Heat flow anomalies and their interpretation

More than 10,000 heat flow determinations exist for the earth and the data set is growing steadily at about 450 observations per year. If heat flow is considered as a surface expression of geothermal processes at depth, the analysis of the data set should reveal properties of those thermal processes. They do, but on a variety of scales. For this review heat flow maps are classified by 4 different horizontal scales of 10ⁿ km (n = 1, 2, 3 and 4) and attention is focussed on the interpretation of anomalies which appear with characteristic dimensions of 10^{(n − 1)} km in the respective representations.The largest scale of 10⁴ km encompasses heat flow on a global scale. Global heat loss is 4 × 10¹³ W and the process of sea floor spreading is the principal agent in delivering much of this heat to the surface. Correspondingly, active ocean ridge systems produce the most prominent heat flow anomalies at this scale with characteristic widths of 10³ km. Shields, with similar dimensions, exhibit negative anomalies.The scale of 10³ km includes continent wide displays. Heat flow patterns at this scale mimic tectonic units which have dimensions of a few times 10² km, although the thermal boundaries between these units are sometimes sharp. Heat flow anomalies at this scale also result from plate tectonic processes, and are associated with arc volcanism, back arc basins, hot spot traces, and continental rifting. There are major controversies about the extent to which these surface thermal provinces reflect upper mantle thermal conditions, and also about the origin and evolution of the thermal state of continental lithosphere.Beginning with map dimensions of 10² km thermal anomalies of scale 10¹ km, which have a definite crustal origin, become apparent. The origin may be tectonic, geologic, or hydrologic. Ten kilometers is a common wavelength of topographic relief which drives many groundwater flow systems producing thermal anomalies. The largest recognized continental geothermal systems have thermal anomalies 10¹ km wide and are capable of producing hundreds of megawatts of thermal energy.The smallest scale addressed in this paper is 10¹ km. Worldwide interest in exploiting geothermal systems has been responsible for a recent accumulation of heat flow data on the smallest of scales considered here. The exploration nature of the surveys involve 10's of drillholes and reveal thermal anomalies having widths of 10⁰ km. These are almost certainly connected to surface and subsurface fluid discharge systems which, in spite of their restricted size, are typically delivering 10 MW of heat to the near surface environment.     

Heat flow maps and deep ground water circulation: Examples from Switzerland

The effect of regional and local ground water circulation systems on the Heat Flow Density (HFD) field is demonstrated by two examples from Switzerland, one near St. Gall in an area at the northern border of the Alps, and the other northwest of Zurich along the eastern end of the Jura mountains. Detailed HFD maps of both areas slow pronounced high heat flow zones which are attributed to discharge of subsurface water which has migrated laterally over several 10 km. Seepage velocities on the order of several mm/yr have been calculated. Geothermal information is not available about the infiltration zones where low HFD values are expected. Geochemical and isotopic analysis of water samples from springs and drillholes indicates the recharge zones and demonstrates the effect of extensive regional systems. These results indicate that in regions with significant topographic relief HFD mapping can be seriously biased if drillholes are positioned in valleys which correspond to discharge areas with relatively high HFD, whereas the low heat flow zones remain undetected.     

环境干扰事件引起的“形变异常变化”

通过对山东泰安台形变观测受抽水、灌溉影响及烟台台形变观测受载荷影响的分析,认为同一台站的多套形变固体潮仪器"同步异常"的出现应成为判定异常发生的重要准则;对同一应变过程不同形变仪器的响应量级会有所不同,分量式应变仪对异常反映最有效,其次是伸缩仪。对几次"干扰异常"所揭示的问题进行了初步讨论,并在形变异常判定科学思路方面提出了一些建议。     

我国断层气测量在地震科学研究中的应用现状

氢气被认为是反应断裂活动最灵敏的地球化学组分之一。研究影响断裂带氢浓度动态变化的主要因素,是科学分析断裂带氢与构造活动关系的基础工作。本文基于河南内乡马山口断层气氢气浓度与辅助测项的连续观测资料,重点分析了氢浓度变化与地温、气温、气压的相关关系,确定了主要影响因素。结果表明,氢气浓度日变化极值介于气温和地温之间,极值点靠近地温一侧。使用逐步回归方法分析进一步证明,地温、温度对氢气浓度均有影响,但地温影响更显著,气压影响不显著。总体来讲,氢浓度会受到地温和气温的双重影响,但与地温关系更为密切。     

