arietites bucklandi zone) a low rate of displacement (=202–423 m Myr?1) coeval with diffused extensional deformation throughout the sedimentary basin is observed. A second interval of localized deformation (Early Sinemurian Caenisites turneri zone) is characterized by higher rates of displacement on the fault (1846 m Myr?1). Our results concur with recent numerical models identifying the main stages of extensional deformation. 相似文献
11.
Radiocarbon analyses were carried out in the annual bands of a 40 year old coral collected from the Gulf of Kutch (22.6°N,
70°E) in the northern Arabian Sea and in the annual rings of a teak tree from Thane (19°14′N, 73°24′E) near Bombay. These
measurements were made in order to obtain the rates of air-sea exchange of CO2 and the advective mixing of water in the Gulf of Kutch. The Δ14C peak in the Thane tree occurs in the year 1964, with a value of ∼630‰, significantly lower than that of the mean atmospheric
Δ14C of the northern hemisphere (∼ 1000‰). The radiocarbon time series of the coral was modelled considering the supply of carbon
and radiocarbon to the gulf through air-sea exchange and advective water transport from the open Arabian Sea. A reasonable
fit for the coral data was obtained with an air-sea CO2 exchange rate of 11–12 mol m−2 yr−1, and an advective velocity of 28 m yr−1 between the Arabian Sea and the Gulf of Kutch; this was based on a model generated time series for radiocarbon in the Arabian
Sea. The deduced velocity (∼ 28 m yr−1) of the advective transport of water between the gulf and the Arabian Sea is much lower than the surface tidal current velocity
in this region, but can be understood in terms of net fluxes of carbon and radiocarbon to the gulf to match the observed coral
Δ14C time series. 相似文献
12.
Hurricane Frances is shown to greatly alter the hydrodynamics within Tampa Bay, Florida, and the exchange of water with the
Gulf of Mexico in both observational data and a realistic numerical circulation model of the Tampa Bay estuary. Hurricane
Frances hit Tampa Bay on September 5, 2004 with surface winds peaking twice near 22 m s−1. There were three stages to the hydrodynamic effect of Frances on Tampa Bay. The first stage included the approach of Frances
up to the first wind peak. The winds were to the south and southeast. During this stage sea level was maintained below mean
sea level (MSL) and the residual current (demeaned, detided) was weak. The second stage began as the winds turned to the east
and northeast, as the eye passed near the bay, and ended as the second wind peak appeared. During this stage the residual
currents were strongly positive (into the bay), raising sea level to 1.2 m above MSL at St. Petersburg. The measured residual
circulation peaked at over +0.7 m s−1 near the surface. The model shows this velocity peak yielded a maximum volume flux into the bay of +44,227 m3 s−1, displacing a total volume of 1.5 billion m3 in just a few hours, about 42% of the bay volume. In the third stage a strong negative flow developed as the wind and sea
level relaxed to near normal levels. The ADCP measured a peak outflow of −0.8 m s−1 during this time. Model results indicate a maximum flux of −37,575 m3 s−1, and that it took about 50 h to drain the extra volume driven into the bay by Hurricane Frances. 相似文献
13.
