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1.
Shear wave anisotropy in the crust around the San Andreas fault near Parkfield: spatial and temporal analysis 总被引：1，自引：0，他引：1
We systematically analysed shear wave splitting (SWS) for seismic data observed at a temporary array and two permanent networks around the San Andreas Fault (SAF) Observatory at Depth. The purpose was to investigate the spatial distribution of crustal shear wave anisotropy around the SAF in this segment and its temporal behaviour in relation to the occurrence of the 2004 Parkfield M 6.0 earthquake. The dense coverage of the networks, the accurate locations of earthquakes and the high-resolution velocity model provide a unique opportunity to investigate anisotropy in detail around the SAF zone. The results show that the primary fast polarization directions (PDs) in the region including the SAF zone and the northeast side of the fault are NW–SE, nearly parallel or subparallel to the SAF strike. Some measurements on the southwest side of the fault are oriented to the NNE–SSW direction, approximately parallel to the direction of local maximum horizontal compressive stress. There are also a few areas in which the observed fast PDs do not fit into this general pattern. The strong spatial variations in both the measured fast PDs and time delays reveal the extreme complexity of shear wave anisotropy in the area. The top 2–3 km of the crust appears to contribute the most to the observed time delays; however substantial anisotropy could extend to as deep as 7–8 km in the region. The average time delay in the region is about 0.06 s. We also analysed temporal patterns of SWS parameters in a nearly 4-yr period around the 2004 Parkfield main shock based on similar events. The results show that there are no appreciable precursory, coseismic, or post-seismic temporal changes of SWS in a region near the rupture of an M 6.0 earthquake, about 15 km away from its epicentre. 相似文献
2.
Summary. The polarizations of shear waves recorded by networks of digital three-component seismometers immediately above small earthquakes near the North Anatolian Fault in Turkey display shear-wave splitting on almost all shear-wave seismograms recorded within the shear-wave window. This splitting is incompatible with source radiation-patterns propagating through simple isotropic structures but is compatible with effective anisotropy of the internal structure of the rock along the ray paths. This paper interprets the phenomena in terms of widespread crack-induced anisotropy. Distributions of stress-induced cracks model many features of the observations, and synthetic polarization diagrams calculated for propagation through simulated cracked rock are similar to the observed patterns. This evidence for widespread crack-induced anisotropy lends strong support to the hypothesis of extensive-dilatancy anisotropy (EDA) suggested by laboratory experiments in subcritical crack-growth. The crucial evidence confirming some form of EDA would be observations of temporal changes in shear-wave splitting as the stress field alters the crack density and crack geometry. There is some weak evidence for such temporal changes at one site, but further analysis of suitable digital three-component seismometer networks in seismic areas is required to confirm EDA. 相似文献
3.
GIMMS NDVI database and geo-statistics were used to depict the spatial distribution and temporal stability of NDVI on the Mongolian Plateau.The results demonstrated that:(1) Regions of interest with high NDVI indices were distributed primarily in forested mountainous regions of the east and the north,areas with low NDVI indices were primarily distributed in the Gobi desert regions of the west and the southwest,and areas with moderate NDVI values were mainly distributed in a middle steppe strap from northwest to southeast.(2) The maximum NDVI values maintained for the past 22 years showed little variation.The average NDVI variance coefficient for the 22-year period was 15.2%.(3) NDVI distribution and vegetation cover showed spatial autocorrelations on a global scale.NDVI patterns from the vegetation cover also demonstrated anisotropy;a higher positive spatial correlation was indicated in a NW-SE direction,which suggested that vegetation cover in a NW-SE direction maintained increased integrity,and vegetation assemblage was mainly distributed in the same specific direction.(4) The NDVI spatial distribution was mainly controlled by structural factors,88.7% of the total spatial variation was influenced by structural and 11.3% by random factors.And the global autocorrelation distance was 1178 km,and the average vegetation patch length(NW-SE) to width(NE-SW) ratio was approximately 2.4:1.0. 相似文献
4.
蒙古高原NDVI的空间格局及分异 总被引：5，自引：2，他引：3
GIMMS NDVI database and geo-statistics were used to depict the spatial distribu-tion and temporal stability of NDVI on the Mongolian Plateau. The results demonstrated that: (1) Regions of interest with high NDVI indices were distributed primarily in forested moun-tainous regions of the east and the north, areas with low NDVI indices were primarily distrib-uted in the Gobi desert regions of the west and the southwest, and areas with moderate NDVI values were mainly distributed in a middle steppe strap from northwest to southeast. (2) The maximum NDVI values maintained for the past 22 years showed little variation. The average NDVI variance coefficient for the 22-year period was 15.2%. (3) NDVI distribution and vege-tation cover showed spatial autocorrelations on a global scale. NDVI patterns from the vegetation cover also demonstrated anisotropy; a higher positive spatial correlation was in-dicated in a NW-SE direction, which suggested that vegetation cover in a NW-SE direction maintained increased integrity, and vegetation assemblage was mainly distributed in the same specific direction. (4) The NDVl spatial distribution was mainly controlled by structural factors, 88.7% of the total spatial variation was influenced by structural and 11.3% by random factors. And the global autocorrelation distance was 1178 km, and the average vegetation patch length (NW-SE) to width (NE-SW) ratio was approximately 2.4:1.0. 相似文献
5.