Heat flow and ground water flow in the Great Plains of the United States

Regional groundwater flow in deep aquifers adds advective components to the surface heat flow over extensive areas within the Great Plains province. The regional groundwater flow is driven by topographically controlled piezometric surfaces for confined aquifers that recharge either at high elevations on the western edge of the province or from subcrop contacts. The aquifers discharge at lower elevations to the east. The assymetrical geometry for the Denver and Kennedy Basins is such that the surface areas of aquifer recharge are small compared to the areas of discharge. Consequently, positive advective heat flow occurs over most of the province. The advective component of heat flow in the Denver Basin is on the order of 15 mW m⁻² along a zone about 50 km wide that parallels the structure contours of the Dakota aquifer on the eastern margin of the Basin. The advective component of heat flow in the Kennedy Basin is on the order of 20 mW m⁻² and occurs over an extensive area that coincides with the discharge areas of the Madison (Mississippian) and Dakota (Cretaceous) aquifers. Groundwater flow in Paleozoic and Mesozoic aquifers in the Williston Basin causes thermal anomalies that are seen in geothermal gradient data and in oil well temperature data. The pervasive nature of advective heat flow components in the Great Plains tends to mask the heat flow structure of the crust, and only heat flow data from holes drilled into the crystalline basement can be used for tectonic heat flow studies.     

Meanders caused by hyperconcentrated water flow: An example from the loess plateau,China

This paper describes meandering alluvial rivers with mean annual suspended-sediment concentrations of more than 100 kgm^?3 on the Loess Plateau, China, and explains their formation as caused by the effect of hyperconcentrated water flow. When the river is dominated by hyperconcentrated flow, the rate of energy expenditure required for sediment transport declines significantly. Accordingly, the river channel adjusts itself to a lower channel gradient by increasing the river length, resulting in a meandering channel. Since the stable transportation of sediment by hyperconcentrated flow is dependent on river channel boundary conditions, the latter play an important role in the formation of meanders of this kind. The paper also discusses the conditions for the discrimination of meandering and braided rivers in this area.     

梅雨与北极涛动及平流层环流异常的关联

平流层过程如何影响气候变化是一个大家关注的科学问题,在WCRP中专门设置了一个研究子计划SPARC.本文的分析研究表明,中国的梅雨异常可能受到平流层大气环流异常的影响,而这种影响是通过北极涛动（AO）的变化来实现的.从分析和计算结果可以看到,二月份北半球30 hPa位势高度的EOF第一主分量对应着副热带和高纬度地区的显著下传异常波作用量,其第三主分量对应着极地地区的显著下传异常波作用量,这些下传的异常波作用量都对三月份AO形势的形成有明显的贡献.三月份的AO则会通过影响东亚地区夏季对流层大气的冷暖状况和环流,在长江中下游地区导致异常垂直运动和辐散辐合形势,从而影响夏季的梅雨降水.     

Numerically quantifying energy loss caused by squirt flow

In interconnected microcracks, or in microcracks connected to spherical pores, the deformation associated with the passage of mechanical waves can induce fluid flow parallel to the crack walls, which is known as squirt flow. This phenomenon can also occur at larger scales in hydraulically interconnected mesoscopic cracks or fractures. The associated viscous friction causes the waves to experience attenuation and velocity dispersion. We present a simple hydromechanical numerical scheme, based on the interface-coupled Lamé–Navier and Navier–Stokes equations, to simulate squirt flow in the frequency domain. The linearized, quasi-static Navier–Stokes equations describe the laminar flow of a compressible viscous fluid in conduits embedded in a linear elastic solid background described by the quasi-static Lamé–Navier equations. Assuming that the heterogeneous model behaves effectively like a homogeneous viscoelastic medium at a larger spatial scale, the resulting attenuation and stiffness modulus dispersion are computed from spatial averages of the complex-valued, frequency-dependent stress and strain fields. An energy-based approach is implemented to calculate the local contributions to attenuation that, when integrated over the entire model, yield results that are identical to those based on the viscoelastic assumption. In addition to thus validating this assumption, the energy-based approach allows for analyses of the spatial dissipation patterns in squirt flow models. We perform simulations for a series of numerical models to illustrate the viability and versatility of the proposed method. For a 3D model consisting of a spherical crack embedded in a solid background, the characteristic frequency of the resulting P-wave attenuation agrees with that of a corresponding analytical solution, indicating that the dissipative viscous flow problem is appropriately handled in our numerical solution of the linearized, quasi-static Navier–Stokes equations. For 2D models containing either interconnected cracks or cracks connected to a circular pore, the results are compared with those based on Biot's poroelastic equations of consolidation, which are solved through an equivalent approach. Overall, our numerical simulations and the associated analyses demonstrate the suitability of the coupled Lamé–Navier and Navier–Stokes equations and of Biot's equations for quantifying attenuation and dispersion for a range of squirt flow scenarios. These analyses also allow for delineating numerical and physical limitations associated with each set of equations.     

