Simulation of individual particle movement in a gravel streambed     

J. Mikael Malmaeus  Marwan A. Hassan 《地球表面变化过程与地形》2002,27(1):81-97

A two‐dimensional simulation model of travel distances of individual particles in a gravel‐bed river is presented. The model is based on a number of rules, which include particle size, entrainment, trajectory, distance of movement and entrapment. Particle interactions are controlled by resistance fields defined about each obstacle and critical elevation defined in the model. Resistance fields, particle dropping and critical elevation rules control particle interactions. The interaction rules cause the particles to develop pebble clusters, stone cells and transverse structures (transverse ribs). The simulated travel distances of individual particles are consistent with reported field results. Individual particle travel distances were simulated using two different models; one without interactions between the individual particles and the stationary bed and one with interactions. The case without interactions demonstrates the random nature of sediment transport, and narrow ranges of travel distances. Wider ranges of travel distances, similar to those for natural situations, were obtained for the cases with interactions. The more intense the interaction between the mobile stones and the stationary ones, the wider the range of distances of travel for a given particle size. Modelling the mean travel distance yielded a result similar to that published previously, which was based on empirical data. Well developed bed‐surface structures were obtained for relatively poorly sorted sediment with intense interactions between particles. Transverse structures developed when relatively large particles were allowed to move. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

The significance of rock structure,lithology and pre‐glacial deep weathering for the shape of intermediate‐scale glacial erosional landforms     

Mats Olvmo  Magnus Johansson 《地球表面变化过程与地形》2002,27(3):251-268

The main landforms within the glacially scoured Precambrian rocks of the Swedish west coast are closely connected to the principal structural pattern and have lately been explained as mainly a result of etch processes, probably during the Mesozoic and with a possible second period of etching during the Neogene. To explore the effect of multiple glacial erosion on the rock surfaces, an island with two different lithologies and with striae from different directions was selected for a detailed study, focusing on the shape of roches moutonnées. Air‐photo interpretation of bedrock lineaments and roches moutonnées combined with detailed field mapping and striae measurements are used to interpret the structural and lithological control on the resulting shape. The study reveals a significant difference in shape between roches moutonnées in augen‐granite and orthogneiss. Low elongated and streamlined roches moutonnées occur in the gneiss area, striated by a Late Weichselian ice flow from the NE. This ice flow is subparallel with both the local dominant trend of topographically well‐expressed joints and the schistosity of the gneiss. Frequently, there are no signs of quarrying on the lee‐sides of the gneiss roches moutonnées and hence they resemble the shape of whalebacks, or ruwares, as typically associated with the exposed basal weathering surface found in tropical areas. The granite roches moutonnées were formed by an older ice flow from the ESE, which closely followed the etched WNW–ESE joint system of the granite. Late Weichselian ice flow from the NE caused only minor changes of the landforms. On the contrary, marks of the early ESE ice flow are poorly preserved in the gneiss area, where it probably never had any large effect as the flow was perpendicular to both schistosity and structures and, accordingly, also to the pre‐glacial relief. The study demonstrates that coincidence between ice flow direction and pre‐glacially etched structures is most likely to determine the effects of glacial erosion. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Spatial and temporal variability of pore‐water pressures in residual soil slopes in a tropical climate     

