地震活动性的细胞自动机模型   总被引：8，自引：0，他引：8       下载免费PDF全文

刘桂萍  石耀霖  马丽 《地震工程学报》1995,17(2):20-25

本文在二维平面设计了一个模拟地震活动性的细胞自动机模型，分析了模拟地震离列的活动性，并探讨了强震前场兆和源兆的物理机制，结果表明，模型的地震序列很好地反映了实际地震的丛集特性、幂律关系和空间转移概率的稳定性等特点。  相似文献   

Asymmetry of river channel cross-sections: Part II. mode of development and local variation     

A. D. Knighton 《地球表面变化过程与地形》1982,7(2):117-131

A five-stage model of the development of cross-sectional asymmetry is proposed in which alternating bar deposition and bed scour are important elements. Quasi-periodic reversals in the sense of asymmetry and a progressive increase in the magnitude of asymmetry at sections which develop an asymmetry initially are major features of the model. Application of Bridge's (1977) model confirms several features of the model and suggests that the degree of asymmetry is directly related to bend curvature. After the initial stages, subsequent changes to the cross-sectional and planimetric form of the channel may be intensified by the developing asymmetry through a system of positive feedbacks in which the levels of form and flow distortion are interrelated. Asymmetry appears to provide an important link between cross-sectional and plan form adjustment. Spatial series of asymmetry obtained for three lengths along a mountain stream contain features predicted by the model. In particular, the dominant peak in spectral density functions occurs at a frequency with a corresponding wavelength close to 4πw which has significance in terms of the meander wavelength-width relationship (Richards, 1976a). This consistency is remarkable considering local differences. In addition, sections in curved reaches tend to be more asymmetric, especially when sited at pools. However, contrary to expectation, channel width is not significantly correlated with asymmetry.  相似文献   

1901-1995年气候变化导致陆地生态系统净吸收碳   总被引：2，自引：0，他引：2  

Yang Xin  Wang Mingxing  Huang Yao 《大气科学进展》2001,18(6):1192-1206

The spatial and temporal variability of land carbon flux over the past one hundred years was investigated based on an empirical model directly calculating soil respiration rate. Our model shows that during 1901-1995, about 44-89 PgC (equals to 0.5, 0.9 PgC/yr respectively) were absorbed by terrestrial biosphere. The simulated net ecosystem productivity (NEP) after the 1930s was close to the estimated value of" missing C sink” from deconvolution analysis. Most of the total carbon sink happened during 1951-1985 with the estimated value of 33-50 PgC. Three major sinks were located in the tropics (10°S-10°N), Northern mid-latitudes (30°-60°N) and Southern subtropics (10°-40°S). During 1940s-mid-1970s, carbon sinks by terrestrial ecosystem increased with time, and decreased after the mid-1970s. These may be due to the ch anging of climate condition, as during the 1940s-1970s, temperature decreased and precipitation increased, while after the mid-1970s, an opposite climate situation occurred with evident increasing in temperature and decreasing in precipitation. Usually, warmer and dryer climate condition is not favor for carbon absorption by biosphere and even induces net carbon release from soil, while cooler and wetter condition may induce more carbon sink. Our model results show that the net carbon flux is particularly dependent on moisture / precipitation effect despite of temperature effect. The changing of climate in the past century may be a possible factor inducing increases in carbon sink in addition to CO2 and N fertilizer.  相似文献   

利用卫星云图作广西强降水短时预报   总被引：6，自引：2，他引：6  

林宗桂  陈冰廉 《广西气象》2005,26(4):1-4

构造天气学意义明确的卫星云图状态函数模型，在对云层进行分类的基础上，定量提取卫星云图参数，通过与云图模板的相似运算寻找短时预报指标。试报结果表明，这种方法对提高强降雨落区的短时预报准确率是可行的。  相似文献   

A PCSWMM/GIS-based water balance model for the Reesor Creek watershed   总被引：1，自引：0，他引：1  

