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1.
为了选择合理的南海南部海底沉积物的声速反演模型,分别利用Wood方程、Buckingham模型、Biot-Stoll模型等声波传播理论模型计算了沉积物的纵波声速,结合沉积物实测声速和物理参数等,对比了模型计算声速与实测声速的变化特征。声速实测值与模型计算值的对比表明,Buckingham模型计算值与实测值的平均偏差最小。研究区实测声速比和模型计算声速比的分布表明,声速的变化特征与沉积环境具有相关性,声速模型计算值与实测值具有相似的变化特征;模型计算声速与实测声速的垂向变化规律不相同,模型计算声速随深度基本不变,而实测声速在陆架、陆坡和海槽等沉积环境中呈现出多种垂向分布特征。研究结果认为,侧重于沉积物孔隙性的Biot-Stoll理论仅适用于陆架区粗颗粒沉积物,兼具流体和弹性固体双重性质的Buckingham理论具有更广的适用范围。该研究对获取南海南部海域沉积物声速分布特征有重要意义,可为多波束测深或浅地层精细解释等提供基础资料。 相似文献
2.
Field measurement and numerical modelling of aeolian mass flux distributions on a sandy beach 总被引：6，自引：0，他引：6
Steven L. Namikas 《Sedimentology》2003,50(2):303-326
ABSTRACT The vertical and horizontal distributions of aeolian mass flux were measured at Oceano Dunes, California, and these data were used to evaluate a numerical model of saltation. Grain‐size analyses showed that the distributions of the modal sediment size class corresponded closely to those of the total sediment population, and modelling thus focused on replicating the distributions of the mean grain size. Although much previous work has assumed that the mean launch speed of saltating particles varies in proportion to shear velocity, simulations using a constant mean launch speed were found to yield the closest approximations to the mass flux distributions observed in the field. Both exponential and gamma distributions of launch velocity produced realistic simulations, although the latter approach required the inclusion of an additional reptation component to achieve good results. A range of mean launch angles and an equivalent sphere correction were also found to generate comparable results, providing the other input parameters could be varied freely. All the modelling approaches overestimated the proportion of mass flux occurring at the bottom of the vertical distributions, and underestimated the proportion occurring at the upwind end of the horizontal distributions. No theoretical shortcoming that would account for these small, but systematic, discrepancies could be identified, and experimental error thus represents a more plausible explanation. The conclusion that mean grain launch speeds are essentially constant and independent of shear velocity suggests that the additional kinetic energy extracted by grains under more energetic wind conditions is largely transferred to the bed, and that increases in the transport rate are therefore driven primarily by the ejection of additional grains. It is suggested that the kinetic energy of rebounding grains is constrained by the ability of the bed to resist deformation, equivalent to a plastic limit. Hence, grains of larger mass (diameter) rebound from the bed at lower speeds, and follow shorter, lower trajectories, as has been widely observed previously. 相似文献
3.
通过模型实验,探讨了松散土坡3种不同结构特征条件下(均匀坡体(坡体物料均匀混合)、平行坡体(土层成层且层面与滑面平行)和斜交坡体(土层成层且层面与滑面斜交))形成滑坡堰塞体的动力过程和堆积特征,通过分区域取样及三维扫描技术研究了堰塞体的物质分布规律与形态特征。研究结果表明:堰塞体堆积特征与坡体特征存在紧密联系,堰塞体纵向(沿主沟道方向)和横向(沿滑坡运动方向)上的物质分布与坡体纵向和横向的物质分布特征基本对应;在垂向(表层到底部)上,由于不同坡体条件下滑坡的动力过程和机理不同,从而导致堰塞体堆积特征存在一定区别。均匀坡体和平行坡体呈整体启动模式,运动过程中物料间存在垂向渗透和交换作用,导致堰塞体物质在垂向上呈明显的上粗下细反粒序分布特征,堰塞体横剖面多呈平坦型和倾斜型。斜交坡体呈分层启动模式,运动堆积过程中保持原有层序,粗、细颗粒先后启动条件下颗粒间存在推挤、爬升和水平渗透作用,使得堰塞体更加密实且垂向上也呈现反粒序分布特征,横剖面多呈起伏型。本研究为滑坡堰塞体稳定性快速评估和复原滑坡初始状态提供依据。 相似文献
4.