R. B. Rezaur  H. Rahardjo  E. C. Leong 《地球表面变化过程与地形》2002,27(3):317-338

It is critical to understand and quantify the temporal and spatial variability in hillslope hydrological data in order to advance hillslope hydrological studies, evaluate distributed parameter hydrological models, analyse variability in hydrological response of slopes and design efficient field data sampling networks. The spatial and temporal variability of field‐measured pore‐water pressures in three residual soil slopes in Singapore was investigated using geostatistical methods. Parameters of the semivariograms, namely the range, sill and nugget effect, revealed interesting insights into the spatial structure of the temporal situation of pore‐water pressures in the slopes. While informative, mean estimates have been shown to be inadequate for modelling purposes, indicator semivariograms together with mean prediction by kriging provide a better form of model input. Results also indicate that significant temporal and spatial variability in pore‐water pressures exists in the slope profile and thereby induces variability in hydrological response of the slope. Spatial and temporal variability in pore‐water pressure decreases with increasing soil depth. The variability decreases during wet conditions as the slope approaches near saturation and the variability increases with high matric suction development following rainfall periods. Variability in pore‐water pressures is greatest at shallow depths and near the slope crest and is strongly influenced by the combined action of microclimate, vegetation and soil properties. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

喀什"奇异震群"与构造地震的对比研究     

夏爱国  刘永廷  缑兰兰 《内陆地震》2002,16(3):193-204

20 0 1年 11月 14、 15日新疆喀什台记录到 86次振动事件 (“奇异震群”事件 )。为识别其性质 ,应用波谱分析、偏振分析等方法 ,对该事件和同范围构造地震的地震波特征进行了对比研究 ,发现 :(1)喀什“震群”的全波列衰减比构造地震的全波列衰减快很多 ;(2 )与构造地震的速度谱相比 ,“震群”的频谱相对较为“集中”,而构造地震的则较为“发散”;(3)“震群”位移谱的拐角频率和卓越频率均较构造地震的相应量高出一倍多 ,且离散较小。通过对喀什“奇异震群”这些特征进行分析研究 ,认为这一事件极有可能是人工事件  相似文献   

泾阳4.8级地震的构造背景   总被引：12，自引：1，他引：12       下载免费PDF全文

王卫东 《地震工程学报》2002,24(2):145-149

1998年1月5日烃阳Ms 4.8地震是陕西省近40年来发生的最大一次地震。研究了此次地震的构构背景和地球物理场特征。  相似文献   

Sea cliffs resulting from late Miocene extensional tectonics: the Serra Gelada case study (Betic Cordillera, Spain)     

Alfonso Ybenes  Pedro Alfaro  Jos Delgado  Antonio Estvez  Jesús M. Soria 《Geomorphology》2002,42(3-4)

The Serra Gelada sea cliffs are carved in Mesozoic carbonate rocks belonging to the External Zones of the eastern Betic Cordillera (Alicante, SE Spain). Several normal faults with vertical slips of more than a hundred metres have played an important role in the origin of this coastline. Some previous studies propose that the present cliff morphology was mainly originated by Quaternary fault activity. However, the integration of geomorphological features, stratigraphical and sedimentological data, together with the results of the tectonic analysis of fractures occurring in Serra Gelada, and a detailed study of seismic reflection profiles carried out in the adjacent continental shelf, indicate that these normal faults were active mainly during the late Miocene. Therefore, the Serra Gelada sea cliffs represent a tectonically controlled long-term landscape. Thus, normal faults have not significantly modified the Serra Gelada relief since then. Furthermore, the northern part of the Serra Gelada cliff may be considered as an inherited pre-Quaternary relict palaeocliff since it has only undergone very little erosive recession.  相似文献   

Effective timescales of coupling within fluvial systems   总被引：1，自引：0，他引：1  

Adrian M. Harvey   《Geomorphology》2002,44(3-4)

