共查询到20条相似文献，搜索用时 15 毫秒
1.
Alan Yong Susan E. Hough Michael J. Abrams Christopher J. Wills 《Journal of Earth System Science》2008,117(2):797
Estimation of the degree of local seismic wave amplification (site effects) requires precise information about the local site conditions. In many regions of the world, local geologic information is either sparse or is not readily available. Because of this, seismic hazard maps for countries such as Mozambique, Pakistan and Turkey are developed without consideration of site factors and, therefore, do not provide a complete assessment of future hazards. Where local geologic information is available, details on the traditional maps often lack the precision (better than 1:10,000 scale) or the level of information required for modern seismic microzonation requirements. We use high-resolution (1:50,000) satellite imagery and newly developed image analysis methods to begin addressing this problem. Our imagery, consisting of optical data and digital elevation models (DEMs), is recorded from the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) sensor system. We apply a semi-automated, object-oriented, multi-resolution feature segmentation method to identify and extract local terrain features. Then we classify the terrain types into mountain, piedmont and basin units using geomorphometry (topographic slope) as our parameter. Next, on the basis of the site classification schemes from the Wills and Silva (1998) study and the Wills et al (2000) and Wills and Clahan (2006) maps of California, we assign the local terrain units with V s 30 (the average seismic shear-wave velocity through the upper 30m of the subsurface) ranges for selected regions in Mozambique, Pakistan and Turkey. We find that the applicability of our site class assignments in each region is a good first-approximation for quantifying local site conditions and that additional work, such as the verification of the terrain’s compositional rigidity, is needed. 相似文献
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Tianwu Ma Yonggang Chen You Hua Zhende Chen Xiaoyin Chen Chengzhi Lin Chunju Yang 《Earth Science Informatics》2017,10(1):29-39
The DEM generalization is the foundation of expressing and analyzing the terrain and the basis of multi-scale observation. Meanwhile, it is also the core of building the multi-scale geographic database. This paper would like to propose a new algorithm using profile simplification in four directions(4-DP). This algorithm is composed of two parts, namely extraction of terrain feature points in local window as well as in global profile line and reconstruction of DEMs. The paper used the 5 m resolution DEM of the Suide in Loess Plateau of China as the original data. In the experiment, this paper has achieved the generalized DEM with 5 m and 25 m resolution by removed small details and computed out the optimal threshold. In contrast to the classic algorithms, VIP and Aggregate, based on three evaluation methods. The results show that this method is able to retain the main geographical information effectively in terrain surface. 相似文献
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在油气田开发过程中,微震监测是获得水力压裂引起裂缝分布的一种较为有效的方法。微震的定位成像与裂缝解释需要利用有效微震信号位置,而微震信号具有低信噪比的特点,传统信号拾取方法无法有效实现较低信噪比条件下初至时刻的准确拾取。本文提出一种基于时频谱熵的初至拾取新方法,该方法首先通过S变换获取含噪信号的时频谱;然后对谱内各个采样点沿频率方向进行分帧操作,并计算每帧频段内的近似负熵值,以最小近似负熵值作为该谱点的负熵值;最后沿时间方向比较各谱点的负熵值,最小值对应的时刻即为初至时刻。本文利用不同信噪比的合成地震数据对该方法进行效果验证,并与长短时窗能量比（STA/LTA）法进行拾取结果对比,结果表明：信噪比在-5 dB时,两种方法拾取效果都很好;信噪比在-10 dB时,时频谱熵法拾取效果更好。时频谱熵法更适合低信噪比情况下的信号初至拾取。 相似文献
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坍塌是山岭隧道施工过程中主要灾害之一。由于影响坍塌的因素众多,且各因素所占的权重差异较大,甚至有些因素是不必要或冗余的。目前常用的评价方法不但未对这些不必要或冗余的因素进行筛选,而且权重的确定过于依赖专家经验和主观赋值,导致风险评价结果精度低、可靠性差。基于此,应用粗糙集理论在数据挖掘、指标筛选和重要性计算方面的优势,将山岭隧道坍塌风险评价构建为粗糙集的决策信息表。但工程试验发现,基于传统依赖度的属性约简及权重计算不能满足要求,存在计算权重为0或约简结果过多,无法取舍的问题。针对以上问题,提出了一种基于条件信息熵的计算方法,该方法将条件信息熵引入到属性重要度和权重的定义中,同时以最重要的条件属性为起点,逐步增添属性,实现属性约简。所建立的方法既能从大量影响因素中,提取出主要影响因素,剔除相对冗余或不重要的因素;同时又能计算得到各因素的客观权重。最后结合模糊综合评价法,建立了基于粗糙集条件信息熵的山岭隧道坍塌风险评价模型,并成功应用于秀村隧道中,表明该模型可靠、实用,为山岭隧道坍塌风险评价提供一条新的研究思路。 相似文献
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Rolland Andrade 《Journal of the Geological Society of India》2011,78(4):337-344
Electrical Resistivity Tomography (ERT) has been used in association with several geohydrological, geotechnical and geophysical