Numerical simulation of ground flow caused by seismic liquefaction

Flow failure of sandy subsoil induced by seismic liquefaction is known to cause significant damage to structures. It is induced not only by the dynamic forces exerted by seismic acceleration but also by the static gravity force in consequence of the topography of the ground. The ground flow may sometimes continue after the end of the seismic loading and finally the ground is significantly deformed to cause a failure.This paper numerically predicts the magnitude of flow that could occur when soil liquefaction continues for a sufficiently long period. It is considered that liquefied soil behaves like a viscous liquid, and hence, ground flow is governed by the principle of minimum potential energy. In the calculation, liquefied sand is assumed to be a viscous liquid that deforms in undrained conditions with its volume remaining constant. To consider the non-linearity due to large displacement, the updated Lagrangian method is used to solve the equation of motion. The Newmark β method is employed to calculate the time history of the ground motion. Finally, a simulation using this calculation method shows that the proposed method gives reasonable results for the conditions indicated.     

Heat flow in Italy

More than fifty heat flow measurements in Italy are examined. The values, corrected only for local influences (when present), are related to the main geological features with the following results: foreland areas, 55±19 mW m^–2, foredeep areas, 45±21 mW m^–2; folded regions and intermountain depressions, 76±29 mW m^–2. In volcanic areas the heat flow rises to in excess of 600 mW m^–2. From a tectonic point of view, these values are consistent with the hypothesis that the Apennine chain is intersected by two arcuate structures: the first from Liguria to Latium is very probably a continental arc, that is an are which occurs within a continent, and the second from Campania to Calabria is very similar from geophysical evidence to the classic island arcs.     

Rapid computation of magnetic anomalies and demagnetization effects caused by bodies of arbitrary shape

Summary With the aid of formulae derived for the field caused by a finite rectangular prism, a machine method is developed for rapid computation of magnetic anomalies due to a body of any shape. Conversely, the method could be utilised for determination of the magnetization vector from the observed anomalies. An example is given to demonstrate the applicability, accuracy and speed of the method. The method is shown to be suitable also for the evaluation of magnetic terrain effects.In addition, a new method is presented which enables high speed calculation of demagnetization effect caused by a body of arbitrary shape where the magnetization in general may be inhomogeneous. Applicability and accuracy of the method are discussed. The method is applied to study the effect of susceptibility on inhomogeneity of the induced magnetization in a cube specimen.For a body of any shape with low susceptibility, a new concept of average demagnetization factor is introduced. Average demagnetization factors so calculated for a cylindrical specimen are tabulated.

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Zusammenfassung Unter Anwendung der Formeln für das Feld eines Quaders wird eine Methode entwickelt um die durch einen Körper beliebiger Form erzeugten magnetischen Anomalien mit Hilfe eines Rechenautomaten zu berechnen. Umgekehrt kann die Methode verwendet werden, um aus den beobachteten Anomalien den Magnetisierungsvektor zu bestimmen. An einem Beispiel wird die Anwendbarkeit, die Genauigkeit und die Schnelligkeit der Methode erläutert. Die Methode kann auch für die Berechnung von magnetischen Terraineffekten verwendet werden.Zudem wird eine neue Methode dargelegt, welche eine rasche Berechnung des Entmagnetisierungseffektes eines Körpers beliebiger Gestalt und inhomogener Magnetisierung ermöglicht. Anwendbarkeit und Genauigkeit der Methode werden besprochen. Die Methode wurde verwendet, um den Einfluss der Suszeptibilität auf die Inhomogenität der induzierten Magnetisierung in einem Würfel zu untersuchen.Für Körper beliebiger Form mit kleiner Suszeptibilität wls neuer Begriff der mittlere Entmagnetisierungsfaktor eingeführt. Mittlere Entmagnetisierungsfaktoren für eine zylindrische Probe werden tabelliert.

