直流激电测深二维反演的若干问题研究

目前,激电数据的二维反演主要针对高密度激电数据,而对于常规的激电测深则很少涉及.据此,针对常规激电测深二维反演所涉及到的一些技术难点进行探讨.在正演过程中,根据实测数据实现有限元网格自动剖分,并采用双网格系统,用相邻节点电导率双线性连续进行有限元模拟,并对模拟的误差进行校正.在反演过程中,利用互换原理和Broyden的方法计算偏导数矩阵;采用与奇异值分解算法精度相当的共轭梯度算法求解偏导数矩阵方程.最后通过对模拟数据和实测数据进行反演试算,验证本计算方法是可行的.     

地面-坑道激电测深方法在山东玲珑断裂带深部找矿中的应用

在山东玲珑断裂带深部找矿中,考虑断裂带处在地电干扰和地形变化复杂地段,且深部地质体产状变化较大,仅依据半空间地面物探方法很难摸清地质体的展布形态,盲目布设钻孔会造成找矿成本的提高。为精确反演深部矿体的边界范围、走向及倾向,提高钻孔见矿率,降低找矿成本,在山东玲珑断裂带地面、坑道采用立体物探技术,试验通过布设多条方位不同的地-坑、坑-坑和地-地纵横激电中梯剖面和双向三极测深剖面,进行了二维电法剖面反演。在地面-坑道激电测深方法中,地面-坑道供电,坑道测量探测深度与坑道深度呈正相关,反映了深部巷道底板以下电阻率和极化率的分布状况,可以实现深地探测目的。由于地面-坑道供电,坑道测量装置处在半空间和全空间两个部分,需要采用"镜像法"和地下倾斜偶极源电流场特征对其装置系数k值重新推导,以反映坑道空间岩矿体真实电阻率的变化。坑道中梯剖面异常与单向三极剖面异常、双向三极电测深反演结果对应较好。经钻探验证,矿体分布与物探推断高极化体基本一致,为快速准确布设深部钻孔提供资料。     

佘山重力垂直梯度偏小的原因及其对大地测量的影响

根据推导的公式计算了由山体质量引起的梯度效应,结果与实测值甚为接近。分析了佘山重力垂直梯度偏小的原因,认为这是由于山体质量分布引起的。最后讨论了垂直梯度偏小对重力值的高度归算和大地水准面的影响。     

Longshore variations in nearshore wave processes at magilligan point,northern ireland

Magilligan Point is a recurved cuspate foreland at the mouth of Lough Foyle. Two wave regimes intersect in the estuary mouth and the manner of their interplay controls shoreline changes. Ocean swell waves from the N and NE are refracted around the recurve, losing both height and energy longshore. Width of the surf zone decreases and waves tend to steepen, although both these changes and wave refraction owe something to nearshore geometry. Angle of wave approach becomes more acute and a westerly flowing longshore current moves sand S and SW along the beach. Estuary waves from the S and SW are wind-driven with high-frequencies and steepnesses. They generate a northeasterly current which returns material N, but dies out as the waves become obliterated by nearshore attenuation and breaking of swell. It is possible to identify a time-averaged null-point where shoreline wave power is balanced, although this tends to shift over short periods causing rapid morphological changes. The existence of two independent, but counteractive cells ensures the long-term maintenance of the foreland, without requiring major or continuous supplies of fresh sediment.     

利用不完全Cholesky共轭梯度法求解点源三维地电场

点源三维地电场的求解是一大型数值计算问题．本文用有限差分方法求解,最后形成一个线性方程组Ax＝b,这里A是大型稀疏的带状对称矩阵．解大型稀疏方程组的完全Cholesky分解直接算法,一般要求巨大的机器内存来存储系数矩阵A,而且计算速度极慢．因此引入不完全Cholesky共轭梯度（ICCG）算法及按行索引的稀疏存储模式,充分利用A的稀疏性,使得计算速度大大提高,而内存要求则大大减少,因此ICCG算法是地电三维正演的强有力工具．     

Slope form and basal stream relationships: Some further comments

The nature and strength of the correlation between stream gradient and valley side slope angle are seen to vary according to the order of the stream segment. In addition, it is suggested that the relationship will depend on the efficiency of slope processes, and that this may contribute to tye different from of relationship obtained in different regions.     

