Detail study of time evolution of three thunderstorm events in Tehran area using observations and numerical simulations for lightning nowcasting

Natural Hazards - The first hourly observations of thunderclouds and associated lightning events for Tehran area are presented in this paper. Hourly data of Cloud to Ground (CG) lightning events in...     

Tectonic and climatic events controlling deposition in Tanzanian Karoo basins

The depositional megasequence of the Tanzanian Karoo resulted from an intracratonic phase of sedimentation prevailing during the maximum extension of Pangea in Late Palaeozoic and Triassic times. Karoo rocks are contained in a number of basins, extending from northeastern-most Tanzania to Lake Nyasa and beyond into neighbouring countries. The type section of the Tanzanian Karoo is the Songea Group of the Ruhuhu Basin, situated at the NE-shoulder of the Nyasa Rift. The succession, which reaches a thickness of more than 3000 m, is of Late Carboniferous to Mid-Triassic age. It exhibits five distinctive sequences, each commencing with rudaceous sediments and fining up towards the top. A sixth sequence of Middle to Late Triassic age is recognized in the Selous Basin, NE of the Ruhuhu Basin. The climate ranged from cold, semi-arid conditions in the Stephanian and Asselian to generally warm to hot climates, with fluctuating precipitation in the remaining Permian and Triassic. A marked peak in precipitation is evidenced in the Early Triassic. Each of the sedimentary sequences reflects tectonic movements related to the formation of non-volcanic rift systems during the Permian, and to detachment faults and crustal foundering during the Triassic. The intracratonic Karoo rifts were part of the Malagassy Trough, a large chasm emanating from the Tethyan margin of Gondwana in early Permian times. The Karoo rifts were terminated by their transformation to a pericratonic, passive margin in the Early Jurassic.     

Comparison of vibrocompaction methods by numerical simulations

Soils can be best compacted by repeated shearing. The strain amplitude plays an important role for the maximum compaction that can be reached. Experimental evidence emphasizes a vital impact of simultaneous multidirectional shear loading on the rate and magnitude of soil compaction. Two different vibrocompaction methods were analysed by the numerical simulations in the light of these findings. In an elastic finite element (FE) analysis, strain paths were determined. A strain amplitude‐dependent stiffness at small strains was introduced by multiple runs of the FE calculation to reach an appropriate stiffness for particular distances from the vibrator. Subsequently, the obtained strain paths were used to control single element simulations using hypoplasticity with intergranular strains. The calculated compaction profiles show three zones known from practical evidence: a limited compaction close to the vibrator, a zone of maximum compaction and a non‐densified zone remote from the vibrator. The deep vibrator produces a faster compaction than the top vibrator, especially in the more distant zone. The more efficient work of the deep vibrator can be attributed to a more general multidirectional shearing. Copyright © 2009 John Wiley & Sons, Ltd.     

A constitutive and numerical model for mechanical compaction in sedimentary basins

The aim of the paper is to provide new elements concerning the constitutive behavior of sedimentary rocks and the numerical aspects for basin simulators. A comprehensive model for mechanical compaction of sedimentary basins is developed within finite poroplasticity setting. Particular concern is paid to the effects of large porosity changes on the poromechanical properties of the sediment material. A simplified micromechanics-based approach is used to account for the stiffness increase and hardening induced by large plastic strains.A key challenge for numerical assessment of sedimentary basin evolution is to integrate multiple coupled processes in the context of open material systems. To this end, a numerical approach inspired from the ‘deactivation/reactivation’ method used for the simulation of excavation process and lining placement in tunnel engineering, has been developed. Periods of sediments accretion are simulated by progressive activation of the gravity forces within a fictitious closed system. Fundamental components of the constitutive model developed before (hydromechanical coupling, dependence of poroelastic properties on large plasticity, impact of irreversible porosity changes on the hardening rule, evolution of permeability with porosity) are included into our finite element code.Illustrative examples of basin simulation are performed in the one-dimensional case. Various aspects of the constitutive model are investigated. Their influence on the corresponding basin response is analyzed in terms of compaction law, porosity and fluid pressure profiles.     

