Application of perfectly matched layers in the transient analysis of dam–reservoir systems

The transient analysis of dam–reservoir systems by employing perfectly matched layers has been investigated. In previous studies, boundary conditions of the PML region in the reservoir have been neglected. In this paper, they are incorporated completely in the formulation. Moreover, a technique is introduced to involve the effect of incident waves caused by vertical ground motions at the reservoir bottom in the analysis. Performing several numerical experiments indicates that applying boundary conditions of the PML domain and utilizing the proposed method for vertical excitation cases reduce the computational cost significantly and make the PML method a very efficient approach for the transient analysis of dam–reservoir systems.     

Sampling efficiency in Monte Carlo based uncertainty propagation strategies: Application in seawater intrusion simulations

The implementation of Monte Carlo simulations (MCSs) for the propagation of uncertainty in real-world seawater intrusion (SWI) numerical models often becomes computationally prohibitive due to the large number of deterministic solves needed to achieve an acceptable level of accuracy. Previous studies have mostly relied on parallelization and grid computing to decrease the computational time of MCSs. However, another approach which has received less attention in the literature is to decrease the number of deterministic simulations by using more efficient sampling strategies. Sampling efficiency is a measure of the optimality of a sampling strategy. A more efficient sampling strategy requires fewer simulations and less computational time to reach a certain level of accuracy. The efficiency of a sampling strategy is highly related to its space-filling characteristics.This paper illustrates that the use of optimized Latin hypercube sampling (OLHS) strategies instead of the widely employed simple random sampling (SRS) and Latin hypercube sampling (LHS) strategies, can significantly improve sampling efficiency and hence decrease the simulation time of MCSs. Nine OLHS strategies are evaluated including: improved Latin hypercube sampling (IHS); optimum Latin hypercube (OLH) sampling; genetic optimum Latin hypercube (GOLH) sampling; three sampling strategies based on the enhanced stochastic evolutionary (ESE) algorithm namely φ_p-ESE which employs the φ_p space-filling criterion, CLD-ESE which utilizes the centered L₂-discrepancy (CLD) space-filling criterion, and SLD-ESE which uses the star L₂-discrepancy (SLD) space-filling criterion; and three sampling strategies based on the simulated annealing (SA) algorithm namely φ_p-SA which employs the φ_p criterion, CLD-SA which uses the CLD criterion, and SLD-SA which utilizes the SLD criterion. The study applies SRS, LHS and the nine OLHS strategies to MCSs of two synthetic test cases of SWI. The two test cases are the Henry problem and a two-dimensional radial representation of SWI in a circular island. The comparison demonstrates that the CLD-ESE strategy is the most efficient among the evaluated strategies. This paper also demonstrates how the space-filling characteristics of different OLHS designs change with variations in the input arguments of their optimization algorithms.     

How can the uncertainty in the natural inflow regime propagate into the assessment of water resource systems?

The Canadian Rocky Mountain headwaters support the water resource systems of the Canadian Prairies. Significant variations in natural headwater contributions have been observed due to warming climate. Projecting future natural headwater flows under climate change effects, however, has large uncertainty. First, there are difficulties in climate modeling and downscaling in alpine regions. Second, streamflow modeling in mountainous areas is extremely challenging. There is therefore a need to understand the effects of uncertainty in the natural inflow regime, and in particular how this translates into uncertainty in representing the state and the outflow of water resource systems. Considering the Oldman River basin in Alberta, Canada, we synthesized different inflow regimes based on site/inter-site properties of the historical inflow regime. The water resources system was then conditioned on the synthesized inflow regimes to identify the mechanisms of error propagation from the headwater streamflows to the water allocations. The results show that the response of the water resource system to the uncertainty in the generated inflow regime depends on the system state, flow condition and the component of interest. Generally, the response of the reservoirs to the uncertainty in the estimated inflow regime is more significant in dry years, in particular during low flow conditions. The response at the system outlet is rather different, as the propagation of the headwater uncertainty is more significant during high flow conditions. Also, similar inflow estimates in terms of error and uncertainty may result in different error and uncertainty estimates in the simulated outflows; therefore, lower bias and uncertainty in estimating the regional inflow regime does not necessarily mean lower bias and uncertainty in simulating the streamflow at the outlet of the system. Our results provide improved understanding of uncertainty propagation through complex water resource systems, but also portray the need for better climate and hydrological modeling in the Rocky Mountains for improved water management in the Canadian Prairies, particularly in the face of uncertain climate futures. This will be crucial if the natural headwater inflows decline and/or the system faces drought conditions.     

芦山M7．0地震余震分布特征

使用双差定位方法,对2013年4月20日08时02分芦山 M 7．0地震后近10天的余震进行重新定位,获得精度较高的重定位结果;在此基础上,对余震空间分布特征进行研究,推测芦山主震的发震断层可能为大川-双石主断裂东侧的一条次级隐伏逆冲断层。     

泉州盆地地震效应特征的一维等效线性和二维非线性分析的比较

采用等效线性动粘弹性模型描述土的动力非线性特性,基于一维等效线性波传法,对泉州盆地地震效应进行了分析;同时,采用修正Martin-Seed-Davidenkov动粘弹塑性模型描述土的动力非线性特性,对泉州盆地非线性地震效应进行了大尺度二维精细化有限元分析,研究了地形地貌和土层横向不均匀性对地震效应的影响。将两种分析结果进行对比,结果表明：①随着基岩输入地震动强度增大,地表峰值加速度PGA放大效应总体呈现减小趋势,中震与小震、大震与小震的地表PGA放大系数之比依次为0.83~0.99、0.72~0.97;②该盆地Ⅲ类场地处,基岩、地表起伏不大,且土层横向分布较均匀,两种方法计算得到的地震效应特征类似;基岩或地表起伏剧烈、土层横向分布明显不均匀的Ⅱ类场地上,二维非线性分析给出的地表PGA放大系数明显大于一维等效线性结果,两种方法得到的地表加速度反应谱及PGA随土层深度的变化特征存在显著差异,二维非线性分析给出的地表加速度反应谱大多呈现双峰甚至多峰现象,且PGA在土层特定深度处存在聚集效应,使PGA随土层深度的变化呈现非单调性。     

