地磁场水平梯度的计算与分析

In this paper，based on the Gauss theory of geomagnetism and the spherical harmonic mi}del of the geomagnetic field，the horizontal gradients of the geomagnetic field in north一south and west-;east dlrections were calculated in Chinese and"its surrounding regions, the contour maps of the horizontal gradients of the geomagnetic components were constracted，and its regularities of distributions were analysed.
The horizontal gradients of the total intensity (F)，horizontal intensity (H) and vertical intensity (Z ) vary mainly with lat相似文献   

Lithospheric pressure–depth relationship in compressive regions of thickened crust

We investigate the pressure distribution with depth in regions undergoing horizontal shortening and experiencing crustal thickening both analytically and numerically. Our results show that, in a convergent tectonic setting, pressure can be considerably higher than lithostatic (the pressure resulting from the weight of the overburden). Increases in pressure with respect to lithostatic conditions result from both the contribution of horizontal stresses and the flexural vertical loads, the latter generated by the deflection of the upper crust and of the mantle because of the presence of topographic relief and a root, respectively. The contribution of horizontal stresses is particularly relevant to the upper crust and uppermost mantle, where rocks are thought to deform brittlely. In these domains, pressure gradients twice lithostatic can be achieved. The contribution of horizontal stresses is less important in the ductile domains as differential stresses are progressively relaxed; nevertheless, the effects are still noteworthy especially close to the brittle–ductile transition. Flexural vertical loads generated by the deflection of the upper crust and lithospheric mantle are relevant for rocks of the weaker lower crust. As a result of the combination of the two mechanisms, the pressure gradient varies vertically through the lithosphere, ranging from negative (inverted) gradients to gradients up to several times the lithostatic gradient. The pressure values range from one to two times the lithostatic values (1ρ gz to 2ρ gz ).     

A gradient method for interpreting magnetic anomalies due to horizontal circular cylinders,infinite dykes and vertical steps

A new method of interpreting magnetic anomalies of arbitrarily-magnetised horizontal circular cylinders, dipping dykes and vertical steps is presented. The method makes use of both horizontal and vertical gradients of the magnetic field of the model under consideration, rather than the observed magnetic anomaly. Vertical and horizontal gradients are calculated from the observed anomalies, and plotted one against the other to find out the locus of tip of the resultant gradient vector. This locus is a symmetrical curve for each of the three models mentioned above. The properties of these curves are used to deduce the various parameters of these models and the direction of magnetisation.     

Flow structure of turbidity currents

A two‐dimensional numerical model is used to describe the flow structure of turbidity currents in a vertical plane. To test the accuracy of the model, it is applied to historical flows in Bute Inlet and the Grand Banks flow. The two‐dimensional spatial and temporal distributions of velocity and sediment concentration and non‐dimensionalized vertical profiles of velocity, turbulent kinetic energy and sediment concentration are discussed for several simple computational currents. The flows show a clear interaction between velocity, turbulence and sediment distribution. The results of the numerical tests show that flows with fine‐grained sediment have low vertical and high horizontal gradients of velocity and sediment concentration, show little increase in flow thickness and decelerate slowly. Steadiness and uniformity in these flows are comparable for velocity and concentration. In contrast, flows with coarse‐grained sediment have high vertical and low horizontal velocity gradients and high horizontal concentration gradients. These flows grow considerably in thickness and decelerate rapidly. Steadiness and uniformity in flows with coarse‐grained sediment are different for velocity and concentration. The results show the influence of spatial and temporal flow structure on flow duration and sediment transport.     

潜水回水初始阶段的定性半定量分析及对水跃成因的解释

文章提出并采用水力坡度分析方法,对潜水回水初始阶段进行了定性-半定量分析,为了解潜水回水过程提供了新的视角。通过分析潜水回水初始时刻的水力坡度,河渠侧的界面被分为2段:河间潜水位之上的铅直段和之下的水平段。水平段上点的水力坡度最大且相等,方向为水平向右;铅直段上点的水力坡度方向趋于铅直向下,越向上水力坡度越小。经过微小时间段Δt后,水力坡度均相应变小,铅直段相邻点间地下水运动发生冲突,水力坡度方向由趋于铅直向下向右偏转。将水力坡度分析方法用于分析潜水井流的过程和特征,水跃的成因可解释为:在相同水力坡度和过水断面面积下,井内大空间水流速度远大于孔隙中的潜水流速度,井内水位急速下降,从而形成水跃;水跃越大,进入井内的流量就越大。     