D. Smith  J. Li  D. Banting   《Atmospheric Research》2005,77(1-4):388

This paper presents the results of a study of a watershed experiencing the pressures of land-use change resulting from urban development. The study was undertaken to facilitate an understanding of the water balance of the watershed by developing and implementing watershed procedures that are to be addressed in a watershed plan. There were three components to the research: firstly, observation of the effects of spatially distributed rainfall measurements and their effect on modelling were assessed. Secondly, the model was then calibrated by observing how differing techniques can discretize both the landscape (e.g. land-use and soil type) and incoming precipitation. Finally, a modelling methodology was developed to integrate a Geographic Information System and a hydrologic model (e.g. Storm Water Management Model) in a water balance analysis on a watershed basis. Results show that, under certain conditions, kriging spatially distributed rainfall values can help predict rainfall at ungauged (virtual) sites. Discretization of a watershed was found to affect the differences between measured and generated runoff volumes; however, this can be refined with calibration. It was seen that a strong correlation between measured and predicted rainfall values did not always guarantee a strong relationship between measured and generated runoff Recommendations include the use of a longer time series of rainfall, streamflow and predicted rainfall to observe temporal variations, and the need to assess the differences in modelled rainfall values generated by various surface interpolation methods (e.g. Inverse Distance Weighting and other kriging options) currently available in GIS packages.  相似文献   

Landslides in the Central Coalfield (Cantabrian Mountains, NW Spain): Geomorphological features, conditioning factors and methodological implications in susceptibility assessment   总被引：2，自引：0，他引：2  

María Jos Domínguez-Cuesta  Montserrat Jimnez-Snchez  Edgar Berrezueta 《Geomorphology》2007,89(3-4):358-369

A geomorphological study focussing on slope instability and landslide susceptibility modelling was performed on a 278 km² area in the Nalón River Basin (Central Coalfield, NW Spain). The methodology of the study includes: 1) geomorphological mapping at both 1:5000 and 1:25,000 scales based on air-photo interpretation and field work; 2) Digital Terrain Model (DTM) creation and overlay of geomorphological and DTM layers in a Geographical Information System (GIS); and 3) statistical treatment of variables using SPSS and development of a logistic regression model. A total of 603 mass movements including earth flow and debris flow were inventoried and were classified into two groups according to their size. This study focuses on the first group with small mass movements (10⁰ to 10¹ m in size), which often cause damage to infrastructures and even victims. The detected conditioning factors of these landslides are lithology (soils and colluviums), vegetation (pasture) and topography. DTM analyses show that high instabilities are linked to slopes with NE and SW orientations, curvature values between − 6 and − 0.7, and slope values from 16° to 30°. Bedrock lithology (Carboniferous sandstone and siltstone), presence of Quaternary soils and sediments, vegetation, and the topographical factors were used to develop a landslide susceptibility model using the logistic regression method. Application of “zoom method” allows us to accurately detect small mass movements using a 5-m grid cell data even if geomorphological mapping is done at a 1:25,000 scale.  相似文献   

Identifying linear and non-linear behaviour in reduced complexity modelling output using surrogate data methods     

C.J. Keylock   《Geomorphology》2007,90(3-4):356

Validation of model output is an important issue in the environmental sciences. This is particularly the case for reduced complexity modelling approaches where verification of the underlying equations is often problematic. Hence, methods that go beyond validation based on average values or the histogram of model output, are clearly advantageous. In this paper we show that a validation method based on the serial properties of time–space data, and developed in geomorphology, is a useful alternative but is nevertheless still insensitive to certain asymmetric characteristics of the signal. Hence, use of this method for validation may be enhanced by the adoption of an accompanying test for asymmetry in the model output.  相似文献   