methods in resolving several site specific problems in hydrological science. Advancement in the field of computers and automation
in the field of electronics has jointly resulted in the development of this geophysical innovation which has wide application
in groundwater, environmental and engineering problems including monitoring of vadose zone water movement, steam injection
etc. In this paper application of ERT in association with geohydrological and other exploration methods in resolving groundwater
sustainability problem of a micro-watershed area in semi arid granite terrain is presented as three independent cases. In
a hard rock terrain the probability of complexities in understanding the sub-surface lithology and its corresponding hydrological
parameters are more. Hence appropriate resistivity survey configuration and suitable inversion of acquired data in congregation
with other geo-scientific investigations were carried out to understand the site specific problem. The study demonstrated
as 3 independent cases shows the usefulness of the ERT method in hydrological investigations, which is economic, efficient
and less time consuming in comparison to the other exploration methods. 相似文献
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Practical Calculation of Non-Gaussian Multivariate Moments in Spatiotemporal Bayesian Maximum Entropy Analysis 总被引：1，自引：0，他引：1
During the past decade, the Bayesian maximum entropy (BME) approach has been used with considerable success in a variety of geostatistical applications, including the spatiotemporal analysis and estimation of multivariate distributions. In this work, we investigate methods for calculating the space/time moments of such distributions that occur in BME mapping applications, and we propose general expressions for non-Gaussian model densities based on Gaussian averages. Two explicit approximations for the covariance are derived, one based on leading-order perturbation analysis and the other on the diagrammatic method. The leading-order estimator is accurate only for weakly non-Gaussian densities. The diagrammatic estimator includes higher-order terms and is accurate for larger non-Gaussian deviations. We also formulate general expressions for Monte Carlo moment calculations including precision estimates. A numerical algorithm based on importance sampling is developed, which is computationally efficient for multivariate probability densities with a large number of points in space/time. We also investigate the BME moment problem, which consists in determining the general knowledge-based BME density from experimental measurements. In the case of multivariate densities, this problem requires solving a system of nonlinear integral equations. We refomulate the system of equations as an optimization problem, which we then solve numerically for a symmetric univariate pdf. Finally, we discuss theoretical and numerical issues related to multivariate BME solutions. 相似文献
8.
Xavier Emery 《Mathematical Geosciences》2008,40(6):671-688
An important aspect in mineral resource evaluation is the reduction of variance when post-processing the grade distributions
defined on the support (volume) of the available data into distributions defined on the support of the proposed selective
mining units. Although the volume-variance relationship is well understood for the estimation of global grade distributions,
it is still an unsolved issue for local estimation studies based on non-parametric geostatistical methods, such as indicator
kriging, for which the support correction is not inherent to the method. To clarify this relationship, the local change of
support problem is examined in the scope of two parametric models (multi-Gaussian and discrete Gaussian models). It is shown
that the variance reduction factor between point and block-support local distributions depends on the block being considered
and is less than the global variance reduction factor. As a consequence, post-processing the local point-support grade distributions
on the basis of the latter systematically understates the importance of the change of support at the local scale and makes
selective mining appear more economically attractive than it really is. In the light of these results, a methodology is proposed
to post-process the local point-support distributions obtained via non-parametric (indicator) methods into block-support distributions.