New results on the properties of recent crustal movements in the Bohemian Massif and its boundary with the West Carpathians

Preliminary analysis of the new results of repeated levellings within the territory of the Bohemian Massif and its border with the Carpathians is made, and the correlation between horizontal gradients of vertical movements and main fault zones discussed. The results indicated the continuance of the main movement's tendencies, determined by the foregoing measurements. Also discussed are the vertical and horizontal crustal movements between the Bohemian Massif and the Carpathians. The active zones are connected with the main fault systems, and the horizontal movements indicated the spreading tendencies between both geological structures. These results are in accord with the tendencies of horizontal movements in the Soviet Carpathians.     

A new approach to interpret self-potential anomaly over a two-dimensional inclined sheet using complex gradient analysis

A new approach is developed to determine the model parameters of a two-dimensional inclined sheet from self-potential anomaly. In this method, the numerical horizontal self-potential gradient obtained from self-potential anomaly is convolved using Hilbert transform to obtain the vertical self-potential gradient. The complex gradient is the sum of horizontal and vertical gradient anomalies. The horizontal and vertical gradients are plotted in one graph to form the complex gradient graph. By defining few characteristic points and distances along the complex gradient profile, procedures are then formulated using the analytical functions of the complex gradients to obtain the model parameters of sheet-like structures. The validity of the new proposed method has been tested on synthetic data with and without random noise. The obtained parameters are in congruence with the model parameters when using noise-free synthetic data. After adding 10% random error in the synthetic data, the maximum error in model parameters is 11.8%. Moreover, the method have been applied to analyze and interpret the self-potential anomaly measured on a graphite ore body at southern Bavarian woods, Germany to prove its efficiency where an acceptable agreement has been noticed between the obtained results and the other published results.     

Analysis of gravity gradients over a thin infinite sheet

A simple method to interpret gravity gradients over a thin infinite dipping sheet is discussed. The Hilbert transform is used to compute the vertical gradient from the horizontal gradient of the gravity field. The method is illustrated with a theoretical example.     

太原西山区块煤储层地应力分布特征及评价

地应力是影响煤层气开发的关键参数,为了分析太原西山区块煤储层地应力条件,为煤层气勘探开发提供理论依据,采用水力压裂法测量地应力,统计了太原西山区块35口井煤储层地应力资料,获取二叠系山西组2号煤储层地应力与煤层埋深之间的相关关系,阐明了现今地应力分布特征。结果表明,研究区山西组2号煤层破裂压力梯度、闭合压力梯度和煤储层压力梯度的平均值分别为4.77 MPa/hm、2.82 MPa/hm和0.6 MPa/hm;2号煤层最小水平主应力梯度、最大水平主应力梯度和垂直主应力梯度的平均值分别为2.82 MPa/hm、3.24 MPa/hm和2.7 MPa/hm。主应力均随煤层埋深增加呈线性规律增高。根据最小水平主应力的大小,将研究区划分为低应力区、中应力区、高应力区3个区。      

雄安新区地温场特征及其控制因素

雄安新区地热资源丰富,本文通过对地热井资料的收集分析,并对单井地温梯度值进行计算,结合区域资料,编制本区盖层地温梯度等值线图,并分析了地温梯度值纵横向变化规律及影响因素。本区地温梯度值基本上都在3.0℃/100m以上,局部达到6.0℃/100m;平面上,地温梯度值总体特征是北高南低、中间高两侧低的特点;纵向上,盖层地温梯度值高,热储层内部地温梯度值低;其地温场的变化主要受地质构造、地层岩性、盖层、水文地质条件等因素控制,其中由于地质构造的影响,加上岩石热导率之间的差异,造成来自地幔的热量向上传递过程中重新分配,向背斜核部集中,导致盖层局部地温梯度值高。     

