地震序列障碍体模型的数值模拟试验研究     

李宇彤  焦明若 《内陆地震》2006,20(1):25-32

运用岩石破裂过程分析RFPA2D系统,研究了断层上含非均匀性障碍体对地震序列类型的影响。通过对断层障碍体不同均质度系数m=1.1、m=1.5、m=6.0这3个样本进行破裂过程的模拟,发现均质度不同会产生不同地震序列类型,这些序列类型主要是前震主震余震型、主震型和震群型。此外,对3种不同均质度的障碍体的岩石样本破裂过程的模拟表明,岩石介质的非均匀性不但对岩样宏观强度和宏观变形非线性行为有显著的影响,而且对试样破裂模式也有显著的影响。  相似文献   

细观非均匀性对岩石破裂过程和微震序列类型影响的数值试验研究   总被引：15，自引：1，他引：15       下载免费PDF全文

焦明若  唐春安  张国民  石耀霖  侯万凯 《地球物理学报》2003,46(5):659-666

运用岩石破裂过程分析RFPA2D系统，研究了岩石介质细观非均匀性对宏观力学行为的影响和微震序列特征. 通过对不同均质度系数m=1.1，1.5，2，3，5的5个样本进行破裂过程的模拟，发现均质度不同会产生不同地震序列类型，主要有：前震-主震-余震型、主震型和震群型. 此外，对5种不同均质度系数的岩石样本破裂过程的模拟表明，岩石介质的非均匀性不仅对岩样宏观强度和宏观变形非线性行为有显著的影响，而且也显著地影响试样破裂模式. 随着均质度系数的提高，主破裂呈现脆断模式. 同时介质的细观结构随机性，也对试样宏观破裂模式产生重要影响.  相似文献   

Determination of Area-Averaged Sensible Heat Fluxes with a Large Aperture Scintillometer over a Heterogeneous Surface – Flevoland Field Experiment     

W. M. L. Meijninger  O. K. Hartogensis  W. Kohsiek  J. C. B. Hoedjes  R. M. Zuurbier  H. A. R. De Bruin 《Boundary-Layer Meteorology》2002,105(1):37-62

To test the applicability of the scintillation method over a heterogeneous area an experiment was carried out in the summer of 1998 in Flevoland (The Netherlands). In the patchy area only four crops were grown namely sugar beet, potatoes, wheat and onions. From eddy covariance measurements it was found that the heterogeneity was mainly caused by differences in thermal properties. No variations in the aerodynamics roughness length were observed. Two large aperture scintillometers were installed at a height of 11.6 and 20.4 m. A good resemblance was found between the sensible heat fluxes derived from both LAS instruments and the area-averaged fluxes obtained from the in-situ eddy covariance measurements. The slight underestimation of the lower LAS could be assessed using a blending height model and an analytical footprint model. The results also indicated that when scintillometer measurements are made below the blending height the violation to Monin–Obukhov Similarity Theory is small and that reasonable fluxes can be obtained from path-averaged structure parameters.  相似文献   

Effect of plant species on shrub fertile island at an oasis–desert ecotone in the South Junggar Basin, China     

