Digital modeling studies for evaluation of hydrogeological characteristics in Shadnagar granite basin,Andhra Pradesh,India

The use of digital models has increased significantly in recent years with the accessibility of fast computing machines. A variable dimensioned digital model was constructed for the Shadnagar granite basin using SPECTRUM-7 micro computer to integrate various hydrogeological characteristics and for their quantitative evaluation. The basin has an areal extent of 437 sq km and is demarcated with clear water divides in all directions. Transmissivity, recharge and discharge at each cell of the basin area were estimated by trial and error simulation of the hydrogeological phenomenon under steady state condition. Dynamic simulation at representative nodes facilitated the estimation of storage coefficient. The capability of the constructed model was established by the conformance of the simulated hydrographs with the actual behaviour of the ground water system. The entire studies ammended the earlier arrived estimates of various input/output hydrogeological parameters and evolved a methodology for efficient processing of aquifer simulation data     

Low frequency waves in plasmas with spatially varying electron temperature

Low frequency electrostatic waves are studied in magnetized plasmas with an electron temperature which varies with position in a direction perpendicular to the magnetic field. For wave frequencies below the ion cyclotron frequency, the waves need not follow any definite dispersion relation. Instead a band of phase velocities is allowed, with a range of variation depending on the maximum and minimum values of the electron temperature. Simple model equations are obtained for the general case which can be solved to give the spatial variation of a harmonically time varying potential. A simple analytical model for the phenomenon is presented and the results are supported by numerical simulations carried out in a 2.5-dimensional particle-in-cell numerical simulation. We find that when the electron temperature is striated along B₀ and low frequency waves (_ci) are excited in this environment, then the intensity of these low frequency waves will be striated in a manner following the electron temperature striations. High frequency ion acoustic waves (_ci) will on the other hand have a spatially more uniform intensity distribution.     

Chironomids as indicators of climate change: a 100‐lake training set from a subarctic region of northern Sweden (Lapland)

Multivariate numerical analyses (DCA, CCA) were used to study the distribution of chironomids from surface sediments of 100 lakes spanning broad ecoclimatic conditions in northern Swedish Lapland. The study sites range from boreal forest to alpine tundra and are located in a region of relatively low human impact. Of the 19 environmental variables measured, ordination by CCA identified mean July air temperature as one of the most significant variables explaining the distribution and the abundance of chironomids. Lossonignition (LOI), maximum lake depth and mean January air temperature also accounted for significant variation in chironomid assemblages. A quantitative transfer function was created to estimate mean July air temperature from sedimentary chironomid assemblages using weightedaveraging partial least squares regression (WAPLS). The coefficient of determination was relatively high (r² = 0.65) with root mean squared error of prediction (RMSEP, based on jack-knifing) of 1.13 °C and maximum bias of 2.1 °C, indicating that chironomids can provide useful quantitative estimates of past changes in mean July air temperature. The paper focuses mainly on the relationship between chironomid composition and July air temperature, but the relationship to LOI and depth are also discussed.     

The Relative Impact of Regional Scale Land Cover Change and Increasing CO2 over China

A series of 17-yr equilibrium simulations using the NCAR CCM3 (T42 resolution) were performed to investigate the regional scale impacts of land cover change and increasing CO2 over China. Simulations with natural and current land cover at CO2 levels of 280,355, 430, and 505 ppmv were conducted. Results show statistically significant changes in major climate fields (e.g. temperature and surface wind speed) on a 15-yr average following land cover change. We also found increases in the maximum temperature and in the diurnal temperature range due to land cover change. Increases in CO2 affect both the maximum and minimum temperature so that changes in the diurnal range are small. Both land cover change and CO2 change also impact the frequency distribution of precipitation with increasing CO2 tending to lead to more intense precipitation and land cover change leading to less intense precipitation-indeed, the impact of land cover change typically had the opposite effect versus the impacts of CO2. Our results provide support for the inclusion of future land cover change scenarios in long-term transitory climate inodelling experiments of the 21st Century. Our results also support the inclusion of land surface models that can represent future land cover changes resulting from an ecological response to natural climate variability or increasing CO2. Overall, we show that land cover change can have a significant impact on the regional scale climate of China, and that regionally, this impact is of a similar magnitude to increases in CO2 of up to about 430 ppmv. This means that that the impact of land cover change must be accounted for in detection and attribution studies over China.     

川西地区小震重新定位及其活动构造意义

使用双差地震定位法对川西地区1992～2002年的13367个小震进行重新定位， 初步分析了地震活动性与地表活动构造的关系及其揭示的构造信息. 重新定位后，地震活动沿活动断裂成线（带）状分布现象非常突出，呈现出与地表活动构造的密切关系：结构简单的单一走滑断层具有上宽下陡的花状结构特征，拉分盆地与逆断裂具有线性而发散的分布式结构特征，逆断裂之下还存在缺震层. 此外，沿活动断裂带地震活动还具有空间分段性，揭示出局部地段存在着隐伏活动断裂和可圈定为地震危险区的地震空区. 震源深度分布显示，川西高原在15～20km的深度范围内普遍存在厚度约5km的缺震层，以高温高压实验结果为基础，通过计算川西地区地壳强度表明，大约14～19km的深度范围花岗岩处于塑性流变状态，说明缺震层的出现具有地壳物质塑性变形基础.     

