A land surface model incorporated with soil freeze/thaw and its application in GAME/Tibet

Land surface process is of great importance in global climate change, moisture and heat exchange in the interface of the earth and atmosphere, human impacts on the environment and eco- system, etc. Soil freeze/thaw plays an important role in cold land surface processes. In this work the diurnal freeze/thaw effects on energy partition in the context of GAME/Tibet are studied. A sophisti- cated land surface model is developed, the particular aspect of which is its physical consideration of soil freeze/thaw and vapor flux. The simultaneous water and heat transfer soil sub-model not only reflects the water flow from unfrozen zone to frozen fringe in freezing/thawing soil, but also demon- strates the change of moisture and temperature field induced by vapor flux from high temperature zone to low temperature zone, which makes the model applicable for various circumstances. The modified Picard numerical method is employed to help with the water balance and convergence of the numerical scheme. Finally, the model is applied to analyze the diurnal energy and water cycle char- acteristics over the Tibetan Plateau using the Game/Tibet datasets observed in May and July of 1998. Heat and energy transfer simulation shows that: (i) There exists a negative feedback mechanism between soil freeze/thaw and soil temperature/ground heat flux; (ii) during freezing period all three heat fluxes do not vary apparently, in spite of the fact that the negative soil temperature is higher than that not considering soil freeze; (iii) during thawing period, ground heat flux increases, and sensible heat flux decreases, but latent heat flux does not change much; and (iv) during freezing period, soil temperature decreases, though ground heat flux increases.     

Formation of the thermal-driven boundary jet in an f-plane mesoscale basin

The paper adopts an f-plane quasi-geostrophic inertial model without linearization to investigate the perturbation temperature, boundary jet and upwelling (downwelling) in an idealized rectangular basin, under the consideration of west side friction layer and heat conservation. There is net heat input on the upper surface and equal quality heat dissipation on the west boundary, and without heat exchange on other boundaries, then the heat is conservation in the whole basin. Results show that there is thermal front due to denseness of the perturbation temperature in the west side boundary, the perturbation pressure and flow field are reversal on the upper layer and bottom layer. On the bottom layer, the west coastal current is northward, and the maximum perturbation pressure center is on the west, however, on the upper layer, the east coastal current is southward, and the maximum perturbation pressure center is on the east. There is strong vertical flow in narrow western boundary layer, and also in the central zone. The effect of different upper thermal forcings is also studied, and it can be concluded that there is always temperature denseness and boundary jet near the west boundary, and the appearance of flow field reversal, but the distribution of vertical flow is rather different.     

Research Progress on the Problem of Fluid,Heat and Energy Distribution near the Earthquake Source Area

As the basic problems in seismology, fluid, heat and energy distribution near earthquake sources during earthquake generation have been the leading subjects of concern to seismologists. Currently, more and more research shows fluid around earthquake source areas, which plays an important role in the process of earthquake preparation and generation. However, there is considerable controversy over the source of fluid in the deep crust. As for the problem of heat around earthquake source areas, different models have been proposed to explain the stress heat flow paradox. Among them, the dynamic weakening model has been thought to be the key to solving the heat flow paradox issue. After large earthquakes, energy distribution is directly related to friction heat. It is of timely and important practical significance to immediately implement deep drilling in-site surveying to gain understanding of fluid, friction heat and energy distribution during earthquake generation. The latest international progress in fluid, heat and energy distribution research has been reviewed in this paper which will bring important inspiration for the understanding of earthquake preparation and occurrence.     

基于BISQ模型的三维双相各向异性介质数值模拟

Biot-flow and squirt-flow are the two most important fluid flow mechanisms in porous media containing fluids. Based on the BISQ （Biot-Squirt） model where the two mechanisms are treated simultaneously, the elastic wave-field simulation in the porous medium is limited to two-dimensions and two-components （2D2C） or two-dimensions and three-components （2D3C）. There is no previous report on wave simulation in three- dimensions and three-components. Only through three dimensional numerical simulations can we have an overall understanding of wave field coupling relations and the spatial distribution characteristics between the solid and fluid phases in the dual-phase anisotropic medium. In this paper, based on the BISQ equation, we present elastic wave propagation in a three dimensional dual-phase anisotropic medium simulated by the staggered-grid high-order finite-difference method. We analyze the resulting wave fields and show that the results are an improvement.     