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Part I of the dissertation Theretical study of the magnetic attraction due to rock bodies and experimental investigation of the stability of rock magnetism submitted to the Swiss Federal Institute of Technology (ETH), Zurich, for the degree of Doctor of Natural Sciences.     

Robust inversion analysis of local gravity anomalies caused by geological dislocation model of faults

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Heat flow and ground water movement in the Bohemian cretaceous basin (Czechoslovakia)

Sub-surface temperature fields may be considerably affected by active ground water systems, thereby seriously hampering the interpretation of heat flow data. Quantitative evaluation of the convective component of heat transfer is thus very important in cases such as large sedimentary basins with vast underground water circulation. We propose in this study a simple model of horizontal aquifer. This model was used to examine the effect of the lateral convection on the surface heat flow near the recharge zone of basinal margins. The perturbation of the heat flow field above the aquifer was calculated for various aquifer geometry and various flow velocities and the regional scale dependence of the perturbation on the hydraulic properties of the aquifer was demonstrated. The model was applied to the Bohemian Cretaceous Basin and it was shown that within a few kilometres from the recharge zones the observed surface heat flow may be underestimated by up to several tens of percent. The procedure was tested in two locations in this area, in an attempt to make hydrogeological corrections to the measured heat flow values in several boreholes.     

On water circulation in Tatar Strait

Numerical modeling with the help of an oceanic model developed in the Bergen University and with mean annual data was used to carry out monthly calculations of water circulation fields in Tatar Strait, to calculate the vertical velocities and horizontal transfer rates between three areas identified within the strait and on its external boundaries. Analysis of calculation results revealed new features in water circulation in the strait (in particular, in winter) and made it possible, for the first time, to jointly evaluate water exchange components on the external boundaries and within the strait.     

Computation of gravity anomalies caused by three-dimensional bodies of arbitrary shape and arbitrary varying density

Summary A numerical method is proposed which enables a direct computation of the vertical gravity anomaly due to three-dimensional bodies of arbitrary shape and with an inhomogeneous density distribution. The bodies are approximated by an assembly of appropriate curved finite elements. Gravity effects of such elements are calculated using the Gaussian quadrature formula. The integration domain is simply a cube, into which all the finite elements are transformed. The accuracy of the method is tested on a numerical example.     

扰动位能与大气环流异常的耦合关系及机理研究

本文在前期局地扰动位能理论工作基础上,进一步着眼于扰动位能与大气环流异常的关系和机理问题,采用奇异值分解(SVD)方法分析了扰动位能与高、中、低层大气动能的耦合相关模态以及年际变率情况,同时考察它与作为大气质量分布的海平面气压之间的相关关系,并从物理上初步探讨了扰动位能与大气动能以及质量的相关机理问题.结果表明,扰动位能自身变率的第一模态同时也是与大气环流异常场耦合变化的主要模态,与之相对应的大气动能和质量场的主模态也是其自身变率的支配模态,说明它们之间存在相互制约的物理机制.而且,热带外地区大气环流主模态特征的形成,与扰动位能兼具全球尺度纬向对称结构和局地尺度纬向非对称性密不可分.另外,冬季南北半球环状模指数与扰动位能的前两阶矩存在非常好的相关关系,而在夏季这种关系明显削弱,仅存在于南半球.     