Rainfall,runoff and shallow groundwater response in a mixed-use,agro-forested watershed of the northeast,USA

Stream and shallow groundwater responses to rainfall are characterized by high spatial variability, but hydrologic response variability across small, agro-forested sub-catchments remains poorly understood. Conceivably, improved understanding in this regard will result in agricultural practices that more effectively limit nutrient runoff, erosion, and pollutant transport. Terrestrial hydrologic response approaches can provide valuable information on stream-aquifer connectivity in these mixed-use watersheds. A study was implemented, including eight stream and co-located shallow groundwater monitoring sites, in a small sub-catchment of the Chesapeake Bay watershed in the Northeast, USA to advance this ongoing need. During the study period, 100 precipitation-receiving days (i.e., 24-hour periods, midnight to midnight) were observed. On average, the groundwater table responded more to precipitation than stream stage (level change of 0.03 vs. 0.01 m and rainfall-normalized level change estimate of 3.81 vs. 3.37). Median stream stage responses, groundwater table responses, and response ratios were significantly different between sub-catchments (n = 8; p < 0.001). Study area average precipitation thresholds for runoff and shallow groundwater flow were 2.8 and 0.6 cm, respectively. Individual sub-catchment thresholds ranged from 0.5 to 2.8 cm for runoff and 0.2 to 1.3 cm for shallow groundwater flow. Normalized response lag times between the stream and shallow groundwater ranged from −0.50 to 3.90 s·cm⁻¹, indicating that stormflow in one stream section was regulated by groundwater flow during the period of study. The observed differences in hydrologic responses to precipitation advance future modelling efforts by providing examples of how terrestrial groundwater response methods can be used to investigate sub-catchment spatial variability in stream-aquifer gradients with co-located shallow groundwater and stream stage data. Additionally, results demonstrate asynchronous stream and shallow groundwater responses on precipitation-receiving days, which may hold important implications for modelling hydrologic and biogeochemical fate and transport processes in small, agro-forested catchments.     

�������������ݶ����ݵ��ܶȷ����о�

???????????????????????????????????????????????????????????桢????????????????????Tesseroid??????????????ù????????????????(ART)????????????????????????????????????????飬???????????????趨?????б???????     

渭河盆地西安凹陷地热田热储特征及开发方式

热源、热储层(砂体厚度、孔隙度、渗透率)、地温场等是影响地热资源评价的重要因素。本文以渭河盆地西安凹陷-西安市延长石油西化小区为例,在收集前人资料的基础上,应用地层测温、测井、岩芯分析等资料,分析了研究区地温场特征、热储层特征及地热资源量,运用多种参数对热储层有利区进行了综合评定。研究结果表明延长石油西化小区属地热异常区,地温梯度为3.5℃/100 m;研究区张家坡组、蓝田灞河组砂泥岩互层发育,砂厚分布在40～140 m之间,平均孔隙度分布在15.68%～30.3%之间,蓝田灞河组砂层厚度、地层热量、含水量和总热量均高于三门组和张家坡组地层,地热开发条件最好;综合考虑砂体厚度、地层含水量、地温梯度、地温、热储层物性因素,认为西安凹陷延长石油西化小区地热开发应选择蓝田灞河组为主要目的层段,最优的地热开发方式应采用采灌平衡法进行地热开采,综合考虑研究区更宜选择中深层地埋管井下换热方式进行地热资源开发。     

空间特性约束的县域耕地生产效益评价——以紫云苗族布依族自治县为例

本文以紫云苗族布依族自治县为试点,首先利用地理信息空间分析技术,分析评价耕地空间特征、农业物资运输配套设施空间分布、农业灌溉资源空间分布等因子对耕地生产效益的影响。然后从地理国情普查、耕地地球化学质量调查等成果数据中甄选影响因子,构建影响因子样本集,提出梯度距离概念,计算等级耕地经济效益权重,并构建偏最小二乘回归模型,评价各因子对耕地生产效益的影响。最后从地理空间角度提出了提升县域农业生产效益的改良措施。