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1.
Vincenzo Cuomo Vincenzo Lapenna Maria Macchiato Carmine Serio & Luciano Telesca 《Geophysical Journal International》1999,139(3):889-894
We explore the inner dynamics of daily geoelectrical time series measured in a seismic area of the southern Apennine chain (southern Italy). Autoregressive models and the Higuchi fractal method are applied to extract maximum quantitative information about the time dynamics from these geoelectrical signals. First, the predictability of the geoelectrical measurements is investigated using autoregressive models. The procedure is based on two forecasting approaches: the global and the local autoregressive approximations. The first views the data as a realization of a linear stochastic process, whereas the second considers the data points as a realization of a deterministic process, which may be non-linear. Comparison of the predictive skills of the two techniques allows discrimination between low-dimensional chaos and stochastic dynamics. Our findings suggest that the physical systems governing electrical phenomena are characterized by a very large number of degrees of freedom and can be described only with statistical laws. Second, we investigate the stochastic properties of the same geoelectrical signals, searching for scaling laws in the power spectrum. The spectrum fits a power law P ( f )∝ f −α , with the scaling exponent α a typical fingerprint of fractional Brownian processes. In this analysis we apply the Higuchi method, which gives a linear relationship between the fractal dimension D Σ and the spectral power law scaling index α : D Σ =(3− α )/2. This analysis highlights the stochastic nature of geoelectrical signals recorded in this seismic area of southern Italy. 相似文献
2.
The focus of this paper is to relate fundamental statistical properties of landforms and drainage networks to models that have been developed in statistical physics. Relevant properties and models are reviewed and a general overview is presented. Landforms and drainage networks are clearly complex, but well-defined scaling laws are found. Coastlines, topography contours, and lakes are classic self-similar fractals. The height of topography along a linear track is well approximated as a Brownian walk, a self-affine fractal. This type of behavior has also been found in surface physics, for example the surface roughness of a fracture. An applicable model is the Langevin equation, the heat equation with a stochastic white-noise driver. This model also reproduces the statistics of sediment deposition. Drainage networks were one of the original examples of self-similar fractal trees. An important advance in quantifying the structure of drainage networks is the application of the Tokunaga fractal side-branching statistics. A classic problem in statistical physics is the diffusion-limited aggregation. The resulting tree like structures have been shown to also satisfy the Tokunaga statistics. A modified version of the diffusion-limited aggregation model reproduces the statistics of drainage networks. It is concluded that the models developed in statistical physics have direct applicability to the fundamental problems in geomorphology. 相似文献
3.
莱州湾东岸发育有分形特征典型的小尺度河流,受区域内陆海相互作用影响显著。基于前人对莱州湾东岸的研究以定性描述为主,而缺乏定量分析这一现状,以莱州湾东岸3条典型河流为例,采用分形分析和GIS技术相结合的方法,对区域内流域地貌特征进行了定量分析。结果表明,分形分析同样适用于研究小尺度河流,可很好地揭示区域内陆海相互作用特征及流域地貌所处的发育阶段。基于分形方法所反映的流域地貌特征与数字高程模型所提取的流域地貌信息较吻合,最终结果能较客观地反映出流域地貌的发育特征。 相似文献
4.
Surface-process models (SPMs) have the potential to become an important tool in predicting sediment flux to basins, but currently suffer from a lack of quantitative understanding of their controlling parameters, as well as difficulties in identifying landscape properties that can be used to test model predictions. We attempt to constrain the parameter values that enter a SPM by comparing predictions of landscape form (as expressed by hypsometric and fractal measures) and process rates obtained for different parameter sets with observations from the south-eastern Australian highlands, a rifted margin mountain belt that has remained tectonically stable during Cenozoic times. We map the hypsometry and fractal characteristics of south-eastern Australia and find that the roughness amplitude (G) correlates well with local relief, whereas the hypsometric integral (H ) correlates slightly better with elevation than with relief. The fractal dimension (D) does not correlate with any other morphometric measure and varies randomly throughout the region. Variograms generally show three kinds of scaling behaviour of topography with increasing wavelength, with topography only being truly self-affine at wavelengths between ～1 and 10 km. From a review of the available data on long-term denudation rates in south-eastern Australia, we infer that these have been 1–10 m Myr?1, and average escarpment retreat rates 0.2–1.0 km Myr?1, throughout the Cenozoic. Model predictions, using a SPM that includes hillslope diffusion and long-range fluvial transport, suggest that landscape form evolves with time; after an initial phase where D, G and relief increase, all morphometric measures decrease with increasing denudation. The behaviour of GandH in the models is qualitatively compatible with the observations; D, however, varies predictably in the models, in contrast with its random behaviour in the real world. The observed present-day morphology of SE Australia does not impose quantitative constraints on parameter values. The fractal analyses do impose general conditions of relative parameter values that have to be met in order to create ‘realistic’ topographies. They also suggest that there is no theoretical basis for including hillslope diffusion in SPMs with a spatial resolution coarser than 1 km. A comparison of the observed denudation and retreat rates with model predictions places order-of-magnitude constraints on parameter values. Thus, data pertaining to landscape evolution are much more valuable than static present-day topography data for calibrating SPMs. 相似文献
5.