J. Li  C. Zhao  H. Zhu  Y. Li  F. Wang   《Journal of Arid Environments》2007,71(4):350-361

Shrub fertile islands are a common feature in arid ecosystems. To examine the effect of plant species on the spatial patterns of soil chemical and physical properties surrounding individual shrubs, two deciduous shrub species with different morphologies (Tamarix spp. and Haloxylon ammodendron Bge.) were studied at an oasis–desert ecotone in South Junggar Basin. Soil samples were collected under the shrub crown (canopy), at the vertically projected limit of shrub crown margin (periphery), and in the space between shrub crowns (interspace) at two depths, 0–10 and 10–20 cm, to analyze their physical and chemical properties. The results show that the fertile islands of Tamarix spp. are enriched with more soil nutrients (significantly higher, P<0.05; soil organic matter (SOM); total nitrogen (TN) and available nitrogen (AN); to a deeper depth (>20 cm) and in a larger area (beyond the canopied area) compared to that of H. ammodendron (significantly higher, P<0.05, soil nutrients detected only for AN; <20 cm in depth; smaller than the canopied area). Soil texture patterns surrounding the shrubs of the two species are even more different, with more coarse particles under the Tamarix spp. canopies compared to the interspace between shrubs but fewer under the H. ammodendron canopies compared to the interspaces. These variations are attributed to the difference in morphology of the two studied species: the Y-shaped crowns of H. ammodendron are less capable of capturing and maintaining litter under them than the hemispheroidal crowns of Tamarix spp., which leads to the less well developed fertile islands surrounding H. ammodendron shrubs.  相似文献   

Reducing geological uncertainty by conditioning on boreholes: the coupled Markov chain approach     

Amro M. M. Elfeki  F. M. Dekking 《Hydrogeology Journal》2007,15(8):1439-1455

The CMC (coupled Markov chain) model, which is based on the extension of Markov chains in two-dimensions, is used in the reduction of uncertainty in geological structures when conditioned (i.e., honours the data and their location) on a number of boreholes. The model has been applied to an unconsolidated aquifer deposit located in the central Rhine-Meuse delta (the Gorkum study area) in the Netherlands. A comparison is also made between the CMC and the SIS (sequential indicator simulation) model, which is based on Kriging and co-Kriging theories on the same deposit. The results show the potential applicability of the CMC model in reducing the uncertainty in geological configurations when a sufficient number of boreholes is available. Reproduction of the global geological features requires relatively few boreholes (in this case study, nine boreholes with 30-m spacing over a distance of 240 m). However, reproduction of the proportion of each state requires a relatively large number of boreholes (in this case study 31 boreholes with 8-m spacing over a distance of 240 m). It has been shown that variograms can be deceptive in modeling the spatial pattern and that they reflect only part of the complete spatial structure in the field. The use of transition probabilities via the CMC model provides a better alternative approach, because it uses multiple point information. Amro M. M. Elfeki on leave from Department of Irrigation and Hydraulics, Faculty of Engineering, Mansoura University, Mansoura, Egypt  相似文献   

Tigers, trees and Tharu: An analysis of community forestry in the buffer zone of the Royal Chitwan National Park, Nepal   总被引：1，自引：0，他引：1  

Samantha Jones 《Geoforum》2007,38(3):558-575

In the buffer zone of the Royal Chitwan National Park (RCNP), community forests represent a key land use to meet the objectives of the buffer zone concept. This article examines three diverse community forests surrounding the national park and explores how national policy has been mediated by emerging community forestry institutions to create different levels of resource access and benefit distribution both within and between local user groups. Mindful of recent critiques of community-based conservation, the analysis gives considerable attention to the dynamics of power relations and inequality. The extent to which property rights have been transferred to the local level is evaluated and to whom power has been devolved in the process is assessed. The distribution of benefits arising from community forestry is critically examined. It seems that the current system for community forestry creates sufficient incentives for local cooperation due to the potential for increased access to important resources and a high perception of ownership of community forests among the communities. However, emerging institutions vary in the extent to which they reproduce favourable resource access conditions for elites and benefit distribution does seem to be skewed in favour of the wealthy and higher castes, even where management practices on the surface appear fair. National policy creates sufficient but not necessary conditions for achieving downward accountability, transparency and fairness. Greater attention to these issues is needed for buffer zone community forestry to better serve the poor and marginalised populations within user groups.  相似文献   

Heterogeneous Features of Temporal and Spatial Variation of Earthquake Occurrence in Process of Earthquake Preparation     