Evaluation of numerical simulations of capillary barrier field tests

This paper presents a comparison of numerical simulations to the measured response of capillary barrier field tests. The simulations were of pilot-scale tests of four 7 m long, 1.2 m thick capillary barriers, two with 5% slopes and two with 10% slopes, with and without an included unsaturated drainage layers. The unsaturated drainage layer was included to encourage lateral drainage. The 5% sloped barriers were subjected to a period of constant infiltration for a period of 74 days, while the 10% system with the drainage layer had water added for 26 days and the conventional capillary barrier with a 10% slope was subjected to 43 days of infiltration. The numerical modelling was conducted using both drying and wetting soil moisture characteristic curves to determine their influence on the results. Differences between the field test and the model data were found, but in general the simulations appeared to adequately reproduce the response of the test systems. It was found that the use of wetting curve data provided a better fit to the field data, more accurately predicting the amount and timing of the percolate produced. © Rapid Science Ltd. 1998     

内蒙古高家梁煤矿巷道加固及围岩支护结构的数值模拟分析

高家梁煤矿位于内蒙古鄂尔多斯市东胜区东南8km处,矿井设计规模年产600×104吨。建井期间在埋深50～150m的运输大巷中部,遇到一种低强度软岩,巷道掘进与施工过程中冒顶、塌方时有发生,常规锚杆支护失效,对施工安全和进度造成很大影响。基于巷道地质情况与软岩特征,根据巷道围岩松动圈理论及围岩与支护作用关系,重点分析了软岩巷道的变形、顶板失稳机理,确定了运输大巷的工程加固方法。经过ADINA数值模拟验算以及后期的运输大巷变形监测曲线都证明加固方案满足运输大巷对支护刚度和强度的要求,同时还将加固方案进行了经济评价,得出了这种加固方案对于高家梁矿的特殊软岩巷道段加固在技术上可行,经济上可以接受的结论。     

开合构造在不同时空尺度下的地学表现

开合构造是研究地球开合运动及其构造特征,分析开合构造体系的形成机制,探索地球成因和演化的一种新假说。不同时空尺度的开合构造在地学上存在不同的表现,需要从不同角度开展研究。以亚欧非邻区巨型开合构造区、地中海大型开合构造区、东大别中型开合构造区为例,研究了开合构造理论在大地构造分区、地震活动以及现代大地测量结果解释等方面的应用。研究表明:(1)依据开合构造观点可将亚欧非邻区巨型开合构造划分为俄罗斯构造集群、非洲构造集群、北亚构造集群、中亚构造集群、南亚构造集群及东亚构造集群;(2)亚欧非邻区的强地震活动与构造集群间的新生代开合构造转换带关系密切;(3)地中海大型开合构造区内的地震剖面及震源机制揭示了地中海—土耳其—伊朗—阿富汗构造转换带现今构造运动主要以合为主;(4)东大别中型开合构造周边的狮子山、黄梅、麻城等台站的地倾斜和地应变、周边GNSS和流动重力观测结果揭示了该区周边存在时间尺度较短、量级较弱的由“合”向“开”的趋势转变,开合运动是近期诸多观测数据趋势出现准同步性变化的共同机理。     

Thermal events documented in Hadean zircons by ion microprobe depth profiles

We report the first U-Th-Pb ion microprobe depth profiles of four Hadean zircons from the Jack Hills and Mount Narryer supracrustal belts of the Narryer Gneiss Complex (NGC), Western Australia. This ultra-high spatial resolution technique probes the age and origin of sub-micron features in individual crystals that can record episodes of zircon growth. Near-surface grain dates of 2700 Ma or older are coincident with post-depositional growth/modification. Some ages may coincide with documented pre-deposition metamorphic events for the NGC and igneous emplacement at ca. 3700 Ma. Separate events that do not correlate in time with known geologic episodes prior to the preserved rock record are also present on pre-4000 Ma zircons. We find evidence for a ∼3.9 Ga event, which is coterminous within age uncertainty with one or several large basin-forming impacts (e.g. Nectaris) on the Moon attributed to the late heavy bombardment of the inner solar system.     

Evaluation of thermal equations of state for CO2 in numerical simulations

Three commonly used thermal equations of state for carbon dioxide, as well as the ideal gas law, have been compared against a large number of measurement data taken from the literature. Complex equations of state reach a higher accuracy than simple ones. The inaccuracy of the density function can cause large errors in fluid property correlations, such as heat capacity or viscosity. The influence of this inaccuracy on the results of numerical simulations have been evaluated by two examples: The first one assumes isothermal gas expansion from a volume, while the second one considers heat transport along a fracture. For both examples, different equations of state have been utilized. The simulations have been performed on the scientific software platform OpenGeoSys. The difference among the particular simulation results is significant. Apparently small errors in the density function can cause considerably different results of otherwise identical simulation setups.     

Storm waves in the Canadian Atlantic: A numerical simulation

The Grand Banks and the Scotian Shelf regions of the Canadian Atlantic often experience strong winds and high waves associated with the passage of intense storms during the winter months of December to March. These storm waves are identified as a major hazard to shipping, offshore exploration and other marine activities in eastern Canada.In this study, an operational spectral ocean wave model has been used to simulate sea-states associated with selected storm events in the Canadian Atlantic. The wave model operates on a grid (with grid spacing of about 111 km) which covers a major portion of the north Atlantic. A nested fine grid (with grid spacing of about 37 km) has been designed which covers the shelf regions of the Canadian Atlantic. The model employs deep-water physics over the coarse grid while over the fine grid shallow-water processes as represented by wave refraction, wave shoaling, bottom friction and wave number scaling are included. The wave model also includes, as an optional package, the third-generation source terms as represented by the nonlinear wave-wave interaction terms.For two selected storm events, the model generated sea-states are evaluated against available buoy data as well as against hand analyzed operational wave height charts over the northwest Atlantic. The evaluation shows that the various versions of the model can simulate the observed sea-states, reasonably well. The utility of the wave model in providing numerical guidance for offshore activities is briefly discussed.     