天然气水合物似海底反射层(BSR)AVA特征:双相介质模型

The bottom simulating reflector （BSR） in gas hydrate-bearing sediments is a physical interface which is composed of solid, gas, and liquid and is influenced by temperature and pressure. Deep sea floor sediment is a porous, unconsolidated, fluid saturated media. Therefore, the reflection and transmission coefficients computed by the Zoeppritz equation based on elastic media do not match reality. In this paper, a two-phase media model is applied to study the reflection and transmission at the bottom simulating reflector in order to find an accurate wave propagation energy distribution and the relationship between reflection and transmission and fluid saturation on the BSR. The numerical experiments show that the type I compressional （fast） and shear waves are not sensitive to frequency variation and the velocities change slowly over the whole frequency range. However, type II compressional （slow） waves are more sensitive to frequency variation and the velocities change over a large range. We find that reflection and transmission coefficients change with the amount of hydrate and free gas. Frequency, pore fluid saturation, and incident angle have different impacts on the reflection and transmission coefficients. We can use these characteristics to estimate gas hydrate saturation or detect lithological variations in the gas hydrate-bearing sediments.     

Effect of opening the Drake Passage on the oceanic general circulation:A box model study

The impacts of opening the Drake Passage(DP) on the oceanic general circulation are examined.When the DP is open,wind stress at mid-and high latitudes gives rise to a wind-driven gyre,which induces a meridional heat exchange between mid-and high latitudes in the Southern Ocean.After the opening of the DP,the Antarctic Circumpolar Current(ACC) forms and its associated strong temperature front blocks the heat transport from mid-latitudes to high latitudes.A simple box model is formulated,in which the effects of the wind stress(for the case of DP closed) and the thermal front(for the case of DP open) on the variability of Antarctic Bottom Water(AABW) and North Atlantic Deep Water(NADW) are explored.The sensitivity experiments demonstrate that:(1) When the DP is closed,the enhancement of the wind-driven gyre leads to the decline of AABW formation in the Southern Ocean and the increase of NADW formation in the North Atlantic.As a result,water in high latitudes of the Southern Ocean becomes warmer,so does the bottom water of global ocean.(2) When the DP is open,there is no formation of AABW until the intensity of thermal front along ACC exceeds a threshold value(it is 4.03℃ in our model).Before the formation of AABW,temperature in most of the oceans is higher than that after the formation of AABW,which usually leads to the cooling of high latitudes of the Southern Hemisphere and the bottom water in global ocean.When the strength of the thermal front is lower than the critical value,there is no AABW formation,and temperature in most of the oceans is slightly higher.These results demonstrate that during the opening of the DP,changes in wind stress and the formation of the thermal front in the Southern Ocean can substantially affect the formation of AABW and NADW,thus changing the state of meridional overturning circulation in the global ocean.     

Application on Anomaly Detection of Geoelectric Field Based on Deep Learning

The deep learning method has made nurnerials achievements regarding anomaly detection in the field of time series. We introduce the speech production model in the field of artificial intelligence, changing the convolution layer of the general convolution neural network to the residual element structure by adding identity mapping, and expanding the receptive domain of the model by using the dilated causal convolution. Based on the dilated causal convolution network and the method of log probability density function, the anomalous events are detected according to the anomaly scores. The validity of the method is verified by the simulation data, which is applied to the actual observed data on the observation staion of Pingliang geoeletric field in Gansu Province. The results show that one month before the Wenchuan M_S8.0, Lushan M_S7.0 and Minxian-Zhangxian M_S6.6 earthquakes, the daily cumulative error of log probability density of the predicted results in Pingliang Station suddenly decreases, which is consistent with the actual earthquake anomalies in a certain time range. After analyzing the combined factors including the spatial electromagnetic environment and the variation of micro fissures before the earthquake, we explain the possible causes of the anomalies in the geoelectric field of before the earthquake. The successful application of deep learning in observed data of the geoelectric field may behefit for improving the ultilization rate both the data and the efficiency of detection. Besides, it may provide technical support for more seismic research.     