区域可持续发展的一种评价模型:综合协调度——以广东省沿海城市为例   总被引：3，自引：0，他引：3  

熊永柱  夏斌  张美英 《热带地理》2007,27(6):511-515,520

采用层次分析法(AHP)和主成分分析法建立了一种区域可持续发展定量评价的指标体系和综合协调度模型,确定了评价指标体系的权重,并根据广东省沿海14个地市1995年至2004年的统计数据,对其可持续发展综合协调度进行了定量评价。结果表明:(1)广东省沿海区域可持续发展的综合协调度总体上呈现上升趋势,但东中西部分布不均衡,呈现粤中较高东西两翼较低的格局;(2)14个沿海地市中,1995年综合协调度均处于较弱水平(Ⅳ),到2004年,只有深圳、广州的综合协调度超过0.4,达到中等协调水平(Ⅲ),而其它地市仍处于较弱水平(Ⅳ)的综合协调度阶段。  相似文献   

Performance of surface footing on geocell-reinforced soft clay beds   总被引：2，自引：0，他引：2  

Sitharam G. Thallak  Sireesh Saride  Sujit Kumar Dash 《Geotechnical and Geological Engineering》2007,25(5):509-524

This paper presents the results of laboratory model tests carried out to develop an understanding of the behaviour of geocell-reinforced soft clay foundations under circular loading. Natural silty clay was used in this study. The geocells were prepared using biaxial polymer grid. The performance of the reinforced bed is quantified using non-dimensional factors i.e., Bearing capacity improvement factor (I_f) and Percentage reduction in footing settlement (PRS). The test results demonstrate that the geocell mattress redistributes the footing load over a wider area thereby improving the performance of the footing. The load carrying capacity of the clay bed is increased by a factor of up to about 4.5 times that of unreinforced bed. From the pressure-settlement responses, it is observed that the geocell-reinforced foundation bed behaves as a much stiffer system compared to the unreinforced case indicating that a substantial reduction in footing settlement can be achieved by providing geocell reinforcement in the soft clay bed. The maximum reduction in footing settlement obtained with the provision of geocell mattress of optimum size placed close to the footing is around 90%. Further improvement in performance is obtained with provision of an additional planar geogrid layer at the base of the geocell mattress.  相似文献   

Least-squares self-coherency analysis of superconducting gravimeter records in search for the Slichter triplet   总被引：3，自引：0，他引：3  

Spiros D. Pagiatakis  Hui Yin 《Physics of the Earth and Planetary Interiors》2007,160(2):108-123

We develop a new approach for the spectral analysis of the superconducting gravimeter data to search for the spheroidal oscillation ₁S₁ of the Earth solid inner core. The new method, which we call least-squares (LS) self-coherency analysis, is based on the product of the least-squares spectra of segments of the time series under consideration. The statistical foundation of this method is presented in the new least-squares product spectrum theorem that establishes rigorously confidence levels for detecting significant peaks. We apply this approach along with a number of other innovative ideas to a 6-year long gravity series collected at the Canadian Superconducting Gravimeter Installation (CSGI) in Cantley, Canada, by splitting it into 72 statistically independent monthly records. Each monthly record is analysed spectrally and all monthly LS spectra are multiplied to construct the self-coherency spectrum of the 6-year gravity series. The self-coherency spectrum is then used to detect significant peaks in the band 3-7 h at various significant levels with the aim to identify a triplet of periods associated with the rotational/ellipsoidal splitting of ₁S₁ (Slichter triplet). From all the Slichter periods predicted by various researchers so far, Smylie's triplet appears to be the most supported one, albeit very weakly, both, before and after the atmospheric pressure effect is removed from the series. Using the viscous splitting law [Smylie, D.E., 1992. The inner core translational triplet and the density near Earth's center. Science 255, 1678-1682] as guide, we can also see one interesting and statistically significant triplet with periods A = {4.261 h, 4.516 h, 4.872 h}, which changes slightly to A′ = {4.269 h, 4.516 h, 4.889 h} after the atmospheric pressure correction is applied to the gravity series.  相似文献