The importance of relict burrow structures and burrow irrigation in controlling sedimentary solute distributions 总被引：1，自引：0，他引：1
Robert C. Aller 《Geochimica et cosmochimica acta》1984,48(10):1929-1934
Some areas of the seafloor, particularly the deep sea, are characterized by large numbers of apparently uninhabited or relict burrow structures formed by macrobenthic organisms. Because of low sedimentation rates or lack of physical disturbance these structures are stable for long periods of time and could potentially influence solute diffusion patterns in surface sediments. A two-dimensional diffusionreaction model which allows for diffusive rather than advective transport within stagnant, water-filled burrows demonstrates that, in the absence of advective irrigation, relict burrow structures are unlikely in most cases to significantly alter average solute distributions from those predicted by one-dimensional vertical models. This conclusion assumes changes in diffusive transport properties alone and does not account for any effects of relict structures on reaction rates or physical ventilation of deposits by bottom currents. Significant changes (≥5%) in solute distributions are generally produced only when the ratio of the halfdistance between burrows to relict burrow radii is ≤10 and sedimentary diffusion coefficients are ≤60% that in free solution. Because solute distributions in stagnant burrow waters are nearly that in surrounding sediment, sediment-water solute fluxes are also essentially unaffected by relict burrows except at extremely high abundances or fairly large differential diffusion rates between sediment and free solution. In contrast, even at low abundance, biologically irrigated or physically ventilated burrows produce major changes in solute transport and build-up patterns. 相似文献
5.
Coastal communities in the western United States face risks of inundation by distant tsunamis that propagate across the Pacific Ocean as well as local tsunamis produced by great (Mw?>?8) earthquakes on the Cascadia subduction zone. In 1964, the Mw 9.2 Alaska earthquake launched a Pacific-wide tsunami that flooded Cannon Beach, a small community (population 1640) in northwestern Oregon, causing over $230,000 in damages. However, since the giant 2004 Indian Ocean tsunami, the 2010 Chile tsunami and the recent 2011 Tohoku-Oki tsunami, renewed concern over potential impacts of a Cascadia tsunami on the western US has motivated closer examination of the local hazard. This study applies a simple sediment transport model to reconstruct the flow speed of the most recent Cascadia tsunami that flooded the region in 1700 using the thickness and grain size of sand layers deposited by the waves. Sedimentary properties of sand from the 1700 tsunami deposit provide model inputs. The sediment transport model calculates tsunami flow speed from the shear velocity required to suspend the quantity and grain size distribution of the observed sand layers. The model assumes a steady, spatially uniform tsunami flow and that sand settles out of suspension forming a deposit when the flow velocity decreases to zero. Using flow depths constrained by numerical tsunami simulations for Cannon Beach, the sediment transport model calculated flow speeds of 6.5?C7.6?m/s for sites within 0.6?km of the beach and higher flow speeds (~8.8?m/s) for sites 0.8?C1.2?km inland. Flow speed calculated for sites within 0.6?km of the beach compare well with maximum velocities estimated for the largest tsunami simulation. The higher flow speeds calculated for the two sites furthest landward contrast with much lower maximum velocities (<3.8?m/s) predicted by numerical simulations. Grain size distributions of sand layers from the most distal sites are inconsistent with deposition from sediment falling out of suspension. We infer that rapid deceleration in tsunami flow and convergences in sediment transport formed unusually thick deposits. Consequently, higher flow speeds calculated by the sediment model probably overestimate the actual wave speed at sites furthest inland. 相似文献
6.
