Timescales of seawater intrusion and retreat

Quantifying the timescales associated with moving freshwater–seawater interfaces is critical for effective management of coastal groundwater resources. In this study, timescales of interface movement in response to both inland and coastal water level variations are investigated. We first assume that seawater intrusion (SWI) and retreat (SWR) are driven by an instantaneous freshwater-level variation at the inland boundary. Numerical modelling results reveal that logarithmic timescales of SWI (lnT_i) and SWR (lnT_r) can be described respectively by various simple linear equations. For example, SWI timescales are described by lnT_i = a + blnh′_f–s, where a and b are linear regression coefficients and h′_f–s is the boundary head difference after an instantaneous drop of inland freshwater head. For SWR cases with the same initial conditions, but with different increases in freshwater head, lnT_r = c + dΔX_T, where c and d are regression coefficients and ΔX_T is the distance of toe response that can be estimated by a steady-state, sharp-interface analytical solution. For SWR cases with the same freshwater head increase, but with different initial conditions, in contrast, lnT_r = e + flnΔX_T, where e and f are regression coefficients. The timescale of toe response caused by an instantaneous variation of sea level is almost equivalent to that induced by an instantaneous inland head variation with the same magnitude of water level change, but opposite in direction. Accordingly, the empirical equations of this study are also applicable for sea-level variations in head-controlled systems or for simultaneous variations of both inland and coastal water levels. Despite the idealised conceptual models adopted in this study, the results imply that for a particular coastal aquifer, SWI timescales are controlled by the boundary water levels after variations, whereas SWR timescales are dominated by the distance of toe response.     

Wood biomass functions for Acacia abyssinica trees and shrubs and implications for provision of ecosystem services in a community managed exclosure in Tigray,Ethiopia

In the Ethiopian highlands, remarkable recovery of vegetation has been achieved using exclosures, protecting vegetation against livestock browsing and firewood harvesting. But these emerging forest resources require tools for sustainable use, implying knowledge on biomass stocks and growth. In this study we developed biomass functions estimating total, stem and branch biomass from diameter at stump height (DSH) and tree height (H) for an 11-year old exclosure in Tigray, Ethiopia. In a systematic grid of 55 plots, DSH and H of all trees and shrubs were recorded. 40 Acacia abyssinica trees were selected for destructive sampling. Allometric relationships using a natural log–log model were established between aboveground biomass, DSH and H. Models with only DSH were found best with R² between 0.95 and 0.98. The functions were 10 fold cross-validated and R²_{_}cv ranged from 0.94 to 0.97, indicating good model performance. The models were found well in range with those of other seasonal forests in East Africa. Total aboveground biomass was estimated 25.4 ton ha⁻¹ with an annual production of 2.3 ton ha⁻¹, allowing sustainable wood fuel use for 4 persons ha⁻¹. The presented predictive functions help to harmonize between ecological and societal objectives and are as such a first step towards an integrated planning tool for exclosures.     

希尔伯特-黄变换在地震资料处理中的应用

希尔伯特-黄变换是最新发展起来的处理非线性非平稳信号的时频分析方法.本文介绍了该方法的基本原理和几个关键技术,以及其优势所在,并将它应用于含随机噪音的地震信号和实际地震资料的分解.分解后的信号能够重构原始信号,重构后在信噪比和分辨率方面有了一定的提高,对地震资料的去噪有重要意义.     

芦山7级地震的同震位移估计和震源滑动模型反演尝试

利用自动经验基线校正方法,分析2013年4月20日芦山M_S7.0级地震13个近场强震动台的观测资料,以估算同震位移场分布,并据此反演了震源滑动模型.经与GPS结果比较,两种不同方法给出的芦山7级地震的水平近场同震位移场幅度都不超过cm级,均显示为典型的逆冲型地震（兼有少量左旋走滑错动）.强震最大水平和垂直永久位移分别为4.9 cm和4.4 cm,分别出现在51YAM台和51QLY 台.两种资料反演的震源滑动模型虽显示多事件特征,但主要滑动均集中在第一次事件,即初始滑动点两侧的走向长约30 km、倾向长约25 km的相对集中的较小范围内,强震和GPS模型的最大滑动量分别为1.14 m和1.09 m,较为一致.其余子事件滑动量小且分布零散,不能排除其数值效应的因素.反演矩震级均在M_w6.7左右,地表破裂应该不明显.文章还讨论了目前在我国利用近场强震动记录估计M_w6~7级地震同震位移场存在的困难和问题,为今后类似工作提供参考.     