Relative size of fluvial and glaciated valleys in central Idaho 总被引：2，自引：1，他引：1
Quantitative comparisons of the morphometry of glaciated and fluvial valleys in central Idaho were used to investigate the differences in valley relief and width in otherwise similar geologic and geomorphic settings. The local relief, width, and cross-sectional area of valleys were measured using GIS software to extract information from USGS digital elevation models. Hillslope gradients were also measured using GIS software. Power-law relationships for local valley relief, width, and cross-sectional area as a function of drainage area were developed. Local valley relief in glaciated valleys relates to drainage area with a power-law exponent similar to fluvial valleys, but glaciated valleys are deeper for a given drainage area. Local valley width in glaciated valleys is greater than in fluvial valleys, but the exponent of the power-law relationship to drainage area is similar in both valley types. Local valley cross-sectional area in glaciated valleys increases with drainage area with a power-law exponent similar to fluvial valleys, however, glacial valleys have roughly 80% greater cross-sectional area. Steep valley walls in glaciated basins increase the potential for bedrock landsliding relative to fluvial basins. Both the Olympic Mountains of Washington and valleys in central Idaho show relationships in which glaciated valleys are up to 30% deeper than fluvial valleys despite differences in lithology, tectonic setting, and climate. 相似文献
6.
干旱河谷地带的水热状况和气候特征等与山地地形、河谷深切为主的地貌格局有密切关系。干旱河谷的形成,是在独特自然区位和复合性低纬大气环流系统的环境条件下,受梯度地形、山谷相间和地形环境等地表因素共同影响下的结果。新生代时期以来的造山运动与河谷地貌演变是局部地带＂荒漠化＂气候环境形成的重要因素,并引发其它相关生态因子和整体生态系统产生变化,在低凹盆谷和河流峡谷出现了脆弱易退化、环境特异性、环境要素亏缺为特征的特殊生态系统。 相似文献
7.
砒砂岩区地貌形态三维分形特征量化及空间变异 总被引：3，自引：0，他引：3
针对现有地貌形态三维分形模型结构存在的不足,构建一个新的地貌形态三维分形维数测算模型。基于该模型对砒砂岩区274个小流域的地貌形态三维分形维数进行计算并分析其空间变异规律。研究表明：① 基于该模型计算的分形维数能更准确地反映地貌形态复杂度信息;② 砒砂岩区小流域地貌形态三维分形维数介于1.683 6~1.948 6之间;③ 地貌形态三维分形维数整体上覆土砒砂岩区（均值为1.765 9）<裸露砒砂岩强度侵蚀区（均值为1.785 4）和剧烈侵蚀区（均值为1.774 8）<覆沙砒砂岩区（均值为1.796 6）。由于地表覆盖物、砒砂岩裸露程度和土壤侵蚀机理的差异而形成的不同地貌特征是该区地貌形态分形特征空间变异的主要原因。 相似文献
8.
泥河湾保护区地貌特征与地质灾害 总被引：4，自引：0，他引：4
根据泥河湾保护区实地调查,黄土台地、黄土沟梁和河谷地貌是发育在“泥河湾层”及其覆地层上的主要地貌类型,其形态特征和形态测量反映了该区流水地貌的现代演化特征。伴随流水地质作用与地貌演化发生的水土流失、泥石流、崩塌和地面塌陷等地质灾害危及保护区的地层剖面。笔者认为该区域地质灾害是多种致灾因素造成的,其中的主导因素是气候、植被和人为因素,通过控制植被因素可以改变目前的地质环境状况。 相似文献
9.