An application to simulated data indicates that this methodology provides an accurate estimation at the block support when
dealing with diffusion-type random fields. 相似文献
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复杂地形下高密度激电法2.5维有限单元法数值模拟 总被引：1，自引：0，他引：1
目前三维有限元模拟计算量大,计算效率低,对计算机要求较高,2.5维模拟是三维问题的简化,较好地克服了上述问题。在高密度激电法模拟中,模拟的点数一般较大,要求程序计算效率高,因此对高密度激电法2.5维模拟研究是必要的。首先给出了2.5维稳定电流场的边值问题及对应的变分问题;为了能更好模拟复杂地形对极化率异常的影响,采用三角形网格,有利于模拟复杂地形又有利于将其应用于反演计算。推导了基于连续电性介质的2.5维稳定电流场的有限元法,利用等效电阻率法,编制了2.5维高密度激电法有限元模拟程序,计算了水平地形及起伏地形下的极化率异常模型,并验证了方法的可行性,分析得出了山谷地形比山脊地形对极化率观测的影响大的结果。 相似文献
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传统方法在选取潜在滑裂面关键点时,未综合考量剪切滑裂点、受拉滑裂点对搜索过程的影响程度,导致搜索过程易陷入局部最优,从而丢失其他同等级搜索数据。针对这一问题,本研究设计了基于GA-Sarma算法的边坡最不利滑裂面搜索方法。该方法通过计算边坡稳定性系数的实际值提取边坡潜在滑裂面,然后根据剪切滑裂点、受拉滑裂点的特性,选取潜在滑裂面关键点。进而,基于GA-Sarma算法建立目标函数和适应度函数,在考虑变异的前提下搜索边坡的最不利滑裂面。实验测试区域中包含3处最不利滑裂面、5处刚刚形成且危险程度偏低的滑裂面、14处潜在滑裂面。测试结果表明：在20轮测试中,本文方法与两组传统方法搜索到的最不利滑裂面个数平均值分别为3处、1.4处以及0.8处,从而验证了GA-Sarma算法强化了边坡最不利滑裂面搜索效果。该方法可为边坡支护、加固及改造等地质工作提供更加可靠的技术支持。 相似文献
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冰下地形与冰川体积的估算对冰川水资源研究具有重要意义.以萨吾尔山木斯岛冰川为研究对象,利用Landsat影像数据、探地雷达(ground penetrating radar,简称GPR)冰川厚度数据以及差分GPS数据,分析模拟了萨吾尔山木斯岛冰川横纵剖面的厚度分布特征,采用多种插值方法比较分析,得到木斯岛冰川冰舌区的厚度分布图,初步估算了该冰川的冰储量.结合数字高程模型数据及冰川厚度分布图,绘制了木斯岛冰川冰舌区冰床地形图.研究表明,两个横剖面的冰川槽谷形态存在较大的差异.横剖面B1-B2有典型的“U”型地形发育,冰川厚度可达116.4 m;C1-C2横剖面底部地形比较平缓,冰川厚度分布较均匀,平均在70~90 m.纵测线A1-A2冰下地形成阶梯状分布,纵剖面冰体平均厚度约为80.89 m,最大冰体厚度为122.67 m.木斯岛冰川的冰床地形图与该冰川的冰厚度等值线图形成明显对比.在海拔3 240 m和3 280 m处存在明显的冰斗地形地貌.初步估算木斯岛冰川冰舌区的平均厚度和冰储量分别为60.5 m和0.195 km3.与传统计算冰储量的方法相比,利用GPR测量得到的冰川厚度数据来插值计算冰储量的方法,具有更高的准确性. 相似文献
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A Bayesian/maximum-entropy view to the spatial estimation problem 总被引：12，自引：0，他引：12
George Christakos 《Mathematical Geology》1990,22(7):763-777
The purpose of this paper is to stress the importance of a Bayesian/maximum-entropy view toward the spatial estimation problem. According to this view, the estimation equations emerge through a process that balances two requirements: High prior information about the spatial variability and high posterior probability about the estimated map. The first requirement uses a variety of sources of prior information and involves the maximization of an entropy function. The second requirement leads to the maximization of a so-called Bayes function. Certain fundamental results and attractive features of the proposed approach in the context of the random field theory are discussed, and a systematic spatial estimation scheme is presented. The latter satisfies a variety of useful properties beyond those implied by the traditional stochastic estimation methods. 相似文献