华南燕山早期晚阶段花岗岩(170~150 Ma)分布广泛,且与成矿关系密切。该时期的花岗岩具有两种不同的分布格局:在南岭东段地区以东西向分布,在武夷山地区呈北东向分布,这些花岗质岩石具有不同的地球化学特征。赣南地区出露的小岩株与钨锡成矿关系密切,具有钨锡找矿潜力,在地球化学特征上明显不同于同时代出露的大岩基。东西向展布的小岩株与同时代的大岩基可能是由时代相当于元古宙中等成熟度的陆壳富泥砂质变质沉积岩部分熔融形成,小岩株在岩浆演化过程中经历了流体相参与的高程度的分异作用,是岩浆演化到晚期阶段的产物;而北东向分布的岩体可能是由中元古代泥质变质沉积岩部分熔融所形成。该时期南岭及邻区大陆岩石圈以伸展背景为主,而整体上中国东南部大部分地区已处于东亚活动大陆边缘构造体制作用下,古太平洋板块朝东亚陆缘的北西向碰撞挤压作用已经显现。 相似文献
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8.
黄河口海床特殊的工程地质性质与复杂的工程动力稳定性问题,均与海床沉积物在波浪荷载作用下的孔压动力响应密切相关。在现代黄河水下三角洲潮间带岸滩选择4个典型研究点,现场模拟波浪作用对原状海床沉积物实施循环加载,利用孔隙水压力观测、沉积物强度测试、样品采集与实验室土工测试等方法手段,测定黄河口原状海床沉积物在循环荷载作用不同阶段的孔压响应与强度变化。研究发现,黄河口原状海床沉积物在经历循环加载过程中,典型的超孔压响应可分为逐渐累积、部分消散、快速累积、累积液化和完全消散5个阶段,分别对应沉积物强度的衰减、增大、衰减、丧失和恢复过程,沉积物的粒度组成与结构性强弱决定了超孔压的具体响应模式。波浪导致原状海床液化深度受沉积物的干密度、孔隙比、饱和度等初始物理性质影响显著,细颗粒组分的相对含量高低也在很大程度上控制着沉积物的液化特性。 相似文献
9.
The watershed of the Ningxia–Inner Mongolia reach of the Yellow River suffers serious wind erosion hazards and the areas with high wind erosion probabilities need to be identified to help in the building of the correct wind-sand blown hazard protection systems. In this study, the Integrated Wind-Erosion Modelling System model and Normalized Difference Vegetation Index (NDVI) data set were used to identify the distributions of threshold wind speeds and wind erosion occurrence probabilities. Through field observations, the relationships among NDVI, vegetation cover, frontal area (lateral cover), roughness length, and threshold friction velocity were obtained. Then, using these relationships, the spatial distributions of threshold wind speeds for wind erosion at a height of 10 m for the different months were mapped. The results show that the threshold wind speed ranged from 7.91 to 35.7 m/s. Based on the threshold wind speed distributions, the wind erosion occurrence probabilities of different months were calculated according to the current wind speed. The results show that the distributions of wind erosion occurrence probabilities and threshold wind speeds were related to each other. The resulting maps of threshold wind speeds and wind erosion occurrence probabilities would help environmental and agricultural researchers in determining some strategies for mitigating or adapting from wind erosion hazards. 相似文献
10.
准噶尔盆地西泉地区在构造上位于北三台凸起西斜坡,是有利油气聚集区。虽然已取得了一些勘探成果,但该区油藏控制因素复杂,纵横向分布规律认识不清,致使探明程度低、勘探难度大。利用钻井、测井、录井、试油、岩芯分析化验等资料,结合地震资料,查明了该区石炭系储层岩石学特征、储层特征。研究结果表明:西泉地区石炭系火山岩主要为火山熔岩类、火山碎屑岩类;火山岩储层物性北部较差,南部较好,有利储层主要是喷发相火山角砾岩、溢流相安山岩、英安岩等。该区油藏分布的主要控制因素:1)垂向上油藏主要分布于风化壳附近; 2)岩性的侧向变化控制了油藏的平面分布范围; 3)不整合面的发育与油藏的分布关系密切。进一步阐明了研究区油藏的分布规律,油气主要聚集于不整合面附近,且呈北东南西向条带状分布。油层的纵向分布与不整合面的风化淋滤带的深度有关,南北差异较大,储层的非均质性影响油藏的连片分布。 相似文献
11.
