Modeling decadal timescale interactions between surface water and ground water in the central Everglades, Florida, USA

Surface-water and ground-water flow are coupled in the central Everglades, although the remoteness of this system has hindered many previous attempts to quantify interactions between surface water and ground water. We modeled flow through a 43,000 ha basin in the central Everglades called Water Conservation Area 2A. The purpose of the model was to quantify recharge and discharge in the basin's vast interior areas. The presence and distribution of tritium in ground water was the principal constraint on the modeling, based on measurements in 25 research wells ranging in depth from 2 to 37 m. In addition to average characteristics of surface-water flow, the model parameters included depth of the layer of ‘interactive’ ground water that is actively exchanged with surface water, average residence time of interactive ground water, and the associated recharge and discharge fluxes across the wetland ground surface. Results indicated that only a relatively thin (8 m) layer of the 60 m deep surfical aquifer actively exchanges surface water and ground water on a decadal timescale. The calculated storage depth of interactive ground water was 3.1 m after adjustment for the porosity of peat and sandy limestone. Modeling of the tritium data yielded an average residence time of 90 years in interactive ground water, with associated recharge and discharge fluxes equal to 0.01 cm d⁻¹. ³H/³He isotopic ratio measurements (which correct for effects of vertical mixing in the aquifer with deeper, tritium-dead water) were available from several wells, and these indicated an average residence time of 25 years, suggesting that residence time was overestimated using tritium measurements alone. Indeed, both residence time and storage depth would be expected to be overestimated due to vertical mixing. The estimate of recharge and discharge (0.01 cm d⁻¹) that resulted from tritium modeling therefore is still considered reliable, because the ratio of residence time and storage depth (used to calculated recharge and discharge) is much less sensitive to vertical mixing compared with residence time alone. We conclude that a small but potentially significant component of flow through the Everglades is recharged to the aquifer and stored there for years to decades before discharged back to surface water. Long-term storage of water and solutes in the ground-water system beneath the wetlands has implications for restoration of Everglades water quality.     

盾构掘进引起地表沉降的多因素敏感性分析

为了研究各因素在盾构法施工中对地表沉降的影响程度,基于敏感性分析原理,针对一地铁盾构实例,选取土体弹性模量、土仓压力、地下水等3个影响地表沉降的因素,通过变化某一基准参数,让其余影响因素固定,分析研究了盾构施工引起地表沉降对各因素的敏感性。结果如下:弹性模量提高10%时,地表累积最大沉降量可减小15%～20%;在地下水存在的情况下,地表沉降显著增大;而对于砂性土而言,土仓压力越高地表沉降值略有增加。研究结果表明:地表沉降对穿越地层的弹性模量和地下水比较敏感,而对土仓压力敏感性较小。     

Collapse hazard assessment in evaporitic materials from ground penetrating radar: a case study

Evaporitic materials have been studied by means of ground penetrating radar (GPR) in order to evaluate the collapse hazard. The obtained 200 MHz GPR profiles show a low signal-noise ratio over the first 3 m depth, where well-defined and continuous reflectors can be observed. Between 3 and 4.5 m depth, the signal to noise ratio decreases due to attenuation of the electromagnetic (EM) waves. As a result, reflectors located deeper than 3 m become more discontinuous and poorly defined. GPR profiles show trails of continuous and subhorizontal reflectors, with a slightly undulated and irregular geometry. Although some of these reflectors laterally vanish or seem to disappear, sudden interruptions or hyperbolic reflections that could be originated by the occurrence of cavities have not been detected. These reflectors have been interpreted as corresponding to several evaporitic layers (gypsum) that constitute the main lithology in the area. Clear interruptions of reflectors have only been observed in some GPR profiles, and they could be attributed to small (1–2 m long) subvertical faults, with only a few centimetres offset. These faults may be generated by the accommodation of the evaporitic layers to local collapses affecting deeper materials.     

Efficiency of trenches along railways for trains moving at sub- or supersonic speeds

A full 3D analytical approach is adopted to account for trenches on one or both sides close to a railroad. Low-frequency ground vibrations are investigated due to the passing of trains, and open trenches are used as wave barriers. The modelling technique is based on Fourier transforms and Fourier series. The ground is modelled as a layered semi-infinite domain and the embankment with finite layers. The trenches are obtained by simulating the upper surface layer with two or three finite rectangular regions with appropriate widths. A particular boundary condition is adopted at the vertical sides of all finite regions to enable the solution procedure. Rails and sleepers are accounted for with Euler–Bernoulli beams and an anisotropic Kirchhoff plate with transversal isotropy. The wheel loads from the boogie wheel pairs of the train are simulated as moving forces. Hence, no irregularities in rails or wheels are accounted for.     