砂砾石与砂接触冲刷试验研究

渗流作用下土层之间的接触面是较易发生渗透破坏的薄弱环节。在开展砂砾石渗透破坏试验研究的基础上,针对砂砾石与砂的接触面渗流及渗透破坏特性,利用大型竖向渗透仪和自主研制的环状径向水平渗透仪,研究了竖向和水平渗流作用下接触面渗流和渗透破坏的影响因素及接触冲刷的发生、发展过程。研究结果表明,典型的砂砾石与砂的接触冲刷破坏过程可分为稳定渗流阶段、过渡阶段和破坏阶段3个阶段,可用2个特征水力坡降进行划分,稳定渗流阶段与过渡阶段的分界点对应的水力坡降称为启动坡降,过渡阶段与破坏阶段的分界点对应的水力坡降称为破坏坡降;砂砾石与砂组合试样的渗透系数随砂砾石密度的增大、颗粒变细而减小,砂砾石与砂接触冲刷的抗渗坡降则随砂砾石密度的增大、颗粒变细而增大,在水平渗流情况下试样的渗透系数较竖向的大,但接触冲刷的抗渗坡降较竖向的小。     

Steady critical discharge rates from vertical and horizontal wells in fresh–saline aquifers with sharp interfaces

In this study, the critical (or maximum) discharge rates before saline water enters a well were determined for vertical and horizontal wells in a freshwater aquifer which is separated from a static saline aquifer by a sharp interface. Flow around the well was solved by integration of a point sink solution along the well axis, and both the critical discharge rate and critical interface rise were determined through a comparison of the heads and vertical gradients at the saline–fresh water interface. The rates were determined for vertical and horizontal wells with various lengths and depths for different aquifer salinities. Results were generalized by drawing dimensionless type curves. The results showed that the dimensionless total critical discharge rates are higher for the longer horizontal wells and longer vertical wells with a certain bottom depth, and they almost linearly decrease with well depth at rates of 0.7–0.9. For the dimensionless well length of 0.2, the dimensionless total discharge rate of a horizontal well is about 0.1 more than that of a vertical well with the same length and well-top depth. Also, the critical discharge rates per unit length of well are inversely proportional to well length and remarkably higher for shallower wells. Additionally, the critical pumping rate is proportional to the salinity difference of the aquifers. These results were confirmed by comparison to existing solutions for vertical wells with dimensionless lengths of 0.2, 0.5 and 0.6, and for critical interface rises in the range of 0.75–0.9.     

低渗透储层水平井—直井联合布井极限注采井距研究

低渗透储层水平井—直井联合布井技术具有广泛的应用前景,其布井方式至关重要。首先利用劈分流场的方法直观地给出常规储层水平井—直井联合布井的产能评价方法;然后针对低渗透储层的渗流特点,在考虑启动压力梯度条件下建立新的井网渗流物理模型并求解得到产能评价公式;最后经分析计算给出启动压力梯度影响的面积井网极限注采井距关系曲线。研究结果为低渗透储层部署水平井—直井联合井网提供理论依据。     

低渗透储层水平井-直井联合布井极限注采井距研究

低渗透储层水平井-直井联合布井技术具有广泛的应用前景,其布井方式至关重要。首先利用劈分流场的方法直观地给出常规储层水平井-直井联合布井的产能评价方法;然后针对低渗透储层的渗流特点,在考虑启动压力梯度条件下建立新的井网渗流物理模型并求解得到产能评价公式;最后经分析计算给出启动压力梯度影响的面积井网极限注采井距关系曲线。研究结果为低渗透储层部署水平井-直井联合井网提供理论依据。     

MuSET: A multiparameter and high precision sensor for downhole spontaneous electrical potential measurements

On the basis of an existing multiparameter borehole fluid sensor (p, T, Cw, pH, Eh), a new downhole tool designed for 200 bars and 75 °C was developed to measure the spontaneous electrical potential in situ with great precision (better than a μV). To this end, the new sensor is based on the use of unpolarizable Pb/PbCl₂ electrodes either at the surface or downhole. In situ testing has demonstrated a capacity to identify several subsurface sources of natural electrical potential such as diffusion ones (membrane potential in the presence of clays, Fickian processes due to pore fluid salinity gradients), or else the electrokinetic mechanisms with gradients in pore fluid pressure. As a consequence, Multi-Sensors Electrical Tool (MuSET) might be used as an “electrical flowmeter” sensitive to both horizontal and vertical fluid flow in a vertical borehole.     