Soil erodibility and processes of water erosion on hillslope 总被引：14，自引：0，他引：14
The importance of the inherent resistance of soil to erosional processes, or soil erodibility, is generally recognized in hillslope and fluvial geomorphology, but the full implications of the dynamic soil properties that affect erodibility are seldom considered. In Canada, a wide spectrum of soils and erosional processes has stimulated much research related to soil erodibility. This paper aims to place this work in an international framework of research on water erosion processes, and to identify critical emerging research questions. It focuses particularly on experimental research on rill and interrill erosion using simulated rainfall and recently developed techniques that provide data at appropriate temporal and spatial scales, essential for event-based soil erosion prediction. Results show that many components of erosional response, such as partitioning between rill and interrill or surface and subsurface processes, threshold hydraulic conditions for rill incision, rill network configuration and hillslope sediment delivery, are strongly affected by spatially variable and temporally dynamic soil properties. This agrees with other recent studies, but contrasts markedly with long-held concepts of soil credibility as an essentially constant property for any soil type. Properties that determine erodibility, such as soil aggregation and shear strength, are strongly affected by climatic factors such as rainfall distribution and frost action, and show systematic seasonal variation. They can also change significantly over much shorter time scales with subtle variations in soil water conditions, organic composition, microbiological activity, age-hardening and the structural effect of applied stresses. Property changes between and during rainstorms can dramatically affect the incidence and intensity of rill and interrill erosion and, therefore, both short and long-term hillslope erosional response. Similar property changes, linked to climatic conditions, may also significantly influence the stability and resilience of plant species and vegetation systems. Full understanding of such changes is essential if current event-based soil erosion models such as WEPP and EUROSEM are to attain their full potential predictive precision. The complexity of the interacting processes involved may, however, ultimately make stochastic modelling more effective than physically based modelling in predicting hillslope response to erodibility dynamics. 相似文献
10.
The seafloor topography of a slow-spreading ridge shows a number of well-documented regularities at the ridge segment scale as the result of the complex interplay between ridge-axis magmatic and tectonic processes. This paper describes the results of a detailed analysis of the seafloor topography of the Mid-Atlantic Ridge near the Atlantis transform, where marine gravity data provide independent, although non-unique, constraints on subseafloor density structure. Using a combined topography and gravity data set, we identified the specific contributions of subseafloor density structure to the seafloor topography. We show that the observed along-axis deepening (0.3–0.8 km) from the midpoint of a ridge segment towards the non-transform offsets in the study area can be explained by the vertical deflection of a zero-age plate in response to along-axis crustal thickness variations. However, this effect can only account for 50–60 per cent of the observed 1.5–1.7 km deepening towards the Atlantis transform, suggesting the presence of significant stresses in the lithosphere near a transform. Results of plate flexural calculations also predict a more elevated rift flank at the inside corner of the ridge–transform intersection than at the conjugate outside corner. Such an asymmetry in rift flank topography is calculated to be greatest near a transform fault with a significant volume of deep transform valley and when adjacent plates across the transform fault are mechanically decoupled or only weakly coupled. Together these results illustrate the complex interplay between various tectonic processes at a slow-spreading ridge. 相似文献
11.
2015年12月召开的中央城市工作会议提出“在中西部地区培育发展一批城市群、区域性中心城市,让中西部地区广大群众在家门口也能分享城镇化成果”。黄土高原是我国水土流失最严重和生态环境最敏感的地区之一,地貌水系特征对其城镇化建设尤为重要。从黄土高原独特的分形地貌入手,以无定河流域为研究对象,探究城乡居民点与地貌水系的耦合关系。分形维数上,通过盒维数法测算出19处小流域沟道水系分形维数,并分析城乡居民点的数量、等级与沟道分形维数的内在联系。空间上,采取缓冲区分析居民点与沟道水系的临近关系并探究水系与居民点等级对应特征。研究发现：在数理分析上,（1）各小流域的分形维数越高,单位面积的居民点数量越多;沟道分形维数一定时,高等级居民点的出现会降低沟道内单位面积低级别居民点数量。（2）河谷沟道的分形维数达到1.223是沟道内出现县城的必要而不充分条件。在空间分析上,（3）城乡居民点分布与分形沟道水系相临近,并且居民点等级分布规律具有自相似性、层级迭代性。基于以上特征探索具有地域特色的镇村体系布局模式,以期为该地区城镇建设提供理论依据。 相似文献
12.