中国分区地震动衰减关系的确定

本文利用我国丰富地地震工等震线资料,研究了我国烈度衰减关系分区,并建立了分区地震烈度衰减关系。选择既有丰富的强震记录又有烈度衰减关系的美国西部地区作为参考区,并利用本文确定的分区地震烈度衰减关系轩换得到相应的地震动衰减关系式。     

Seismic demands and analysis of site effects in the Marmara region during the 1999 Kocaeli earthquake

The characteristics of the strong ground motion accelerograms from the 1999 Kocaeli earthquake are investigated in detail in this study. The emphasis is on the comparison of the response spectra for the fault normal (FN) and fault parallel (FP) components of the ground motions. The results show that the near-fault records with directivity effects characterize themselves with increased base shear demands rather than increased displacement demands for both the FN and FP components and a narrower velocity sensitive region for the FN component. This study also shows that the effectiveness of base isolation may vary from site to site and for a given site, from component to component. The site effects in the Marmara region during the 1999 Kocaeli earthquake are examined. Site amplifications are predicted by the classical spectral ratio (CSR) and the receiver function (RF) methods. The CSR method gives higher estimates for the site amplifications compared to the RF method and is in better conformity with the observed damage during the Kocaeli earthquake. The districts of Istanbul that are especially susceptible to site amplification hazard are determined. It is apparent from the results that the site amplification hazard risk is the highest for Avcilar and Bakirkoy districts. This study also shows that for sites which have the risk of soil amplification for long-period structures, liquefaction may not be beneficial as a natural base isolator, and may result in shifting the eigenperiod of the low- and mid-rise structures to the critical periods with high site amplifications. This may be especially the case for Avcilar and Bakirkoy districts. In Fatih, Bakirkoy, and Cekmece districts, the predominant period of the ground motion is calculated to be very close to the eigenperiods of the typical residential buildings. Therefore, these three districts are expected to experience heavier damages in future earthquakes due to resonance effects.     

基于遥感技术的开滦煤矿地面塌陷积水动态监测

利用MSS、TM/ETM及CBERS-2数据，对开滦煤矿地面塌陷积水进行了动态监测。通过对4个时相遥感信息的提取，得到了28 a 来开滦煤矿地面塌陷积水的动态信息。结果表明，遥感技术是对矿区地面塌陷积水进行监测的一种很好的方法，在矿区积水信息的 提取中采用CBERS-2数据，可以取得较好的效果。     

The application of the Intermittent SBAS (ISBAS) InSAR method to the South Wales Coalfield,UK

Satellite radar interferometry is a well-documented technique for the characterisation of ground motions over large spatial areas. However, the measurement density is often constrained by the land use, with best results obtained over urban and semi urban areas. We use an implementation of the Small Baseline Subset (SBAS) methodology, whereby areas exhibiting intermittent coherence are considered alongside those displaying full coherence, in the final result, to characterise the ground motion over the South Wales Coalfield, United Kingdom. 55 ERS-1/2 Synthetic Aperture Radar (SAR) C-band images for the period between 1992 and 1999 are processed using the ISBAS (Intermittent Small BAseline Subset) technique, which provides 3.4 times more targets, with associated measurements than a standard SBAS implementation. The dominant feature of the observed motions is a relatively large spatial area of uplift. Uplift rates are as much as 1 cm/yr. and are centred on the part of the coalfield which was most recently exploited. Geological interpretation reveals that this uplift is most likely a result of mine water rebound. Collieries in this part of the coalfield required a ground water to be pumped to enable safe coal extraction; following their closure pumping activity ceased allowing the water levels to return to equilibrium. The ISBAS technique offers significant improvements in measurement density ensuring an increase in detection of surface motions and enabling easier interpretation.     

利用探地雷达(GPR)观测加拿大北极群岛和陆架区海冰厚度空间分布特征

Ground Penetrating Radar(GPR) measurements of sea ice thickness including undeformed ice and ridged ice were carried out in the central north Canadian Archipelago in spring 2010. Results have shown a significant spatial heterogeneity of sea ice thickness across the shelf. The undeformed multi-year fast ice of(2.05±0.09) m thick was investigated southern inshore zone of Borden island located at middle of the observational section,which was the observed maximum thickness in the field work. The less thick sea ice was sampled across a flaw lead with the thicknesses of(1.05±0.11) m for the pack ice and(1.24±0.13) m for the fast ice. At the northernmost spot of the section, the undeformed multi-year pack ice was(1.54±0.22) m thick with a ridged ice of 2.5 to 3 m,comparing to the multi-year fast ice with the thickness of(1.67±0.16) m at the southernmost station in the Prince Gustaf Adolf Sea.     

震源机制对近场地震动反应谱的影响

将欧洲及其毗邻地区以及美国的部分近场强震记录按照震源机制进行分组,详细的分析了震源机制对水平和竖向分量地震动加速度反应谱放大系数以及竖向与水平向反应谱比值的影响.结果表明震源机制对震级不同的地震动以及地震动不同分量反应谱的影响程度不同;震源机制不仅影响反应谱峰值大小以及峰值位置,还在一定程度上影响反应谱的形状.