M. Felix 《Sedimentology》2002,49(3):397-419
A two‐dimensional numerical model is used to describe the flow structure of turbidity currents in a vertical plane. To test the accuracy of the model, it is applied to historical flows in Bute Inlet and the Grand Banks flow. The two‐dimensional spatial and temporal distributions of velocity and sediment concentration and non‐dimensionalized vertical profiles of velocity, turbulent kinetic energy and sediment concentration are discussed for several simple computational currents. The flows show a clear interaction between velocity, turbulence and sediment distribution. The results of the numerical tests show that flows with fine‐grained sediment have low vertical and high horizontal gradients of velocity and sediment concentration, show little increase in flow thickness and decelerate slowly. Steadiness and uniformity in these flows are comparable for velocity and concentration. In contrast, flows with coarse‐grained sediment have high vertical and low horizontal velocity gradients and high horizontal concentration gradients. These flows grow considerably in thickness and decelerate rapidly. Steadiness and uniformity in flows with coarse‐grained sediment are different for velocity and concentration. The results show the influence of spatial and temporal flow structure on flow duration and sediment transport. 相似文献
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13.
Surface sediment samples from the shelf and continental slope off southwest Africa and sediment cores from the deepest part of the Black Sea were analyzed for sterols. Because the organic matter in these anoxic sediments is relatively well-preserved, the input from source organisms in the water column is important in controlling sterol distribution patterns. The sterol distribution on the Namibian shelf is complex, probably because of the great spatial and temporal variability of biological productivity caused by seasonal upwelling and changes in oxygen concentration. The Black Sea, perhaps because of greater physical stability of the water column, has sterol distributions which can be explained by microbial activity or chemical processes acting on a constant input of organic carbon from surface production. 相似文献
14.
V. E. Zharov M. V. Sazhin V. N. Sementsov K. V. Kuimov O. S. Sazhina 《Astronomy Reports》2009,53(7):579-589
The physical origins of the apparent motion of radio sources in the ICRF are considered. The sources can be divided into four groups, according to the characteristics of their motion. Here, we consider the model for the motion of the first group of sources—those displaying uniform linear motion. Since the apparent speeds of the radio sources are close to, and sometimes exceeding, the speed of light, it is natural to suppose that these sources are relativistic jets or plasma clouds moving with speeds close to the speed of light. Uniform linear motion can be explained by a model invoking precession of the jet. We consider the physical characteristics of a number of selected sources of the ICRF in the proposed model. 相似文献
15.
贵州麻江蓝莓种植区基岩-土壤剖面元素地球化学特征 总被引：1，自引：0，他引：1
本文对麻江蓝莓核心产区种植剖面的地球化学特征进行分析,选取与蓝莓生长关系密切的K、Ca、Na、Mg、Fe、Al、Mn、Mo、Co、V、Se、Cr、Cu、Zn十四种元素作为研究对象,结果表明:土壤中元素的地球化学特征受植物根系、外援施肥、自然气候、土壤理化性质及母岩等多种因素影响。黏粒含量高的土壤剖面元素移动性较差,含量变化程度小。Se在垂直方向上的含量变化规律主要受土壤有机质含量影响,其他元素地球化学特征主要与母岩风化和淋溶作用等因素有关。基岩产状影响土壤元素在垂直方向上的变化,产状平缓的剖面各元素在下层累积较高,而基岩产状倾斜的剖面底层土壤元素随水流失,元素含量最高值大多都出现在次底层。剖面土壤中元素的地球化学特征与自然气候、土壤理化性质及母岩等因素有关,耕作层土壤元素主要受植物根系和外援施肥影响。 相似文献
16.
In this study, we present grain-size distributions of the terrigenous fraction of two deep-sea sediment cores from the SE Atlantic (offshore Namibia) and from the SE Pacific (offshore northern Chile), which we ‘unmix’ into subpopulations and which are interpreted as coarse eolian dust, fine eolian dust, and fluvial mud. The downcore ratios of the proportions of eolian dust and fluvial mud subsequently represent paleocontinental aridity records of southwestern Africa and northern Chile for the last 120,000 yr. The two records show a relatively wet Last Glacial Maximum (LGM) compared to a relatively dry Holocene, but different orbital variability on longer time scales. Generally, the northern Chilean aridity record shows higher-frequency changes, which are closely related to precessional variation in solar insolation, compared to the southwestern African aridity record, which shows a remarkable resemblance to the global ice-volume record. We relate the changes in continental aridity in southwestern Africa and northern Chile to changes in the latitudinal position of the moisture-bearing Southern Westerlies, potentially driven by the sea-ice extent around Antarctica and overprinted by tropical forcing in the equatorial Pacific Ocean. 相似文献
17.