Discovery of an ice cave in the Yatude Valley, Langhovde, Dronning Maud Land, East Antarctica 总被引：1，自引：0，他引：1
A circular hole was discovered on the downstream side of a glacier dam in the Yatude Valley, Langhovde, East Antarctica, during the 2005–2006 austral summer. The opening of this hole is the first opportunity enabling us to observe the interior of the dam. The opening led to a large cave in the dam, raising the possibility of meltwater drainage through the dam. The Yatude Valley is an approximately U-shaped fluvial valley. The valley floor has been incised to form a box-shaped inner valley that contains fluvial terraces and large boulders upon the valley floor. The origin of these features can be explained by a large amount of running water; however, we consider it unlikely that a regular current has flowed through this site for a long period. Instead, it is more likely that large quantities of lake water have been periodically discharged due to collapse of the glacier dam or spilling out through a tunnel channel within the cave. The discovered hole and the ice cave are key features in understanding the historical development of the Yatude Valley in relation to the melting history of the Antarctic ice sheet. 相似文献
13.
Since 2005,dozens of geographical observational stations have been established in the Heihe River Basin(HRB),and by now a large amount of meteorological,hydrological,and ecological observations as well as data pertaining to water resources,soil and vegetation have been collected.To adequately analyze these available data and data to be further collected in future,we present a perspective from complexity theory.The concrete materials covered include a presentation of adaptive multiscale filter,which can readily determine arbitrary trends,maximally reduce noise,and reliably perform fractal and multifractal analysis,and a presentation of scale-dependent Lyapunov exponent(SDLE),which can reliably distinguish deterministic chaos from random processes,determine the error doubling time for prediction,and obtain the defining parameters of the process examined.The adaptive filter is illustrated by applying it to obtain the global warming trend and the Atlantic multidecadal oscillation from sea surface temperature data,and by applying it to some variables collected at the HRB to determine diurnal cycle and fractal properties.The SDLE is illustrated to determine intermittent chaos from river flow data. 相似文献
14.
Summary. The quality of marine magnetic anomaly sources is described with the power-density representation of a stochastic model of random temporal and spatial emplacement of the marine magnetic anomaly source in the oceanic crust. Typical values of sea-floor spreading and emplacement parameters define a high-fidelity process of recording and sea-surface detection of the palaeomagnetic field reversals for spreading rates over 20 mm yr-1 . An analogous stochastic model is developed for the formation of sea-floor topography by normal faulting. It is shown that the random process of normal faulting observed in the inner walls of the FAMOUS rift valley can account for the quality of the adjacent West Rift Mountains topography. 相似文献
15.
H. Jesse Walker 《自然地理学》2013,34(4):373-375
The focus of this research is the development of a model which explains channel pattern variability in streams. Since channel pattern is commonly regarded as a qualitative phenomenon, the research employs a logistic regression model, which is advocated as an alternative to traditional graphic/discriminant analysis, since the concepts of threshold and instability have very natural expressions in the logistic regression framework. The results demonstrate that channel gradient and mean discharge can effectively explain channel pattern (i.e., whether the channel is single or multithreaded) in an environment where there is a small range of bed material size. Sediment sorting is also shown to be related to channel pattern in the study environment. Models using valley gradient rather than channel gradient are shown to be distinctly inferior, and no advantage is found in using a stream power measure as opposed to separate gradient and discharge measures. [Key Words: fluvial geomorphology, stream channels, channel patterns, models.] 相似文献
16.
James P. Terry 《Singapore journal of tropical geography》1999,20(1):86-98
This paper examines features of drainage and stream channel form and process on the mountainous volcanic island of Kadavu in the humid tropical South Pacific, and interprets the findings in relation to island environmental characteristics such as geology, regolith soils, topography, vegetation and climate. At island and sub-island scales, drainage patterns are linked to the geographical arrangement and topography of the late Cenozoic volcanoes. Stream channel and bedload characteristics demonstrate the importance of both deep saprolite weathering profiles for supplying sediment into the fluvial system, and the high energy nature of the fluvial transport regimes. Landscape chemical denudation is estimated at 50-85 mm per 1,000 years from baseflow solute concentrations converted from water conductivity readings.
Relative tectonic and sea-level stability during the late Holocene and the largely undisturbed rainforest and savanna vegetation on the island suggest that climatic factors control rates of fluvial processes on Kadavu. Streamflow records show particularly that tropical storms can have a big impact. The effects of possible increasing numbers of cyclones in the South Pacific and human vegetation disturbance on Kadavu are considered. 相似文献
Relative tectonic and sea-level stability during the late Holocene and the largely undisturbed rainforest and savanna vegetation on the island suggest that climatic factors control rates of fluvial processes on Kadavu. Streamflow records show particularly that tropical storms can have a big impact. The effects of possible increasing numbers of cyclones in the South Pacific and human vegetation disturbance on Kadavu are considered. 相似文献
17.