Field experiments and numerical simulations of whirlpool foundation pit dewatering

A whirlpool foundation pit is a small-diameter, deep circular pit. Because of its depth and small diameter, a large drawdown is required, and a limited number of wells can be installed inside the pit. During excavation, partially penetrating wells inside and outside the foundation pit have to be installed to lower the water level when the aquifer is too thick. However, partially penetrating wells near partially penetrating curtains cannot be treated by analytical methods. Therefore, it is necessary to use numerical methods to predict dewatering during excavation. Field experiments were performed on whirlpool foundation pit 1880 of Baosteel Group, Shanghai, China, to obtain pumping rates and drawdown, pumping with a single well and two wells in the confined aquifer. The results indicate that the drawdown inside the pit induced by pumping wells outside the foundation pit was small, whereas it was large for pumping wells inside the pit. The pumping wells inside and outside the pit had to be combined to lower the water level. A three-dimensional numerical model was developed to simulate the dewatering process. The hydraulic conductivities of the confined aquifers were inversed by using the pumping tests. Operation schedules were simulated with the corrected model for different combinations of wells inside and outside the pit. The results suggest that different schedules and operation conditions affect drawdown. The monitored results during dewatering indicate that the simulation and field measurements were in agreement. The results can be applied to similar situations.     

Contribution of erosion and intrusive-hydrothermal activity to the depth profile of organic matter maturation in sedimentary basins

Sharp variations in organic matter (OM) maturity with depth in sedimentary basins reflected in an abrupt increase in vitrinite reflectance (%Ro) can be caused by both the thermal effect of intrusions accelerating OM maturation in adjacent rocks and removal of a thick sedimentary layer during the extensive erosion of the basin. It is traditionally believed that the erosion of a 1.5–3.0-km-thick sedimentary layer must significantly affect the depth profile of OM maturity, resulting in a drastic increase in %Ro in the present-day sedimentary basin. Some authors used such jumps (ΔRo) to estimate the amplitude of erosion. However, our analysis showed that the depth profile of %Ro is controlled not only by the amplitude of erosion but also by sedimentation history during the posterosion stage of basin evolution. Eastern Algerian basins are good examples to examine this problem, because their evolution involved both the stage of extensive Hercynian erosion and subsequent strong hydrothermal and intrusive activity. Numerous measurements of %Ro in core samples from eastern Algerian sedimentary basins were used to analyze this problem. The calculations of %Ro(z) distributions on the basis of numerical reconstructions of the thermal history of sedimentary sections in more than 60 boreholes of the area showed that the Hercynian erosion could account for only a minor part of the observed amplitude of Δ%Ro, in spite of the significant amplitude of erosion (1.5–3.5 km) typical of the basins of the Algerian Sahara. At the same time, the intrusive and associated hydrothermal activity of the Triassic and Jurassic adequately explains the amplitude of a stepwise increase in OM maturation with depth in the present-day sedimentary sections of these basins. Thus, the reliability of erosion amplitudes estimated from jumps in depth profiles of %Ro can be assessed only after the detailed examination of the posterosion history of the basin. Original Russian Text ? Yu.I. Galushkin, M. Makhous, 2006, published in Geokhimiya, 2006, No. 12 pp. 1325–1337.     

Chemical composition of pore waters of bottom sediments in different Baikal basins

Results of study of pore waters of bottom sediments from different Baikal basins are presented. The most typical ion distribution patterns reflecting the Baikal sediment diagenesis are given. We have established that in areas with regular sedimentation, in the absence of faults and inflows, the sediment pore waters of three lake basins inherit the chemical composition of the Baikal water, which is stable in time and space. Changes in pore water composition mark general natural anomalies, such as the presence of active faults, tectonic movements, and inflows along permeable zones. In areas with the subsurface occurrence of gas hydrates, thorough long-term research has revealed an anomalous composition of pore waters. It has been established that the anomalies are caused by a discharge of deep-level mud-volcanic fluids. The ejected mud-volcanic waters differ from each other in mineralization, ion composition, and sources, which determines the difference in hydrate formation and the composition of gas hydrates.     

