半地堑反转构造的砂箱实验模拟   总被引：8，自引：1，他引：8  

周建勋 《地球物理学进展》1999,14(3):47-53

设计了两组半地堑反转垢理想砂箱实验模型。实验结果表明，边界条件对半地堑反转构造形成特征有着十分明显的影响。刚性边界条件下，沿着边界断层可以产生一定的反转逆冲现象，反转逆冲的程度与边界断层的倾角大小有关，倾角越缓反转逆冲现象越显著，而在自由边界条件下，边界断层均无反转逆冲现象，只是发生倾角变陡现象。沿半地堑边界断层的反转逆冲作用十分有限，反转逆冲主要通过新生低角度逆冲断层得以实现，地堑内部断层通常不  相似文献   

科尔沁沙地土壤水分动态分析及其概率密度函数模拟   总被引：2，自引：0，他引：2       下载免费PDF全文

姚淑霞  张铜会  赵传成 《水科学进展》2013,24(1):62-72

基于Laio土壤水分动态随机模型(Laio模型),利用2006-2010年5~9月土壤水分连续监测数据及日降水资料,分析科尔沁沙地固定沙丘和沙质草地生长季根系层土壤水分动态及其与降水格局的关系,研究点尺度土壤水分概率密度函数,并对Laio模型涉及的13个参数进行了敏感性分析。结果表明:① 研究区年降水的季节分配极不均匀,主要集中在4~10月的生长季,占全年降水量的93%;0~5 mm降水事件占全年降水事件的73%,但其降水量只占全年降水量的25%;降水间隔期以0~10 d为主,占全年无降水期的38%,其频数最高,占全年间隔期频数的87%。② 固定沙丘和沙质草地根系层厚度分别为0~100 cm和0~70 cm,沙质草地根系层土壤水分显著高于固定沙丘;两类沙地7月份的土壤水分都显著高于生长季其他月份。③ 两类沙地生长季根系层土壤水分均服从正态分布;通过Laio模型得到了两类沙地生长季根系层土壤水分概率密度函数p(s),其峰值及峰值出现的位置和峰的阔度均与观测结果很接近,说明Laio模型能对科尔沁沙地土壤水分概率密度函数进行较好的模拟。④ Laio模型涉及的13个参数中,对p(s)最为敏感的参数是降水频率λ、平均降水量α、最大蒸散量E_max、水分胁迫点s*和凋萎系数s_w,主要影响p(s)曲线的峰值。  相似文献   

三维地质建模软件发展现状及问题探讨   总被引：5，自引：0，他引：5       下载免费PDF全文

李青元  张丽云  魏占营 《江苏地质》2013,37(4):554-561

分析了三维地质建模软件可以明显地提高工作效率与工程质量,建立勘探区的三维地质模型,检查原始数据的正确性,通过各种“虚拟切割”手段检查各种地质要素间的相互关系。探讨了三维地质建模软件开发中所存在的几个问题,包括软件开发团队应适时转为公司机制,审慎选择开源工具,三维地质建模的三维模型数据标准,在勘探规范中增加三维地质建模要求,二、三维联动编辑,选准产品的用户群的与盈利模式等。  相似文献   

一次大雪天气过程的多普勒雷达特征分析   总被引：7，自引：3，他引：7  

东高红  张志茹  李胜山  贾惠珍 《气象》2007,33(7):75-81

利用常规天气资料、新一代多普勒天气雷达资料和改善的EVAD技术,从影响系统、多普勒雷达回波特征及大气动力学角度,详细分析了2006年2月6日出现在华北地区的大雪天气过程。结果表明：500hPa高空槽、850hPa“人”字型切变及地面气旋相配置是这次大雪天气过程的主要影响系统。在雷达有效探测范围内,随着0.7~1.1km高度上中尺度逆切变的出现和4.8km高度上西南急流的建立并向低层扩展,风场辐合明显加强,辐合层加厚,从而为强降雪的出现和维持提供了有利条件,且中尺度逆切变和西南急流存在的时间与强降雪出现及维持的时间有很好的对应。另外冷锋过境时风场辐合再次加强使得较强降雪继续维持。同时用改善的E-VAD技术计算了降雪不同阶段的大气平均散度和平均垂直速度。结果表明：中尺度逆切变系统和冷锋的出现均对应着明显的辐合和上升,辐合和上升又促使强降雪出现和维持,因而从大气动力学角度进一步证实了中尺度逆切变和冷锋的存在及其与强降雪的对应关系。  相似文献   