This paper presents a review of the coupling concept in fluvial geomorphology, based mainly on previously published work. Coupling mechanisms link the components of the fluvial system, controlling sediment transport down the system and the propagation of the effects of base-level change up the system. They can be viewed at several scales: at the local scale involving within-hillslope coupling, hillslope-to-channel coupling, and within-channels, tributary junction and reach-to-reach coupling. At larger scales, coupling can be considered as zonal coupling, between major zones of the system or as regional coupling, relating to complete drainage basins. These trends are illustrated particularly by the examples of hillslope-to-channel coupling in the Howgill Fells, northwest England, badland systems in southeast Spain, alluvial fans in Spain, USA and UAE, and base-level-induced dissection of Neogene sedimentary basins in southeast Spain. As the spatial scales increase, so do the timescales involved. Effective temporal scales relate to magnitude and frequency characteristics, recovery time and propagation time, the relative importance changing with the spatial scale. For downsystem coupling at the local scale, the first two are important, with propagation time increasing in importance in larger systems, especially in those involving upsystem coupling related to base-level change. The effective timescales range from the individual event, with a return period of decades, through decadal to century timescales for downsystem coupling, to tens to hundreds of thousands of years for the basinwide response to base-level change. The effective timescales influence the relative importance of factors controlling landform development.  相似文献   

Sectoral Shifts and Occupational Migration in the United States     

Mark E. Reisinger 《The Professional geographer》2003,55(3):383-395

This research is grounded in notions of differential economic restructuring across employment sectors and geographic space, as well as migration selectivity by occupation. A series of unconstrained competing‐destinations models were employed to analyze the response by workers in thirteen occupational categories to sectoral employment change, average wages, and distance. As was hypothesized, workers in occupations that require high levels of education and skills are more responsive, in terms of migration, to economic opportunities in alternative labor‐market areas. However, the results do not support the hypothesis that highly educated and skilled workers migrate longer distances. Further investigation suggests that opportunities for highly educated and skilled workers may be clustering in relatively few areas that are in relatively close proximity.  相似文献   

Characteristics of Tectonic Deformation and Mechanisms for the Active Maxianshan-Xinglongshan Fault System in the Lanzhou Area     

Yuan Daoyang  Liu Xiaofeng  ZHENG Wenjun  Liu Xiaolong  Liu Baichi 《中国地震研究》2003,17(4):315-323

A detailed investigation permitted us to obtain quantitative data concerning fine geometric structures of 4 faults of the active Maxianshan-Xinglongshan fault system and the latest movement along them. Of them the northern Maxianshan border fault is a large-scale, strongly active Holocene reverse sinistral strike-slip fault, the other 3 faults, the southern Maxianshan border fault and the southern Xinglongshan border and the northern Xinglongshan border faults are the accompanying active late-Pleistocene thrust faults, which are incorporated into the main strike-slip fault, the northern Maxianshan border fault at depth. It is the most important earthquake-controlling fault in the Lanzhou area, the fault influences and constrains the seismic activity in the area.  相似文献   

Scattering of elastic waves by a general anisotropic basin. Part 2: a 3D model     

Marijan Dravinski 《地震工程与结构动力学》2003,32(5):653-670

Scattering of plane harmonic waves by a three‐dimensional basin of arbitrary shape embedded within elastic half‐space is investigated by using an indirect boundary integral equation approach. The materials of the basin and the half‐space are assumed to be the most general anisotropic, homogeneous, linearly elastic solids without any material symmetry (i.e. triclinic). The unknown scattered waves are expressed in terms of three‐dimensional triclinic time harmonic full‐space Green's functions. The results have been tested by comparing the surface response of semi spherical isotropic and transversely isotropic basins for which the numerical solutions are available. Surface displacements are presented for a semicircular basin subjected to a vertical incident plane harmonic pseudo‐P‐, SV‐, or SH‐wave. These results are compared with the motion obtained for the corresponding equivalent isotropic models. The results show that presence of the basin may cause significant amplification of ground motion when compared to the free‐field displacements. The peak amplitude of the predominant component of surface motion is smaller for the anisotropic basin than for the corresponding isotropic one. Anisotropic response may be asymmetric even for symmetric geometry and incidence. Anisotropic surface displacement generally includes all three components of motion which may not be the case for the isotropic results. Furthermore, anisotropic response strongly depends upon the nature of the incident wave, degree of material anisotropy and the azimuthal orientation of the observation station. These results clearly demonstrate the importance of anisotropy in amplification of surface ground motion. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献