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Adding Local Accuracy to Direct Sequential Simulation 总被引：3，自引：0，他引：3
Jef Caers 《Mathematical Geology》2000,32(7):815-850
Geostatistical simulations are globally accurate in the sense that they reproduce global statistics such as variograms and histograms. Kriging is locally accurate in the minimum local error variance sense. Building on the concept of direct sequential simulation, we propose a fast simulation method that can share these opposing objectives. It is shown that the multiple-point entropy of the resulting simulation is related to the univariate entropy of the local conditional distributions used to draw simulated values. Adding local accuracy to conditional simulations does not detract much from variogram reproduction and can be used to increase multiple-point entropy. The methods developed are illustrated using a case study. 相似文献
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局部结构熵算法在地震数据不连续性检测中的应用 总被引：2，自引：0，他引：2
自从相干地震数据体概念被提出以来,许多学者提出了不同的基于相干性检测地质结构不连续性的算法。例如,基于特征结构的相干算法,局部结构熵算法以及第二与第一特征值比值算法等。本文基于小波变换具有多尺度多分辨率分析的优点,提出了在特定的小波变换分频瞬时属性上,利用局部结构熵算法来检测地震数据的局部不连续性。实际地震资料检测结果表明,基于分频瞬时相位的局部结构熵算法更能有效地检测到地震数据的细微变化,对于油气藏的精细刻画有重要意义。 相似文献
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在区域地质调查中,地质剖面测制是一项必要的工作,而传统的导线法限制因素较多,质量和效率有待提高。在导线法的基础上,基于野外实践经验,提出了一种地质剖面测制新方法,即点坐标法。该方法的要点有:利用GPS获得地形控制点,以及分层、采样、产状、照相等位置的三维点坐标;构建一套函数公式,根据各点的三维空间坐标值,可计算获得点间平距、高差、方位角、坡度角等参数,从而投影绘制地质剖面图。该方法的主要优点有:不再需要测绳,可从人工测量记录转变为自动测量记录,实现了测量数据的数字化;避免了导线终点与实际终点不重合的情况;每一个分层点都有GPS坐标,便于野外复查。结合点坐标法测制地质剖面的实例证明,点坐标法较之导线法有多快好省的优点,值得在实际应用中广泛使用。 相似文献
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在地形起伏较大的地区获取遥感影像时,由于地形效应的存在,阴影的产生几乎是不可避免的。为此,对多光谱图像进行波段比值处理,减弱或者消除地形阴影的影响,提高遥感影像的识别与分类精度,并对处理后的图像进行质量评价,为选择最佳处理方法提供参考。结合数字高程模型(DEM)对山区遥感图像进行分区,对分区结果进行各种波段比值运算,消除地形阴影;以信息熵作为质量评价指标,对比值处理消除地形阴影后的结果进行定量分析,研究处理结果与所选比值处理方法之间的联系。结果表明,波段比值处理可以减弱或者消除地形阴影的影响,与单波段比值处理和线性波段比值处理相比,非线性波段比值处理后图像的信息熵增强最大。 相似文献
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地震数据本质上是非平稳的,如何解决复杂非平稳地震波场的数据缺失问题是地震勘探数据处理的重要环节之一。预测滤波器在地震数据处理和分析中具有重要的作用,该技术可以有效地解决地震数据缺失问题,但传统的平稳预测滤波方法无法很好地适应地震数据的非平稳特征;因此,开发高效的复杂地震波场自适应预测插值方法具有重要的工业价值。本文将预测滤波器加入"流处理"的概念,滤波器系数随着地震数据的变化同时更新,此计算过程仅需矢量点积运算,能够提高计算效率并降低内存空间;并以此为基础开发基于流预测滤波的地震数据插值方法。利用多次波的动力学信息,通过互相关技术构建虚拟一次波,有效地解决了缺失数据位置滤波系数估计不准的问题,为插值过程提供了更为合理的滤波器估计,更好地解决了非平稳地震数据的重建问题。对Sigsbee 2B模型和实际数据的测试结果表明,该方法可以合理地针对复杂地震信息完成缺失数据的重建。 相似文献