基于神经网络方法获得最优化月球内部结构模型     

廖彬彬  徐建桥  陈晓东  孙和平  周江存 《地球物理学报》2022,65(3):939-951

由于观测手段有限,目前对月球内部结构的认识还存在很大的不确定性,至今仍没有一个被广泛认可的内部结构模型,且现有对月球内部结构模型的研究几乎很少关注观测值对观测精度的影响.本研究采用混合密度神经网络方法得到了月球内部结构模型的后验概率密度分布,获得了平均月球内部结构模型(Mean模型)、最大后验概率对应的月球内部结构模型...  相似文献   

地震波数值模拟的非规则网格PML吸收边界   总被引：14，自引：4，他引：10       下载免费PDF全文

徐义  张剑锋 《地球物理学报》2008,51(5):1520-1526

以格子法为基础,以声波方程为例研究非规则网格PML(Perfectly Matched Layer)方法.本方法的核心是建立局部坐标系下的分裂方程和基于积分近似的微分方程弱形式.该非规则网格模拟方法允许在计算域内设置任意形状的人工边界.对于二维半空间问题,与采用矩形人工边界相比,采用半圆形人工边界可减少计算量20%以上.采用光滑的曲边界,不仅可减少计算区域,还可避免常规的PML吸收边界在吸收带角点区域的特殊处理.本方法事先计算和存储边界单元的局部几何参数,在计算的每一时间步查表调用这些参数,与常规的直边界PML方法相比,不增加任何计算量.  相似文献   

Incremental growth of normal faults: Insights from a laser-equipped analog experiment     

Alo Schlagenhauf  Isabelle Manighetti  Jacques Malavieille  Stphane Dominguez 《Earth and Planetary Science Letters》2008,273(3-4):299-311

We conducted a laser-equipped analog experiment aimed at quasi-continuously monitoring the growth of a dense population of normal faults in homogeneous conditions. To further understand the way geological faults progressively gain in slip and length as they accumulate more strain, we measured with great precision the incremental slip and length changes that the analog faults sustain as they grow. These measurements show that the analog faults share common features with the natural ones. In particular, during their growth, the faults develop and maintain cumulative slip profiles that are generally triangular and asymmetric. The growth takes place through two distinct phases: an initial, short period of rapid lateral lengthening, followed by a longer phase of slip accumulation with little or no lengthening. The incremental slip is found to be highly variable in both space (along the faults) and time, resulting in variable slip rates. In particular, ‘short- and long-term’ slip rates are markedly different. We also find that slip measurements at local points on fault traces do not contain clear information on the slip increment repeat mode. Finally, while the fault growth process is highly heterogeneous when considered at the scale of a few slip events, it appears homogeneous and self-similar at longer time scales which integrate many slip increments. This is likely to be the result of a feedback between stress heterogeneities and slip development. The long-term scale homogeneity also implies that the long-term faulting process is primarily insensitive to the short-term heterogeneities that are rapidly smoothed or redistributed. We propose a new conceptual scenario of fault growth that integrates the above observations and we suggest that faults grow in a bimodal way as a result of a self-driven and self-sustaining process.  相似文献   

Hydrogeochemistry and strontium isotopes in the Arno River Basin (Tuscany, Italy): Constraints on natural controls by statistical modeling   总被引：2，自引：0，他引：2  

B. Nisi  A. Buccianti  O. Vaselli  G. Perini  F. Tassi  A. Minissale  G. Montegrossi 《Journal of Hydrology》2008,360(1-4):166-183

In this paper the chemistry of major and trace elements and, for the first time, strontium isotopic ratios measured in running waters from the Arno River Basin (Tuscany, central-northern Italy) and thermal springs discharging in the same hydrographic system are presented and discussed. Classical graphical methods (e.g. mixing diagrams) have here been improved to identify, in a correct statistical sample space, extreme chemical compositions attributable to the action of geochemical processes and/or inherited from specific lithologies (namely contributions or components 1, 2 and 3) to be used in inverse modeling procedures, due to the absence of clear end-members. A linear least squares problem, with non-negativity constraints and distances, as required for compositional data (convex linear mixing) was solved by considering the contribution of the most discriminant variables given by the ⁸⁷Sr/⁸⁶Sr isotopic ratios and the concentration of Ca²⁺, Mg²⁺, Sr and Rb. Following such approach, it can be assumed (p < 0.05) that component 1, characterized by a Ca²⁺(Mg²⁺)– radiogenic-rich (⁸⁷Sr/⁸⁶Sr = 0.71274; Rb/Sr = 0.039), represents a dominant feature at basin scale, with a weight ranging from 69% to 100%. Much lower percentages are related to component 2, represented by a Ca²⁺(Mg²⁺)– facies with intermediate ⁸⁷Sr/⁸⁶Sr (0.70874) and low Rb/Sr (2.8 × 10⁻⁴) ratios and component 3, identified by Ca²⁺– facies with less radiogenic ⁸⁷Sr/⁸⁶Sr (0.70827) and low Mg²⁺/Ca²⁺ (0.011) ratios. These components are mainly dominated by the dissolution of evaporitic rocks and/or mixing with thermal waters in the southern part of the Arno River Basin and by dissolution of the carbonatic fraction, kinetically favored with respect to that of the silicatic minerals, in the upper reaches of the main course and its tributaries, respectively.  相似文献   