Lidar observation of aerosol stratification in the lower troposphere over Pune during pre-monsoon season of 2006

Lidar observations of aerosol vertical distributions in the lower troposphere along with observations of horizontal and vertical winds from collocated UHF radar (Wind Profiler) over a tropical Indian station, Pune during the pre-monsoon season (March–May) of 2006 as part of an ISRO-GBP national campaign (ICARB) have been examined. Lidar vertical profiles showed high aerosol concentrations in the surface layers and a subsequent gradual decrease with height. Results showed the presence of an elevated stratified aerosol layer around 2000–3500m height which persisted throughout the months of March and April. Observed strong vertical gradients in both horizontal and vertical winds in the lower troposphere seem to be a possible cause for the formation of elevated aerosol layers. Further, high daytime temperatures accompanied by dry conditions at the surface help to enhance the aerosol loading in the lower layers over this location.     

Tephra Fallout Models: The Effect of Different Source Shapes on Isomass Maps

Numerous tephra dispersion and sedimentation models rely on some abstraction of the volcanic plume to simplify forecasts of tephra accumulation as a function of the distance from the volcano. Here we present solutions to the commonly used advection–dispersion equation using a variety of source shapes: a point, horizontal and vertical lines, and a circular disk. These may be related to some volcanic plume structure, such as a strong plume (vertical line), umbrella cloud (circular disk), or co-ignimbrite plume (horizontal line), or can be used to build a more complex plume structure such as a series of circular disks to represent a buoyant weak plume. Basing parameters upon eruption data, we find that depositions for the horizontal source shapes are very similar but differ from the vertical line source deposition. We also compare the deposition from a series of stacked circular disk sources of increasing radius above the volcanic vent with that from a vertical line source.     

运五飞机上航磁梯度测量系统的安装与补偿

介绍了在单阀双翼的运五飞机上安装既可进行垂直梯度测量,又可进行水平梯度测量(包括横向和纵向水平梯度测量)的航磁梯度测量系统的方法,初步探讨应用航空地球物理综合测量系统(AADCⅡ)自动航空磁力数字补偿仪的方法,并对补偿结果进行评价。多次实验结果证明了该补偿方法的效果良好。     

Analysis of gravity gradients over a thin infinite sheet

Expressions are derived for the horizontal and vertical gradients of the gravity anomaly over a thin dipping sheet of infinite depth extent. The resultant of these two gradients, known as the complex gradient, is also derived and properties of the amplitude and phase responses of the complex gradient are studied. It is shown that the amplitude plot is a symmetric curve whose, shape is independent of the dip (?) of the sheet whereas the phase plot is an antisymmetric curve with an offset value equal to ?-π/2. The depth to top of the sheet is obtained from the amplitude plot. The method is applied on a field example and the results are in good agreement with the results obtained by earlier workers.     

Subsystems of RR Lyrae variable stars in our Galaxy

We have used published, high-accuracy, ground-based and satellite proper-motion measurements, a compilation of radial velocities, and photometric distances to compute the spatial velocities and Galactic orbital elements for 174 RR Lyrae (ab) variable stars in the solar neighborhood. The computed orbital elements and published heavy-element abundances are used to study relationships between the chemical, spatial, and kinematic characteristics of nearby RR Lyrae variables. We observe abrupt changes of the spatial and kinematic characteristics at the metallicity [Fe/H]≈?0.95 and also when the residual spatial velocities relative to the LSR cross the critical value V _res≈290 km/s. This provides evidence that the general population of RR Lyrae stars is not uniform and includes at least three subsystems occupying different volumes in the Galaxy. Based on the agreement between typical parameters for corresponding subsystems of RR Lyrae stars and globular clusters, we conclude that metal-rich stars and globular clusters belong to a rapidly rotating and fairly flat, thick-disk subsystem with a large negative vertical metallicity gradient. Objects with larger metal deficiencies can, in turn, be subdivided into two populations, but using different criteria for stars and clusters. We suggest that field stars with velocities below the critical value and clusters with extremely blue horizontal branches form a spherical, slowly rotating subsystem of the protodisk halo, which has a common origin with the thick disk; this subsystem has small but nonzero radial and vertical metallicity gradients. The dimensions of this subsystem, estimated from the apogalactic radii of orbits of field stars, are approximately the same. Field stars displaying more rapid motion and clusters with redder horizontal branches constitute the spheroidal subsystem of the accreted outer halo, which is approximately a factor of three larger in size than the first two subsystems. It has no metallicity gradients; most of its stars have eccentric orbits, many display retrograde motion in the Galaxy, and their ages are comparatively low, supporting the hypothesis that the objects in this subsystem had an extragalactic origin.