Sediment deposition from flocculated suspensions 总被引：3，自引：0，他引：3
KATE KRANCK 《Sedimentology》1975,22(1):111-123
Suspended sediment in coastal environments with high inorganic content have characteristic broad size distributions and are composed of both single grains and flocculated aggregates. These flocculated suspensions have stable size distributions the modal size of which is dependent on the modal size of the deflocculated single grain distributions. Comparison between theoretical settling speeds of quartz grains and the settling speed of particles in natural suspensions indicates that most grains smaller than the deflocculated single grain mode settle as part of flocs, whereas the particles larger than the mode settle as single grains. As a result the size distribution curves of sediment populations which settle out during consecutive intervals are composed of a modal peak of larger grains and a low flat portion of smaller grains and resemble the asymmetrical non-normal curves common for muddy sediments. 相似文献
18.
三峡水库蓄水运用后,库区泥沙淤积将显著增加.基于三维水沙数值模型及实测资料分析,对水库蓄水初期近坝区泥沙淤积形态的成因进行了初步探讨.研究结果表明坝前淤积形态的成因既与坝前水流流态的三维特性有关,又与水库蓄水初期坝前淤积物颗粒特性有关.水库蓄水初期沉积在近坝区的泥沙颗粒较细,初始干容重较低,使得淤积物表现出一定的浮泥特性.坝前淤积总量较大主要是宽谷河段水流特性造成的;而基底深槽处淤积物厚度较大、淤积面呈水平状的主要原因则是浮泥状淤积物在重力作用下向河底运动、并沿深泓线在基底深槽中汇集. 相似文献
19.
建立薄互层地震物理模型,分别从低频和高频入射时地震记录的振幅谱形态、振幅、频率特征、AVO特征等方面入手,分析了入射频率对煤系薄互层模型地震响应特征的影响。结果表明:入射频率对薄互层层数变化反映敏感,高频入射时振幅谱形态可分辨的厚度比较小,分辨率较高;振幅谱幅值以及主频值的变化与薄互层的总厚度和波长之比有关,并且随着厚度的增加其变化规律符合薄层的振幅调谐规律与频率调谐规律;入射频率不同时,AVO曲线特征也不相同,在进行薄互层资料的对比解释及AVO分析时,要充分考虑入射频率所引起的差异。 相似文献
20.
This paper presents a simple model for tsunami sedimentation that can be applied to calculate tsunami flow speed from the thickness and grain size of a tsunami deposit (the inverse problem). For sandy tsunami deposits where grain size and thickness vary gradually in the direction of transport, tsunami sediment transport is modeled as a steady, spatially uniform process. The amount of sediment in suspension is assumed to be in equilibrium with the steady portion of the long period, slowing varying uprush portion of the tsunami. Spatial flow deceleration is assumed to be small and not to contribute significantly to the tsunami deposit. Tsunami deposits are formed from sediment settling from the water column when flow speeds on land go to zero everywhere at the time of maximum tsunami inundation. There is little erosion of the deposit by return flow because it is a slow flow and is concentrated in topographic lows. Variations in grain size of the deposit are found to have more effect on calculated tsunami flow speed than deposit thickness. The model is tested using field data collected at Arop, Papua New Guinea soon after the 1998 tsunami. Speed estimates of 14 m/s at 200 m inland from the shoreline compare favorably with those from a 1-D inundation model and from application of Bernoulli's principle to water levels on buildings left standing after the tsunami. As evidence that the model is applicable to some sandy tsunami deposits, the model reproduces the observed normal grading and vertical variation in sorting and skewness of a deposit formed by the 1998 tsunami. 相似文献