Spectral-element simulations of elastic wave propagation in exploration and geotechnical applications

We apply the spectral-element method (SEM), a high-order finite-element method (FEM) to simulate seismic wave propagation in complex media for exploration and geotechnical problems. The SEM accurately treats geometrical complexities through its flexible FEM mesh and accurately interpolates wavefields through high-order Lagrange polynomials. It has been a numerical solver used extensively in earthquake seismology. We demonstrate the applicability of SEM for selected 2D exploration and geotechnical velocity models with an open-source SEM software package SPECFEM2D. The first scenario involves a marine survey for a salt dome with the presence of major internal discontinuities, and the second example simulates seismic wave propagation for an open-pit mine with complex surface topography. Wavefield snapshots, synthetic seismograms, and peak particle velocity maps are presented to illustrate the promising use of SEM for industrial problems.     

四川盆地熊坡背斜构造特征及其成因机制

基于地震剖面解释、数字高程模型、历史地震、测年数据及钻孔等资料,分析了四川盆地熊坡背斜的构造特征、运动学特征及其成因机制。结果显示：(1)熊坡背斜与蒲江-新津断裂空间展布上具有较强的一致性,表现出断层传播褶皱模型,变形显著,缩短量为7.2 km,缩短率约为30％;(2)熊坡背斜隆起于(1.0±0.2) MaB.P.之后,且中更新世早期及晚更新世曾发生过强烈活动,使背斜两侧第四系厚度产生明显差异;(3)蒲江-新津断裂现今地震活动明显且小震频繁,曾有Ms=5.0～5.9的地震历史记录;(4)来自龙门山与扬子克拉通的挤压应力以及断层-滑脱作用是形成熊坡背斜的主要应力机制。熊坡背斜并非均匀应力下连续变形的产物,而是由于断裂活动时发生快速抬升而形成的。     

Three‐dimensional Evolutionary Models of the Qiongxi Structures,Southwestern Sichuan Basin,China: Evidence from Seismic Interpretation and Geomorphology

Fold terminations are key features in the study of compressional fault-related folds. Such terminations could be due to loss of displacement on the thrust fault or/and forming a lateral or oblique ramp. Thus, high-quality seismic data would help unambiguously define which mechanism should be responsible for the termination of a given fault-related fold. The Qiongxi and Qiongxinan structures in the Sichuan Basin, China are examples of natural fault-propagation folds that possess a northern termination and a structural saddle between them. The folds/fault geometry and along-strike displacement variations are constrained by the industry 3-D seismic volume. We interpret that the plunge of the fold near the northern termination and the structural saddle are due to the loss of displacement along strike. The fault geometry associated with the northern termination changes from a flat-ramp at the crest of the Qiongxinan structure, where displacement is the greatest, to simply a ramp near the northern tip of the Qiongxi structure, without forming a lateral or oblique ramp. In this study, we also use the drainage pattern, embryonic structure preserved in the crest of the Qiongxinan structure and the assumption that displacement along a fault is proportional to the duration of thrusting to propose a model for the lateral propagation of the Qiongxinan and Qiongxi structures. Specifically, we suggest that the structure first initiated as an isolated fault ramp within brittle units. With increased shortening, the fault grows to link with lower detachments in weaker shale units to create a hybridized fault-propagation fold. Our model suggests a possible explanation for the lateral propagation history of the Qiongxinan and Qiongxi structures, and also provides an alternative approach to confirming the activity of the previous Pingluoba structure in the southwestern Sichuan Basin in the late Cenozoic.     

2007/2008年冬季平流层环流异常及平流层—对流层耦合特征

利用NCEP/NCAR再分析资料,分析了2007/2008年冬季平流层环流振荡的过程和异常特征,以及平流层—对流层的环流耦合特征。结果发现：2007/2008年冬季平流层极涡持续偏强,且极涡从12月下旬开始向东亚—大西洋地区偏心发展,同时在欧洲—地中海地区减弱向极区收缩,从而在欧亚地区的平流层高层最早形成“一脊一槽”1波型的环流形势;该平流层的环流异常信号逐步向低层传播;从平流层10 hPa向下传播到对流层中、低层需要约15~20天的时间;此时对流层500 hPa上,与平流层向下传播的信号相对应,呈现为高纬度“西高东低”和副热带“东高西低”的环流异常型,即分别对应着乌拉尔山阻塞高压、鄂霍茨克海低槽以及副热带高压异常偏强和副热带欧亚大陆中西部低槽活动频繁。这种环流异常配置即形成了有利于我国南方降雪持续的大尺度背景条件。进一步研究还发现,平流层异常信号存在由热带向极传播的趋势。2008年1月的平流层极涡振荡正异常所对应的环流异常信号可以追溯到2007年秋季10月份最早出现在热带地区的环流异常信号,该异常信号在向极传播过程中同时向东移动,2008年1月传播到极区,对应极涡振荡的正异常。说明前期平流层的异常信号及其演变,对2008年1月的气候异常具有重要指示意义。