BASEMENT WEAKNESS ZONES ON NORTH CHINA PLATFORM AND ITS RELATIONSHIP WITH SEISMIC ACTIVITY

Based on the analysis of the formation and evolution of the crystalline basement for the North China platform, the characteristics of huge ductile shear zone are studied. The zone in point were formed during the early Proterozoic time and can be subdivided into three systems trending northeast, with a width va-ring from saveral hundred meters to more than twenty kilometres, strenching for some thousand kilometres. Along these zone reworked gneiss and mylonite have been commonly developed.The relationship between the successive activition of major basement weakness zones that occurred later on and seismic activities is discussed here along with the general trend of recent adjustment of displacements and regular seismic activities     

The Geothermal Study of the Mid-Segment of the Tancheng-Lujiang Fault Zone and Its Neighboring Region

In this paper,25 new terrestrial heat flow values newly observed along the mid-segment of the Tancheng-Lujiang fault zone are listed.With these geothermal data and 37 other terrestrial heat flow values(previously published),we describe the distribution features of terrestrial heat flows in the area.In this research,the two-dimensional temperature structure from the surface to lithospheric bottom of the Huaibei-Sixian-Jinhu profile is inferred by using the finite-element method and the temperature and heat flow of sedimentary,granitic,and basaltic layers is calculated.     

注水井温度场模型及其数值模拟研究

油田注水开发中后期,井温测井在常规注水工艺的条件下,难以准确地反映注水剖面的实际情况．为此,本文根据注水井井筒与地层的传热机理,针对注水井多层注入的实际情况,建立了井筒及其周围地层的温度场数学模型．用该模型模拟计算了大庆油田某注水井的井下温度场分布,计算结果与实测结果接近,说明模型是适用的．通过对不同注入条件和地质条件的数值模拟,得出注水温度同井眼温度差别越大或注水速度越快,井温曲线越易于识别注入剖面．同时,对如何改善注水工艺,以提高井温测井识别注入剖面的能力提出了合理化建议．     

注聚合物井井下温度分布数值模拟研究

本文提出了一种计算注聚合物井井下温度分布的方法,该方法视井筒内的聚合物溶液为非牛顿幂律流体,考虑注入流体在井筒中同一截面上的速度变化,根据聚合物溶液在多孔介质中的流变性,依据广义达西定律求取渗流速度,基于能量守恒方程建立柱坐标系下注聚合物井井筒内流体、注入层及围岩的二维温度场模型.通过合理的边界条件,将三部分模型耦合起来,采用交替方向半隐式有限差分法求解建立的井下温度场模型.考查了注入量、注入时间、幂律指数和稠度系数、注入液温度等因素对井下温度场分布的影响,结果表明,当注入的聚合物溶液温度低于注入层的原始温度时,随注入量和注入时间的增大以及粘度的减小,注入层的温度降低;注入聚合物溶液温度与注入层原始温度差越大,注入层处的温度剖面异常越明显.本文数值计算结果可用于指导注聚合物井的井温测井应用.     

A novel analytical solution for a slug test conducted in a well with a finite-thickness skin

An aquifer containing a skin zone is considered as a two-zone system. A mathematical model describing the head distribution is presented for a slug test performed in a two-zone confined aquifer system. A closed-form solution for the model is derived by Laplace transforms and Bromwich integral. This new solution is used to investigate the effects of skin type, skin thickness, and the contrast of skin transmissivity to formation transmissivity on the distributions of dimensionless hydraulic head. The results indicate that the effect of skin type is marked if the slug-test data is obtained from a radial two-zone aquifer system. The dimensionless well water level increases with the dimensionless positive skin thickness and decreases as the dimensionless negative skin thickness increases. In addition, the distribution of dimensionless well water level due to the slug test depends on the hydraulic properties of both the wellbore skin and formation zones.     