Heat flow at standard depth

Secular and long-term periodic changes in surface temperature cause perturbations to the geothermal gradient which may be significant to depths of at least 1000 m, and major corrections are required to determine absolute values of heat flow from the Earth's interior. However, detailed climatic models remain contentious and estimates of error in geothermal gradients differ widely. Consequently, regions of anomalous heat flow which could contain geothermal resources may be more easily resolved by measuring relative values at a standard depth (e.g. 100 m) so that all data are subject to similar corrections.Regional heat flow data obtained in existing deep holes show reasonable correlation with values determined at shallow depth. Hence geothermal resources of low enthalpy can be characterised by extrapolating temperatures from relative heat flow data readily obtained from shallow boreholes. Regional control can be provided by casing deep boreholes drilled for other purposes.For routine geothermal exploration, borehole temperatures can be measured using gradient probes with fixed sensor separation (e.g. 5 m), allowing very accurate determinations of the geothermal gradient at a single depth. Values of relative heat flow can then be obtained after determining the thermal resistivity of the corresponding core interval. Sampling errors can be minimised by multiple determinations of thermal conductivity over the complete interval.     

On the interpretation of near-bottom water temperature anomalies

A positive water temperature anomaly of 0.11°C and an inverse gradient of potential temperature of 1.5 × 10^?2°C/m has been measured at the TAG hydrothermal field in the rift valley of the Mid-Atlantic Ridge at latitude 26°N by means of a thermistor array towed between 2 and 20 m above the seafloor. This anomaly appears to be associated with hydrothermal discharge from the oceanic crust. The temperature data are interpreted in terms of (1) a steady, turbulent thermal plume rising in a homogeneous, neutrally buoyant medium, and (2) turbulent diffusion in the ocean-bottom boundary layer. The calculations indicate that the thermal output of the TAG anomaly area is of the order of several megawatts, which is of the same order of magnitude as some continental geothermal systems. The thermal output from the TAG anomaly area represents a significant fraction of the total heat loss resulting from the generation of new lithosphere at the Mid-Atlantic Ridge at 26°N.     

全球水质量迁移对海平面空间模式周年变化的影响

大气、陆地水和海洋之间的水质量迁移对海平面的影响一般假定为均匀薄层分布.但实际上,水质量负荷重新分布一方面会使地壳产生形变,另一方面会引起重力位势场变化(引力位和离心力位),这都会对海平面时空变化特征产生影响,两方面之和称为负荷自吸引效应(SAL).海洋模式模拟的时变洋底压力结果一般符合Boussinesq假设即体积守恒,忽略了大气、陆地水和海洋之间水质量交换的影响.本文基于海平面变化方程,联合陆地水模型、大气地表气压模型、海洋洋底压力模型和GRACE反演的冰川质量变化,详细讨论了2003-2010年SAL对海平面周年变化的影响.主要结论有:(1)SAL对全球海平面周年变化有显著影响,振幅在1.3~19 mm.其中近海岸和低纬度区域受影响较大.(2)在SAL引起的海平面周年振幅变化的因素中,陆地水储量变化因素最大,大气因素次之,非潮汐海洋影响最小.但非潮汐海洋对海平面周年相位空间变化的影响最为复杂.(3)通过与国际长期验潮站观测数据结果比较,在ECCO海洋模式估计的洋底压力结果中引入SAL,能多解释约5.3%观测信号方差.     

Plutonium and210Pb distributions in northeast Atlantic sediments: subsurface anomalies caused by non-local mixing

The depth distributions of²¹⁰Pb and^239,240Pu measured in a suite of box cores collected from water depths of 4000–5000 m in the northeast Atlantic Ocean exhibit pronounced subsurface maxima caused by sediment reworking by benthic infauna. Small-scale spatial heterogeneity in bioturbation rates is indicated by large differences in tracer profiles from duplicate cores separated only by a few centimeters.²¹⁰Pb and^239,240Pu activity distributions from each subcore exhibit a high degree of correlation, and most tracer profiles exhibit one or more subsurface maxima.One-dimensional, “biodiffusion” analogue models do not adequately simulate the principal features of this data set. However, an inverse “conveyer belt” mixing model which simulates subsurface egestion (or a functionally equivalent process) of surficial material which is enriched both in organic debris and radioactive tracers can reproduce the subsurface tracer maxima. Single-event and continuous subsurface egestion models have been formulated and solved for different “feeding rates” and background biodiffusive fields. The single-event model provides a better fit to the data and, in particular, ensures the observed, high degree of correlation between the²¹⁰Pb and^239,240Pu activity profiles, regardless of the different tracer input functions. The most likely candidate responsible for subsurface tracer egestion is a large infaunal worm of the phylum Sipunculida which dominates the biomass below a depth of 3 cm.