An empirical model of event scale cohesive bank profile evolution     

Jim Pizzuto 《地球表面变化过程与地形》2009,34(9):1234-1244

The highly stochastic nature of riverbank erosion has driven the need for spatially explicit empirical models. Detailed bank profile surveys along a meander bend of the Brandywine Creek in Pennsylvania, USA, before and after 28 high flow events over a 2·5 year period are used to develop an empirical model of cohesive bank profile erosion. Two hundred and thirty‐six bank erosion observations are classified as hydraulic erosion or subaerial erosion. Threshold conditions required to initiate bank erosion cannot be defined based on field measurements. Using the near‐bank velocity and the number of freeze–thaw cycles as predictors, regression equations are derived for hydraulic erosion that specify the length, thickness, and location on the bank face of eroded blocks. An empirical discriminant function defines the critical geometry of overhang failures, and the volumes removed by overhang failures are computed using another regression equation. All the regression equations are significant, but have low correlation coefficients, suggesting that cohesive bank erosion has a strong stochastic component. Individual events typically remove small masses of soil (average volume 0·084 m³/m) a few centimeters thick (median = 0·057 m) and a few decimeters in length (median = 0·50 m) from the lower third of the bank. Hydraulic erosion is responsible for 87% of all erosion. When applied to three survey sites not used in its development, the profile model predicts the total volume of erosion with errors of 23%, 5% and 1%. Twenty‐four percent of computed erosion volumes for single events are within 50% of observed volumes at these three sites. Extending the approach to decadal timescales and to entire bends will require three‐dimensional observations of bank failure, and spatially and temporally explicit methods to account for the influence of individual large trees on bank failures and near‐bank hydraulic processes. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

The effects of interdune vegetation changes on eolian dune field evolution: a numerical‐modeling case study at Jockey's Ridge,North Carolina,USA     

Jon D. Pelletier  Helena Mitasova  Russell S. Harmon  Margery Overton 《地球表面变化过程与地形》2009,34(9):1245-1254

Changes in vegetation cover within dune fields can play a major role in how dune fields evolve. To better understand the linkage between dune field evolution and interdune vegetation changes, we modified Werner's (Geology, 23, 1995: 1107–1110) dune field evolution model to account for the stabilizing effects of vegetation. Model results indicate that changes in the density of interdune vegetation strongly influence subsequent trends in the height and area of eolian dunes. We applied the model to interpreting the recent evolution of Jockey's Ridge, North Carolina, where repeat LiDAR surveys and historical aerial photographs and maps provide an unusually detailed record of recent dune field evolution. In the absence of interdune vegetation, the model predicts that dunes at Jockey's Ridge evolve towards taller, more closely‐spaced, barchanoid dunes, with smaller dunes generally migrating faster than larger dunes. Conversely, the establishment of interdune vegetation causes dunes to evolve towards shorter, more widely‐spaced, parabolic forms. These results provide a basis for understanding the increase in dune height at Jockey's Ridge during the early part of the twentieth century, when interdune vegetation was sparse, followed by the decrease in dune height and establishment of parabolic forms from 1953‐present when interdune vegetation density increased. These results provide a conceptual model that may be applicable at other sites with increasing interdune vegetation cover, and they illustrate the power of using numerical modeling to model decadal variations in eolian dune field evolution. We also describe model results designed to test the relative efficacy of alternative strategies for mitigating dune migration and deflation. Installing sand‐trapping fences and/or promoting vegetation growth on the stoss sides of dunes are found to be the most effective strategies for limiting dune advance, but these strategies must be weighed against the desire of many park visitors to maintain the natural state of the dunes. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献