Elastic properties of granulite facies rocks of Mahabalipuram, Tamil Nadu, India

Compressional and shear wave velocities and attenuation measurements have been carried out in some of the borehole samples of acidic, basic and intermediate granulites of Mahabalipuram, Tamil Nadu, India. The results have been obtained at ambient conditions using ‘time-of-flight’ pulse transmission technique at 1.0 MHz frequency. The results show linear relationships between velocity and density, and velocity and attenuation properties of the rocks. The acidic granulites show lower velocities and higher attenuation than the intermediate and basic granulites. The average values of the Poisson’s ratio of acidic, intermediate and basic granulites have been found to be 0.210, 0.241 and 0.279 respectively. The variations in velocities and attenuation in these low porosity crystalline rocks are found to be strongly influenced by their mineral composition. The laboratory velocity data (extrapolated to high pressure) of the present study and the published field velocity data from deep seismic sounding studies indicate that these granulite facies rocks may belong to mid-crustal depths only.     

Control of dust emissions by geomorphic conditions, wind environments and land use in northern China: An examination based on dust storm frequency from 1960 to 2003

The degree to which dust emissions are controlled by geomorphic conditions, wind environments and land use was investigated using the dust storm frequency (DSF) and data from more than 300 meteorological stations throughout northern China. Our analysis showed that most dust emissions originated in gobi deserts that developed in piedmont alluvial fans of the Kunlun, Qilian and Helan mountains. Dust emissions are low from other gobi desert regions, such as the northern Gurbantunggut and eastern Taklimakan, where high vegetation coverage restrained dust emissions or where dust-size particles are not abundant after a long period of strong wind erosion. Sandy deserts with relatively high vegetation coverage or an extensive cover by mobile sands are not a major dust source. Although the highest dust emissions did not appear in regions with the highest wind energy, DSF trends in each region from 1960 to 2003 were closely related to local wind activity. DSF was low in regions with high levels of human activity, where the mean DSF from 1960 to 2003 did not exceed 4 days/year; even from the 1960s to the early 1970s, the period with the greatest DSF, frequency did not exceed 8 days/year, which indicates that extensive land use did not contribute to DSF. The low DSF in these areas might result from the fact that although land use could produce abundant fine soil fractions, vegetation coverage and soil moisture remained higher than in the gobi deserts of arid China, thereby decreasing dust-storm occurrence.     

Flood seasonality and generating conditions in the Tay catchment, Scotland from 1200 to present

The new maximum recorded river flows in Scotland since 1988 have triggered widespread interest in whether floods are becoming more frequent and in the conditions that generate floods of different magnitudes and frequencies. There are questions about the longer-term variability in flood-generating characteristics, and whether there are past analogues for present hydroclimatic variability. The present paper builds on previous work reconstructing a detailed historic flood chronology for the Tay, the largest catchment in Scotland, and its tributaries over the past 800 years, extending the gauged discharge record (1952 onwards). It categorizes flood-generating factors in the Tay catchment and analyses the hydro-meteorological conditions that have generated extreme and moderate floods over a historical period. This work is placed in a broader literature context of historical 'climaxes of storminess', periods of higher storm frequency, flood patterns observed in Scotland and Europe during the Little Ice Age and longer-term rainfall and temperature patterns. The paper concludes that the variability in flood-generating characteristics is highly dependent on the timescale of observation. Inevitably the relative dominance of winter and early spring flooding can vary from year to year and within specific time-periods, but so can the level of augmentation of the flood series with summer and autumn floods to produce notable 'flood years' and flood clusters. The Tay provides a good 'all-Scotland surrogate' for historical flood patterns, reflecting its gathering areas in eastern and western Scotland. The value of a historical approach to the assessment of flood seasonality and generating characteristics is clearly demonstrated.     

大湾铀矿田铀-镭平衡系数及迁移富集特征研究

从分析大湾铀矿田各矿床(点)的铀镭平衡系数变化特征出发,结合放射性同位素比值特征分析铀镭迁移富集行为,指出了各矿床(点)氧化带的深度,以了解各铀矿床(点)潜在的工业价值.     