经验模态分解法在安徽省南部地下流体分析中的应用

首次引进经验模态分解法（EMD）对安徽省南部地下流体进行分析。通过对地下流体数据的分解与重构,发现该方法能提取不同尺度的水位动态,效果较好。通过对震例的总结发现：显著地震前、后安徽省南部地下流体EMD重构结果均出现异常,且存在某些地震前兆敏感点。同时,还对地震前地下流体的变化原因进行了初步分析。     

Engineering geological studies of the diversion tunnel, focusing on stabilization analysis and support design, Iran

In this paper a detailed engineering geological assessment of rock masses and support design studies at Garmi Chay dam site, has been carried out. This project is located in the northwest of Iran and will be used for flow control and water storage. The diversion tunnel of the dam has a diameter of 5.5 m and a length of 420 m and will be driven in slightly to highly weathered micaschist and trachy andesite rock units. The geological studies include field and laboratory investigations that based on the results; for more exact investigation, tunnel alignment was divided into three geotechnical zones. These zones consist mainly of highly weathered gray micaschists, dark red trachy andesites and slightly weathered gray micaschists, respectively. Then, for every zone, support capacity of rock masses was evaluated by means of empirical and numerical methods. The rock mass classification systems (RMR, Q, GSI, RSR, SRC and RMi), the convergence–confinement method and a 2D finite element computer software, Phase² were used for empirical and numerical method, respectively. According to the results acquired from these methods some stability problems were expected in the tunnel especially in highly weathered micaschist zone, so that in practice two big collapses occurred. Because of high weathering, low constants of rock masses and their soil-like behavior, the stability analysis by analytical method does not give illogical results in lightly weathered micaschist zone. The support system, suggested by empirical method, was applied and its performance was evaluated by means of numerical modeling. After installation the support suggested by Phase² program, the thickness of plastic zone and deformations around the tunnel decreased significantly. Consequently the agreement of these methods with each other was resulted and using combination of them was recommended for more reliable support design.     

EFFECT OF DIGITAL ELEVATION MODEL RESOLUTION ON EMPIRICAL ESTIMATION OF SOIL LOSS AND SEDIMENT TRANSPORT WITH GIS

The horizontal accuracy of topographic data represented by digital elevation model (DEM) resolution brings about uncertainties in landscape process modeling with raster GIS. This paper presents a study on the effect of topographic variability on cell-based empirical estimation of soil loss and sediment transport. An original DEM of 10m resolution for a case watershed was re-sampled to three realizations of higher grid sizes for a comparative examination. Equations based on the USLE are applied to the watershed to calculate soil loss from each cell and total sediment transport to streams. The study found that the calculated total soil loss from the watershed decreases with the increasing DEM resolution with a linear correlation as spatial variability is reduced by cell aggregation. The USLE topographic factors (LS) extracted from applied DEMs represent spatial variability, and determine the estimations as shown in the modeling results. The commonly used USGS 30m DEM appears to be able to reflect essential spatial variability and suitable for the empirical estimation. The appropriateness of a DEM resolution is dependent upon specific landscape characteristics, applied model and its parameterization. This work attempts to provide a general framework for the research in the DEM-based empirical modeling.     

一种去除地震背景噪音的新方法

结合希尔伯特-黄变换方法,根据信号背景噪音时间延续性假设,提出了一种自适应地震信号去噪算法。利用该算法实现了台站地震监测信号的去噪分析。分析表明：1）该去噪算法能根据背景信号特性有效去除信号的低频干扰;2）该算法可自适应完成信号分解去噪,计算效率高,无时间分辨率和频率分辨率问题;3）该算法处理高频干扰存在缺陷,有待进一步完善。     

地震海洋学方法在海洋混合参数提取中的研究与应用——以南海内波和地中海涡旋为例

混合是海洋中普遍存在的一种海水运动形式,对多个海洋学分支的研究具有重要的影响.随着物理海洋学的研究重心从大尺度向中小尺度现象过渡,近年来混合问题的研究重心也逐渐转向了中小尺度现象.内波与中尺度涡都是非常重要的中小尺度物理海洋学现象,对海洋能量在不同尺度中的级联发挥着重要的作用.本文基于地震海洋学研究了海洋混合参数的提取方法,并以南海内波和地中海涡旋为例进行了计算和分析.结果显示,南海内波在200~600m深度范围内所引起的混合可达10-2.79 m2·s-1左右,比大洋的统计结果10-5 m2·s-1高出两个数量级以上.而地中海涡旋所引起的湍流混合率可达10-3.44 m2·s-1左右,与大洋统计结果相比高出1.5个数量级左右,并且地中海涡旋下边界的混合要强于上边界,这一特征与前人的研究一致,另外涡旋上边界之上以及侧边界的外侧也具有非常高的混合率.