Goro Komatsu John W. Olsen Jens Orm Gaetano Di Achille David A. Kring Takafumi Matsui 《Geomorphology》2006,74(1-4):164-180
The Tsenkher structure, in the Gobi-Altai region of Mongolia, was studied using a wide array of remote sensing data and field observations. The structure has a shallow, 3.6 km wide, central depression bordered by a near-circular ridge (putative crater rim) with breaches to the northwest. The central depression is obliterated partially by fluvial infill through these breaches. Outside the ridge, the western side is a rugged terrain, but the eastern half is characterized by a concentric outer ridge that occurs at about one radius distance from the inner ridge. Although intrusion, salt tectonics and maar crater hypotheses cannot be completely ruled out, its morphology strongly implies an impact origin for the Tsenkher structure. If of impact origin, it has a well-preserved morphology and its position in the basin fills indicates that the formation may have occurred relatively recently, sometime during the late Tertiary or Quaternary. The outer ridge morphology is similar to rampart craters on Mars, whose formation has been attributed to fluidization of a water-rich target layer and ejecta materials, or to atmospheric entrainment and deposition of ejected materials. However, other hypotheses including erosional remnant of ejecta blanket, erosional scarp of structural rim uplift, multi-ring or deeply eroded crater rim of a peak-ring crater are also possible at this stage. A complex fluvial and probable lacustrine history is envisaged within the Tsenkher structure. The structure is also associated with archaeology, including Paleolithic and Bronze Age remains. 相似文献
18.
During break-up in the High Arctic, ice jams are insignificant, but large quantities of snow accumulated in the valleys strongly affect fluvial processes. Near Resolute, Cornwallis Island, many channels were first formed in valley snow drifts and their positions were unstable. Channels carved in the snow can easily accommodate changing discharge by a modification of their width, depth, and velocity. This causes considerable variation in the at-a-station hydraulic geometry relationships. The availability of sediment is locally restricted by the snow lining along the channels, although some fluvial sediments deposited on the snow revealed that peak flows could entrain very large boulders. Several depositional features observed in the study area also indicated that fluvial activities can extend over a broad zone beyond the confines of the summer channels. This study suggests that, by increasing discharge, snow jams enhance the erosional power of streams, but by interposing between streamflow and the valley floor, the snow can limit the supply of sediments. Whether the erosional or the protectional tendency dominates will depend upon the snow jam characteristics along various segments of the High Arctic streams. 相似文献
19.
Tectonic control of the Tejo river fluvial incision during the late Cenozoic, in Ródão—central Portugal (Atlantic Iberian border) 总被引：2，自引：0，他引：2
Staircases of strath terraces and strongly incised valleys are the most typical landscape features of Portuguese rivers. This paper examines the incision achieved during the late Cenozoic in an area crossed by the Tejo river between the border with Spain and the small town of Gavião. In the more upstream reach of this area, the Tejo crosses the Ródão tectonic depression, where four levels of terraces are distinguished. During the late Cenozoic fluvial incision stage, the Ródão depression underwent less uplift than the adjacent areas along the river. This is reflected by the greater thicknesses and spatial extent of the terraces; terrace genesis was promoted by impoundment of alluvium behind a quartzitic ridge and the local presence of a soft substratum. Outside this tectonic depression, the Tejo has a narrow valley incised in the Hercynian basement, with some straight reaches that probably correspond to NE–SW and NNW–SSE faults, the terraces being nearly absent. Geomorphological evidence of tectonic displacements affecting the Ródão dissected terrace remnants is described. Geochronological dating of the two younger and lower terrace levels of this depression suggests a time-averaged incision rate for the Tejo in the Ródão area, of ca. 1.0 m/ka over the last 60 thousand years. A clear discrepancy exists between this rate and the 0.1 m/ka estimated for the longer period since the end of the Pliocene. Although episodes of valley incision may be conditioned by climate and base-level changes, they may also have been controlled by local factors such as movement of small fault-bounded blocks, lithology and structure. Regional crustal uplift is considered to be the main control of the episodes of valley incision identified for this large, long-lived river. A model is proposed in which successive regional uplift events—tectonic phases—essentially determined the long periods of rapid river downcutting that were punctuated by short periods of lateral erosion and later by some aggradation, producing strath terraces. 相似文献