Large amount of fluid migration around shallow seismogenic depth preserved in tectonic mélange: Yokonami mélange,the Cretaceous Shimanto Belt,Kochi, Southwest Japan

Studying subduction zone fluid at shallow seismogenic depths is important to understand the nature of fault rocks at the updip limit of the seismogenic zone because fluid–rock interactions affect heat and mass transfer, and fault strength. In this study, we conducted detailed analyses of distribution of shear veins, and estimation of pressure–temperature conditions for shear vein formation for the Yokonami mélange, Shikoku, Southwest Japan, which is tectonic mélange zone in an on‐land accretionary complex. We found a seismogenic fault at the upper boundary of the Yokonami mélange, indicating that the Yokonami mélange was active at seismogenic depth. The field‐transect distribution of shear veins was examined. The frequency, the total and mean thicknesses of the shear veins were about 3.7 per meter, about 10 mm per meter, and about 3 mm per shear vein, respectively. Quartz within the shear veins shows elongate‐blocky textures, suggesting precipitation from advective flow. The pressure and temperature conditions for shear vein formation were examined by fluid inclusion analysis, ranging 175–225°C and 143–215 MPa, respectively. The temperature is almost consistent with the paleotemperature determined from vitrinite reflectance, suggesting that the shear veins were formed at up to the maximum depth. The depth might be consistent with that where the seismogenic fault was formed. On the basis of the pressure and temperature conditions and the distribution of shear veins, we estimated the minimum volumetric ratio of fluid to host rocks, assuming that the shear veins had precipitated from advective flow. The estimated amount of fluid is about 106 m³ per cubic meter of host rocks. The results suggest that a large amount of fluid migrates through mélange zones at shallow seismogenic depths. This fluid possibly originates from the dehydration of clay minerals from underthrusted sediments and an altered subducting slab.     

DOWNHOLE PERIODIC SEISMIC SOURCES*

Downhole periodic seismic sources have been proposed as a means for studying fluid zones in hydrothermal/magma systems encountered in deep scientific holes drilled as part of the Continental Scientific Drilling Program. Scientific measurements in these holes will require the use of downhole, nondestructive, high resolution, seismic tools. Downhole periodic seismic sources tested in a shallow geothermal zone showed that a pneumatic oscillator could effectively generate downhole low-frequency (10–100 Hz) seismic waves and that these waves could effectively penetrate a highly fractured formation. An improved version of these downhole sources, capable of swept-frequency operation, is currently under development. This type of downhole seismic source has applications in crustal studies and in the evaluation of petroleum, groundwater and geothermal reservoirs.     

TWO DIMENSIONAL MODEL ON RELATION BETWEEN THERMAL ANOMALY BEFORE WENCHUAN EARTHQUAKE AND TECTONIC STRESS

It has been reported that there is thermal anomaly within a certain time and space preceding an earthquake, and previous research has indicated potential associations between the thermal anomaly and earthquake faults, but it is still controversial whether physical processes associated with seismic faults can produce observable heat.Based on rock experiments, some scholars believe that the convective and stress-induced heat associated with fault stress changes may be the cause of those anomalies. Then, did the thermal anomaly before the Wenchuan earthquake induced by the fault stress change?It remains to be tested by numerical simulations on the distribution and intensity of thermal anomalies. For example, is the area of thermal anomaly caused by the fault stress changes before the earthquake the same as the observation?Is the intensity the same?To clarify the above questions, a two-dimensional thermo-hydro-mechanical(THM)finite element model was conducted in this study to simulate the spatial and temporal variations of thermal anomalies caused by the underground fluid convection and rock stress change due to the tectonic stress release on fault before earthquake. Results showed that the simulated thermal anomalies could be consistent with the observed in magnitude and spatio-temporal distribution. Before the Wenchuan earthquake, deformation-related thermal anomalies occurred mainly in the fault zone and its adjacent hanging wall, which are usually abnormal temperature rise, and occasionally abnormal cooling, occurring in the fault zone after the peak temperature rise. In the fault zone, the thermal anomaly is usually greater than the order of 1K of the equivalent air temperature and is controlled by the combined effect of fluid convection and stress change. The temperature increases first and then decreases before the earthquake. In the hanging wall, it's weaker than that of the fault zone, mainly depending on the convection of the fluid. The temperature gradually increases before the earthquake and is dramatically affected by the permeability. Usually, only when the permeability is larger than 10^-13m², can the air temperature rise higher than 1K occur. The results of this study support the view that fluid convection and stress change caused by fault slip before the earthquake can produce observable air temperature anomalies.     