预应力锚索抗滑桩工程效果的数值计算评价

针对目前桩土接触问题及滑坡治理后预应力锚索抗滑桩的受力效果进行评价研究成果还很少,结合现场勘查与工程设计,根据预应力锚索抗滑桩中桩土相互作用特征,引入接触单元并编制有限元程序进行计算。根据抗滑桩锚固段的受力分布、桩体弯矩、位移及预应力因素对预应力锚索抗滑桩抗滑效果进行评价,提出预应力锚索抗滑桩的最佳预应力值,对工程设计具有一定的指导意义。     

数值模拟在沉积盆地褶皱冲断构造变形研究中的应用与发展

数值模拟是一种利用电子计算机,通过数值计算和图像显示的方法,研究工程问题、物理问题乃至自然界各类问题的方法。随着高性能计算的不断发展,数值模拟方法在沉积盆地构造变形研究中的应用不断扩大,学术界和工业界将数值模拟方法广泛应用于盆地构造变形特征与变形机制的定量研究,取得了丰硕的成果。本文在系统分析前人数值模拟成果的基础上,阐述了有限元、有限差分、边界元和离散元四种常用数值模拟实验方法的特征和应用。同时,本文对近年来数值模拟方法在沉积盆地褶皱冲断构造变形中的研究进展进行了分类总结,重点介绍这一方法在构造特征与变形机制研究中取得的成果,为数值模拟方法在盆地构造变形领域应用的不断扩大和深入提供参考。最后,本文对数值模拟技术在目前应用中面临的问题和未来的发展方向提出了一些看法和建议。     

浅水非线性长波的数值模拟与实验研究

从数值与实验两方面研究了非线性长周期水波———椭圆余弦波在浅水中的传播。根据造波板作椭圆余弦波运动速度,推导出数值模拟波浪水槽时固定入射边界上的二阶入射边界条件,计算结果表明,二阶入射边界条件对波浪的预报结果比一阶入射边界条件对波浪的预报结果更为精确。对二阶入射边界条件计算结果和实验结果的波面升高时间历程进行傅里叶分析表明,各次谐波幅值沿波浪传播方向作周期性变化,只是变化程度较小;但入射边界条件为一阶时则没有这种现象。     

A non-hydrostatic model for the numerical study of landslide-generated waves

This paper proposes and demonstrates a two-layer depth-averaged model with non-hydrostatic pressure correction to simulate landslide-generated waves. Landslide (lower layer) and water (upper layer) motions are governed by the general shallow water equations derived from mass and momentum conservation laws. The landslide motion and wave generation/propagation are separately formulated, but they form a coupled system. Our model combines some features of the landslide analysis model DAN3D and the tsunami analysis model COMCOT and adds a non-hydrostatic pressure correction. We use the new model to simulate a 2007 rock avalanche-generated wave event at Chehalis Lake, British Columbia, Canada. The model results match both the observed distribution of the rock avalanche deposit in the lake and the wave run-up trimline along the shoreline. Sensitivity analyses demonstrate the importance of accounting for the non-hydrostatic dynamic pressure at the landslide-water interface, as well as the influence of the internal strength of the landslide on the size of the generated waves. Finally, we compare the numerical results of landslide-generated waves simulated with frictional and Voellmy rheologies. Similar maximum wave run-ups can be obtained using the two different rheologies, but the frictional model better reproduces the known limit of the rock avalanche deposit and is thus considered to yield the best overall results in this particular case.     

东非海岸重点盆地渐新世构造事件—沉积体系耦合关系研究

本论文以东非海岸鲁伍马、坦桑尼亚及拉穆盆地为对象，利用钻井、测井及地震资料，揭示了渐新世构造事件—古地貌特征—沉积系统的耦合关系，服务研究区油气勘探选区。结果表明，（1）板块构造事件控制宏观地貌格局及沉积环境变化。随着印度—塞舌尔板块与非洲板块分离，印度洋逐渐扩张，海水南侵，沉积环境由陆相变为海相。由于Afar地幔柱作用及地层抬升等作用，东非海岸整体呈西高东低地貌格局；（2）洋中脊扩展及断层活动控制盆地隆坳格局及沉积体系宏观展布规律。研究区发育西部坳陷带、中部斜坡带及东部深海平原带，东部Davie东及Davie西断层构成Davie构造带。从西向东依次发育 4 大河流—三角洲—海底扇沉积体系；西部坳陷带以三角洲沉积为主，中部斜坡带发育海底扇，东部深海平原带以半深海—深海泥最为常见，沉积体系多发育在Davie构造带以西；（3）次级断层活动影响沉积体系的发育规模及分布。沉积体系多发育在西部坳陷带及中部斜坡带的凹陷中。因凹陷及次级断裂影响，鲁伍马盆地北部、坦桑尼亚盆地南部沉积体系呈北偏特征，而拉穆盆地具南偏趋势。