About 30 samples representing major lithologies of Sulu ultrahigh-pressure (UHP) metamorphic rocks were collected from surface exposures and exploration wells, and compressional (Vp) and shear wave (Vs) velocities and their directional dependence (anisotropy) were determined over a range of constant confining pressures up to 600 MPa and temperatures ranging from 20 to 600 °C. Samples range in composition from acidic to ultramafic. P- and S-wave velocities measured at 600 MPa vary from 5.08 to 8.64 km/s and 2.34 to 4.93 km/s, respectively. Densities are in the range from 2.60 to 3.68 g/cm3. To make a direct tie between seismic measurements (refraction and reflection) and subsurface lithologies, the experimental velocity data (corresponding to shallow depths) were used to calculate velocity profiles for the different lithologies and profiles of reflection coefficients at possible lithologic interfaces across the projected 5000-m Chinese Continental Scientific Drilling Program (CCSD) crustal segment. Comparison of calculated in situ velocities with respective intrinsic velocities suggests that the in situ velocities at shallow depths are lowered by an increased abundance of open microcracks. The strongly reflective zone beneath the Donghai drill site can be explained by the impedance contrasts between the different lithologies. Contacts between eclogite/peridotite and felsic rocks (gt-gneiss, granitic gneiss), in particular, may give rise to strong seismic reflections. In addition, shear-induced (lattice preferred orientation (LPO)-related) seismic anisotropy can increase reflectivity. For the explanation of the high velocity bodies (>6.4 km/s) around 1000 m and below 3200-m depth, large proportions of eclogite/peridotite (about 40 and 30 vol.%, respectively) are needed. 相似文献
14.
为模拟淹没丁坝群平面二维水流运动,提出了淹没丁坝群二维水流数值模拟新方法并建立了数学模型。新方法的主要实施方案:① 将丁坝视为无厚度坝,用网格线概化丁坝;② 采用新的网格节点布置形式,即水深、流速节点布置于网格界面上,水位节点布置于网格中心,有别于一般交错网格节点布置。模型采用基于结构网格下的有限体积法对方程组进行离散,同时将淹没丁坝坝顶水深代入离散方程中进行求解。采用已有的水槽试验资料,进行了初步验证,模拟了长江下游东流水道已建丁坝群工程实施后河道的流场和水位场,结果表明计算和实测符合较好。 相似文献
15.
TOPMODEL是目前被广泛应用的半分布式流域水文模型,它以地形为基础的特点使得DEM的空间分辨率成为影响模型模拟结果准确性的重要参数。不同分辨率的DEM将计算出不同的地形指数ln(α/tanβ)分布,其作为TOPMODEL的地形参数直接影响着模型的模拟结果。以10 m分辨率的DEM为原始数据,生成10~1 000 m等17种分辨率的DEM,使用地形信息熵的概念,比较不同分辨率的DEM对地形信息提取的影响。假设TOPMODEL在10 m分辨率的DEM计算的流量过程线为观测值,对比了不同分辨率的DEM对流量过程线和Nash效率系数产生的变化。对于所研究的流域,150 m分辨率是建立TOPMODEL模型的最佳值,300 m分辨率是保证模型结果有效的基本要求。使用Monte Carlo方法计算TOPMODEL中参数对DEM分辨率的敏感性,指出在模型的5个参数中,只有饱和导水系数T0对DEM分辨率敏感。 相似文献
16.
The release of a digital elevation model (DEM) for Australia on a 9″ (～250 m) grid has enabled the computation of gravimetric terrain corrections thus allowing the computation of complete Bouguer anomalies across the continent. The terrain correction was calculated through a two‐dimensional fast Fourier transform algorithm applied to a linear, planar approximation of the terrain‐correction formula, and with a constant topographic density of 2670 kg.m‐3. The technique was applied to two datasets in order to test for instabilities in the terrain‐correction algorithm: the original 9″ DEM, and a 27″ DEM averaged from the 9″ data. The 27″ terrain corrections were compared with values supplied by the Australian Geological Survey Organisation in Tasmania: 86% of these data were found to agree within 3.91 μm.s‐2; 98% agreed to within 5.32 μm.s‐2 (1σ). 相似文献
17.
庐枞铁多金属矿集区龙桥铁矿反射地震初至波层析成像与隐伏矿床预测 总被引：5，自引：3，他引：2
为落实安徽庐枞地区北部的龙桥铁矿含矿层位在第二找矿深度的空间分布,本文应用小道距、长排列接收的地震反射初至波走时数据,运用层析成像方法,得到该地区近地表1000m以上的速度结构。研究结果显示,反射地震初至波携带了丰富的上地壳速度结构特征和界面变化的构造信息,精细的速度结构揭露出龙桥铁矿隐伏岩体顶界面深度与起伏形态,发现岩体顶面凸起及陡变化部位与矿体分布存在着明显的对应关系。长排列的深地震反射初至波走时层析成像方法能够为金属矿集区深部隐伏矿床的勘探与研究提供岩体的空间分布信息。 相似文献
18.