江苏浅层低温位地热资源开发利用前景

江苏能源供应的严峻形势促使了地热资源的勘查和开发力度的加大；地热工作的实践和科学技术的进步，逐步扩大了其工作领域；浅层地温作为江苏地热资源开发利用的新领域被提上日程，依据现有资料，认为其前景广阔。     

Reliability analysis of drilled shaft behavior using finite difference method and <Emphasis Type="Italic">Monte Carlo</Emphasis> simulation

Load displacement analysis of drilled shafts can be accomplished by utilizing the “t-z” method, which models soil resistance along the length and tip of the drilled shaft as a series of springs. For non-linear soil springs, the governing differential equation that describes the soil-structure interaction may be discretized into a set of algebraic equations based upon finite difference methods. This system of algebraic equations may be solved to determine the load–displacement behavior of the drilled shaft when subjected to compression or pullout. By combining the finite difference method with Monte Carlo simulation techniques, a probabilistic load–displacement analysis can be conducted. The probabilistic analysis is advantageous compared to standard factor of safety design because uncertainties with the shaft–soil interface and tip properties can be independently quantified. This paper presents a reliability analysis of drilled shaft behavior by combining the finite difference technique for analyzing non-linear load–displacement behavior with Monte Carlo simulation method. As a result we develop probabilistic relationships for drilled shaft design for both total stress (undrained) and effective stress (drained) parameters. The results are presented in the form of factor of safety or resistance factors suitable for serviceability design of drilled shafts.     

Link between convection and meridional gradient of sea surface temperature in the Bay of Bengal

We use daily satellite estimates of sea surface temperature (SST) and rainfall during 1998–2005 to show that onset of convection over the central Bay of Bengal (88–92°E, 14–18°N) during the core summer monsoon (mid-May to September) is linked to the meridional gradient of SST in the bay. The SST gradient was computed between two boxes in the northern (88–92°E, 18–22°N) and southern (82–88°E, 4–8°N) bay; the latter is the area of the cold tongue in the bay linked to the Summer Monsoon Current. Convection over central bay followed the SST difference between the northern and southern bay (ΔT) exceeding 0.75°C in 28 cases. There was no instance of ΔT exceeding this threshold without a burst in convection. There were, however, five instances of convection occurring without this SST gradient. Long rainfall events (events lasting more than a week) were associated with an SST event (ΔT ≥ 0.75°C); rainfall events tended to be short when not associated with an SST event. The SST gradient was important for the onset of convection, but not for its persistence: convection often persisted for several days even after the SST gradient weakened. The lag between ΔT exceeding 0.75°C and the onset of convection was 0–18 days, but the lag histogram peaked at one week. In 75% of the 28 cases, convection occurred within a week of ΔT exceeding the threshold of 0.75°C. The northern bay SST, T _N , contributed more to ΔT, but it was a weaker criterion for convection than the SST gradient. A sensitivity analysis showed that the corresponding threshold for T _N was 29°C. We hypothesise that the excess heating (∼1°C above the threshold for deep convection) required in the northern bay to trigger convection is because this excess in SST is what is required to establish the critical SST gradient.     

2-D Crustal thermal structure along Thuadara-Sindad DSS profile across Narmada-Son lineament,central India

Central India is traversed by a WSW-ENE trending Narmada-Son lineament (NSL) which is characterized by the presence of numerous hot springs, feeder dykes for Deccan Traps and seismicity all along its length. It is divided in two parts by the Barwani-Sukta Fault (BSF). To the west of this fault a graben exists, whereas to the east the basement is uplifted between Narmada North Fault (NNF) and Narmada South Fault (NSF). The present work deals with the 2-D thermal modeling to delineate the crustal thermal structure of the western part of NSL region along the Thuadara-Sindad Deep Seismic Sounding (DSS) profile which runs almost in the N-S direction across the NSL. Numerical results of the model reveal that the conductive surface heat flow value in the region under consideration varies between 45 and 47mW/m². Out of which 23mW/m² is the contribution from the mantle heat flow and the remaining from within the crust. The Curie depth is found to vary between 46 and 47 km and is in close agreement with the earlier reported Curie depth estimated from the analysis of MAGSAT data. The Moho temperature varies between 470 and 500°C. This study suggests that this western part of central Indian region is characterized by low mantle heat flow which in turn makes the lower crust brittle and amenable to the occurrence of deep focused earthquakes such as Satpura (1938) earthquake.     

坝基集中渗漏通道的温度场反分析与试验研究

渗漏是严重影响堤坝安全的主要形式,确定渗漏通道的位置是进行堤坝渗漏整治的前提和基础。温度场探测堤坝渗漏的研究是其中一种较便捷的方法,但是在理论上还需要进一步完善。在库水和地下水存在着温度差异的基础上,考虑堤坝发生集中渗漏后,渗漏通道中的地下水与周围土体进行热量交换,造成渗流通道附近地层温度发生改变,建立起温度场对渗漏通道的反演模型。在前人研究的基础上,考虑地温梯度的影响,可以建立有集中渗漏通道影响下的二维热传导方程,进而以现场测井的温度数据作为边界条件,对泛定方程进行求解,最终得到渗漏通道的位置。计算结果和实测结果的对比表明,通过温度场反推渗漏通道参数的方法是可行的。