A mathematical model for 2D heat transfer dynamics in fluid systems with localized sink of magmatic fluid into local fractured zones above the top of crystallizing intrusions

A model describing two-dimensional (2D) dynamics of heat transfer in the fluid systems with a localized sink of a magmatic fluid into local fractured zones above the roof of crystallizing crustal intrusions is suggested. Numerical modeling of the migration of the phase boundaries in 2D intrusive chambers under retrograde boiling of magma with relatively high initial water content in the melt shows that, depending on the character of heat dissipation from a magmatic fluid into the host rock, two types of fluid magmatic systems can arise. (1) At high heat losses, the zoning of fluidogenic ore formation is determined by the changes in temperature of the rocks within the contact aureole of the intrusive bodies. These temperature variations are controlled by the migration of the phase boundaries in the cooling melt towards the center of the magmatic bodies from their contacts. (2) In the case of a localized sink of the magmatic fluid in different parts of the top of the intrusive chambers, a specific characteristic scenario of cooling of the magmatic bodies is probably implemented. In 2D systems with a heat transfer coefficient ?? _k < 5 × 10⁴ W/m² K, an area with quasi-stationary phase boundaries develops close to the region of fluid drainage through the fractured zone in the intrusion. Therefore, as the phase boundaries contract to the sink zone of a fluid, specific thermal tubes arise, whose characteristics depend on the width of the fluid-conductive zone and the heat losses into the side rocks. (3) The time required for the intrusion to solidify varies depending on the particular position of the fluid conductor above the top of the magmatic body.     

同井不同层位水温观测同震变化机理分析

不同水温观测点由于观测环境、井孔条件、观测部位构造条件、介质条件、地下水动力条件的差异,使得水温动态呈现出不同的形态。而同一观测井内不同层位的水温由于水温传感器安置深度和井孔热源分布状态的不同,会出现不同的同震响应形态。利用小波变换算法,分析了房县三海村井不同深度的水温在3次地震中的同震响应变化,并结合该井的温度梯度、围岩特性以及含水层分布,提出一个简单的井-含水层模型。进而探讨了同井不同层位水温出现不同变化的动力学机制,初步认为其动力学机制源于水的流动产生的热对流引起的变化。     

Radial groundwater flow to a finite diameter well in a leaky confined aquifer with a finite‐thickness skin

A mathematical model that describes the drawdown due to constant pumpage from a finite radius well in a two‐zone leaky confined aquifer system is presented. The aquifer system is overlain by an aquitard and underlain by an impermeable formation. A skin zone of constant thickness exists around the wellbore. A general solution to a two‐zone leaky confined aquifer system in Laplace domain is developed and inverted numerically to the time‐domain solution using the modified Crump (1976) algorithm. The results show that the drawdown distribution is significantly influenced by the properties and thickness of the skin zone and aquitard. The sensitivity analyses of parameters of the aquifer and aquitard are performed to illustrate their effects on drawdowns in a two‐zone leaky confined aquifer system. For the negative‐skin case, the drawdown is very sensitive to the relative change in the formation transmissivity. For the positive‐skin case, the drawdown is also sensitive to the relative changes in the skin thickness, and both the skin and formation transmissivities over the entire pumping period and the well radius and formation storage coefficient at early pumping time. Copyright © 2009 John Wiley & Sons, Ltd.