B. A. Kazanskii 《Geotectonics》2006,40(2):150-159
Diagrams of the various distributions of the potential energy of the continental and oceanic-bottom topography as a quantitative indices of energy consumption by tectonic processes have been calculated and plotted for the first time on the basis of high-resolution ETOPO 2′ digital data on a 2′ × 2 ′ uniform network with height intervals of 100 m. The potential energy of the continents and oceanic bottom is mainly stored in mountainous regions of Asia and South America with an anomalous type of energy distribution and in mid-oceanic ridges, respectively. The topography of the oceanic bottom bears five times more energy than the continental topography. With allowance for the isostatic compensation of denudation, the bulk reserve of the potential energy of the global topography is estimated at 1033 erg, a value which amounts to only an insignificant fraction of other items in the energetic budget of the Earth. Fifty percent of this energy has been gained over the last 70 Ma. Currently, the rate of accumulation of the potential energy of the topography is 1025 erg/yr, i.e., 1000 times less than the bulk geothermal flow and 10 times less than energy released by all earthquakes during a year. So far, there are no grounds to bind the potential energy of the Earth’s topography with a specific source. 相似文献
19.
David T Heggie 《Geochimica et cosmochimica acta》1982,46(7):1301-1306
Copper concentrations have been measured in surface <75 m waters of the central Bering Sea. Concentrations of 2–4 nmole kg?1 were measured in the Zhemchung Canyon region where water depths are greater than 1000 m. Concentrations are higher 2–25 nmole kg?1 on the shallow <100 m continental shelf, inshore of a hydrographic front at the 100 m isobath. Copper-depth profiles on the continental shelf water mass are dominated by Cu concentrations increasing toward the sediments. These trends may be maintained by a flux of Cu from surficial sediments. A frontal system over the 100 m isobath acts to control the flux of Cu, a significant part of which apparently emanates from the sediments, between the continental shelf and the central Bering Sea basin. The benthic shelf Cu flux was constrained to be less than 3 nmole cm?2 yr?1. 相似文献
20.
R.D. Hyndman 《Tectonophysics》1979,59(1-4)
Laboratory samples from the upper oceanic crust (tholeiitic basalt flows) that have not been significantly weathered, hydrothermally altered or fractured have a typical Poisson's ratio of 0.30 (
) and a compressional velocity of 6.0 km s−1; from the middle crust (dolerite sheeted dykes) a ratio of 0.28 (
) and a velocity of 6.7 km s−1; from the lower crust (gabbro) a ratio of 0.31 (
) and a velocity of 7.1 km s−1; and from the uppermost mantle a ratio of 0.24 (
) and a velocity of 8.4 km s−1. These sample values are representative of the large scale insitu values for the middle and lower crust and for the upper mantle. The upper crust is modified by several processes that decrease the velocity and generally increase Poisson's ratio: (1) the formation of an irregular layer of low temperature weathering generally less than 50 m thick; (2) large scale porosity in the form of drained pillows and lava tubes, of talus and rubble and of large open fractures; (3) where there was a high sedimentation rate over the ridge that formed the crust, hydrothermal alteration and intercalation of basalt and sediments. The Poisson's ratios of both high velocity sediments and of crystalline continental crustal rocks generally are significantly lower than the ratios of oceanic crustal rocks of similar compressional wave velocity. Thus, the use of shear wave velocities should permit the separation of these different formations which frequently cannot be distinguished on the basis of compressional wave seismic refraction data alone. 相似文献