库车坳陷侏罗系煤成气动力学模拟研究

应用黄金管—高压釜封闭体系热模拟实验与GC、GC-IRMS分析技术,结合KINETICS专用软件,对库车坳陷侏罗系煤成气进行了动力学模拟研究。库车坳陷侏罗系煤具有高的产气性,在高演化阶段主要产甲烷气;侏罗系煤热解气甲烷碳同位素为-36‰～-25‰,乙烷碳同位素为-28‰～-16‰;甲烷、C2-C5气态烃的生成活化能分别为(47～64k)calm/ol、(55～72k)calm/ol,频率因子各为5.265×1013s-1、5.388×1018s-1。在此基础上,进一步探讨了克拉2气田天然气的成因。研究认为,克拉2气田天然气属阶段捕获的煤成气,主要聚集了5～1Ma时期的天然气,其成熟度Ro分布范围为1.3%～2.5%。     

VSP资料约束地层反滤波研究

浅地表的低速带和地层滤波作用导致地震信号的能量衰减,地震子波的高频快速衰减,速度频散的子波变形,对地震底层分析带来了严重的影响。地层反滤波算法就是为了消除地层对子波的影响,利用VSP中的直达下行波推算出每个地层滤波算子,计算出各个地层滤波算子的反算子,然后利用这些反算子恢复出地表记录中损失掉的高频成分,减弱地层滤波对波形的影响,增加地表记录的频率成分和波形的准确度。分析实际地震资料表明,经过地层反滤波处理后的记录频率成分明显提升,地质构造更加准确、清晰。     

深层地震勘探激发井深探讨

深层地震勘探野外资料采集的关键是在保证原始资料一定信噪比的基础上,同时兼顾分辨率,激发井深是决定资料品质的重要因素之一。通过对虚反射滤波作用分析,提出了充分利用虚反射能量设计最佳激发井深,增强下传地震波能量的采集方法。理论分析和试验资料表明,在高速层下4～7m的最佳激发岩性深度是深层勘探的理想井深。     

生物去除地下水中硫酸盐的实验研究

使用平皿夹层厌氧法分离得到纯化的硫酸盐还原菌,通过对比封口、敞口两种情况下细菌培养过程中产生的现象和细菌的生长曲线,表明SRB并非严格的厌氧菌,能耐受一定浓度的环境溶解氧.将该菌用于去除溶液中的SO42-,发现SRB在还原SO42-的过程中,随着SO42-去除率的增加,溶液的pH值会减小,而当SO42-去除率降低时,溶液的pH有增加的趋势;COD/SO42-比值对SO42-的去除率有很重要的影响,在封口情况下,COD/SO42-=0.75时SO42-的最大去除率约为48.60%,COD/SO42比值增加至2.5时,SO42-最大去除率可以达到89.72%,要达到SO42-高去除率,必须增加COD/SO42-比值.     

直升机载频率域电磁系统在我国环境和工程勘查中的应用前景

本文根据国际上采用直升机载频率域电磁系统进行环境和工程勘查的应用效果,结合我国引进的航空电磁系统的性能和特点,探讨了采用直升机载频率域电磁系统在我国进行环境和工程勘查的应用前景。     

低频泥石流特征及防治 --以四川汶川县茶园沟为例

低频泥石流指30a以上发生1次的泥石流。尽管发生频率很低，但由于自身的特征及人们认识上的原因，其造l戒的人员伤亡和财产损失却居各类泥石流之首。对低频泥石流的研究在预防和减轻泥石流灾害方面有着重要意义。文章以2003年8月9日发生在四川汶川县茶园沟的泥石流为蒯，采用形态调查法和称重法等方法确定了流量、流速及重度。分析了其物质来源及形成的自然和人为原因，探讨了低频泥石流的特征。针对低频泥石流的低频性、破坏性和隐蔽性特点，同时考虑到低频泥石流沟的防治受保护对象的重要程度及资金投入等因素的限制，提出了进行泥石流危险性分区、搞好小流域水土深持、普及泥石流防灾减灾知识及加强监测和预警预报等措施，这对减轻低频泥石流区的灾害有一定的借鉴意义。