Huang Yun  Gao Xu  Xie Huazhang 《中国地震研究》2001,15(1):47-56

By applying the GL-value, a parameter describing the heterogeneities in temporal and spatial distribution of moderate and small earthquakes prior to strong earthquakes, the following problems have been studied in the present paper: a systematic investigations have been made on the features of spatial distribution and temporal variation of the high value anomalies ( GL ≥1.0) prior to 28 moderately strong earthquakes with Ms ≥5.0 in the North China region; a systematic study has been made on the reasonability of the lower limit of magnitude, the time window and the space window for calculations at various seismicity levels in this region; the parameters taken in the calculation have been optimized and modified; the anomalous variations of GL-value prior to various moderately strong earthquakes in North China region have been investigated and followed, using the total time-space scanning method. The results of the study have shown that for 82 % of the moderately strong earthquakes in the North China region, obvious anomalous region with high GL-values appears near the future epicenter about 1 ～ 3.5 years before the earthquakes. The earthquakes usually occur in the marginal area of the anomalous zone or near it. Temporal variations of the GL-values in the anomalous zone show that the duration of anomalous ranges between 3 ～ 25 months with a predominant interval of 5 ～ 19 months, into which about 70% the total anomalies fall. The predominant interval of earthquake occurrences is 0 ～ 14 months after ending of the anomaly, into which about 83 % of the total anomalies fall. Based on these results the GL-value method is considered to be a rather effective prediction method for moderately strong earthquakes in the North China region.  相似文献   

Mapping the heterogeneity of natural and semi-natural landscapes     

《International Journal of Applied Earth Observation and Geoinformation》2014

Natural and semi-natural landscape cover is heterogeneous. Ideally, mapping land cover requires an approach that represents both gradients and land covers spatiotemporal variability. These aspects can be visualized and depicted by applying a new spatio-temporal analysis based Landscape Heterogeneity Mapping (LaHMa) method to natural and semi-natural landscapes. Using MODIS NDVI 16-day imagery (February 2000–July 2009) for Crete, a 65-cluster image was selected from ISODATA classification results using the separability values of the divergence statistics. The 65 clusters appropriately generalize the spatial and temporal variability in land cover. Using classified outputs from 10 to 65 clusters, the frequency of pixels identified as boundaries of homogeneous land cover classes was translated into the form of a landscape heterogeneity map, which was then validated using field data. The results show that the heterogeneity map had moderate correlation (R² = 0.60 and 0.63 in two transects) with the sum of differences between neighbouring transect pixels in all land cover components. In general, the study found this new approach (LaHMa) to be suitable for mapping landscape heterogeneity in the natural and semi-natural landscape of Crete, Greece. The new method appears to be of potential use for informing gradient analyses in landscape ecological studies.  相似文献   

Parameter sensitivity of a hydrocarbon biodegradation model under uncertainty of permeability     

Aly I. El-Kadi 《Hydrogeology Journal》2007,15(2):339-350

The effects of permeability variability on uncertainty of the results of a hydrocarbon biodegradation model are addressed. The model includes saturated and unsaturated flow, multi-species transport, heat transport, and bacterial-growth processes. A stochastic approach was used in the uncertainty analysis. Sensitivity analyses were conducted, taking into consideration the effects of heterogeneity. The Monte Carlo method was used, with permeability as the input stochastic variable. Results showed that uncertainty increases with time. This can lead to difficulties regarding cleanup decision making such as predicting the timeframe to reach an aquifer cleanup goal. It was not possible to replace the heterogeneous system with a homogeneous one through the use of effective parameters that preserve an equivalent behavior of the two systems. Effective permeability is space and time dependent and also depends on values of bioactivity parameters. The study also emphasized the importance of accurately measuring certain bacterial parameters, namely, maximum substrate uptake rate for degradation and cell yield coefficient. Uncertainties regarding nutrient and oxygen uptake and saturation parameters were less important for the current application.

Aly I. El-KadiEmail:

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Random field modeling of the void phase of soils     

《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2013,7(1):57-68

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