P. N. J. Rasolofosaon W. Rabbel S. Siegesmund & A. Vollbrecht 《Geophysical Journal International》2000,141(2):413-424
We analyse the relation between rock fabric, expressed by the preferred orientation of rock-forming minerals and microcracks, and elastic anisotropy of crystalline rock from the KTB pilot well. Detailed analyses of mineralogical composition, textures and microcrack fabrics were performed. In addition, ultrasonic velocity measurements of spherical samples in several directions were carried out at various confining pressures, and inverted in terms of the complete set of 21 elastic constants. By comparing the elastic tensors of the rocks at the final confining pressure (at which most of the microcracks are closed) with those at a lower pressure level, it is possible to separate the anisotropy induced by microcracks from that caused by mineral alignment. In contrast to previous work, no a priori knowledge of the type of anisotropy (triclinic, monoclinic, orthotropic etc.), or of the spatial orientation of the symmetry elements (planes, axes) of the cracked rock or of the intact rock is assumed. Furthermore, no restrictive assumptions on the orientation distribution function and the shape of the cracks are needed.
The results show that the elastic anisotropy characteristics, whether they are related to the microcracks or to the rock-forming minerals, are clearly correlated with the directly observed rock fabrics. We show that the symmetry directions of the mineral fabric and of microcrack fabric agree. A further result is that the microcrack-induced anisotropy dominates the other causes of anisotropy at confining pressures smaller than a few tens of megapascals, the situation being reversed at higher pressures. The laboratory data are quantitatively compared with sonic log data from the KTB well, showing the influence of pore fluids, effective pressure and crack density reduction on the anisotropy in situ . 相似文献
The results show that the elastic anisotropy characteristics, whether they are related to the microcracks or to the rock-forming minerals, are clearly correlated with the directly observed rock fabrics. We show that the symmetry directions of the mineral fabric and of microcrack fabric agree. A further result is that the microcrack-induced anisotropy dominates the other causes of anisotropy at confining pressures smaller than a few tens of megapascals, the situation being reversed at higher pressures. The laboratory data are quantitatively compared with sonic log data from the KTB well, showing the influence of pore fluids, effective pressure and crack density reduction on the anisotropy in situ . 相似文献
6.
Effects of stress on the two-dimensional permeability tensor of natural fracture networks 总被引：1，自引：0，他引：1
The effects of stress on the 2-D permeability tensor of natural fracture networks were studied using a numerical method (Universal Distinct Element Code). On the basis of three natural fracture networks sampled around Dounreay, Scotland, numerical modelling was carried out to examine the fluid flow in relation to the variations in burial depth, differential stress and loading direction. It was demonstrated that the permeability of all the networks decreased with depth due to the closure of aperture. The permeability approached the minimum value at some depth below which little further variation occurred. Also, differential stress had a significant effect on both the magnitude and direction of permeability. The permeability generally decreased with increasing major horizontal stress for a fixed minor horizontal stress, but the various networks considered showed different behaviours. A factor, termed the average deviation angle of maximum permeability ( A m ), was defined to describe quantitatively the deviation degree of the direction of the major permeability component from the applied major stress direction. For networks whose behaviour is controlled by set(s) of systematic fractures, A m is significantly greater than zero, whereas those comprised of non-systematic fractures have A m close to zero. In general, fractured rock masses, especially those with one or more sets of systematic fractures, cannot be treated as equivalent porous media. Specification of the geometry of the network is a necessary, but not sufficient, condition for models of fluid flow. Knowledge of the in situ stress, and the deformation it induces, is necessary to predict the behaviour of the rock mass. 相似文献
7.
In the frequency range from millihertz to hundreds of megahertz, many different physical and physico-chemical processes contribute to the electrical polarization of porous water-bearing rocks. This makes the interpretation of their electrical spectra a complicated problem and requires both elaborate theories and model experiments. At high frequencies, the Maxwell–Wagner–Bruggeman–Hanai (MWBH) theory of effective media, which takes into account only bulk properties, shape and partial volume of components, is very appropriate. At low frequencies, surface films, polarization of the electrical double layer (EDL) and clustering of conductive components can produce very strong polarization; corresponding theoretical models are considered in a companion paper ( Chelidze & Gueguen 1999 , hereafter referred to as Paper I). This paper is devoted to the review of experimental data and their comparison with theoretical models.
Experiments on saturated mineral powders and rocks with various surface areas and surface chemistries confirm the existence of significant surface contributions to the electrical spectra of conductivity and polarization of water-bearing rocks and the dominance of this contribution over MWBH values at low frequencies. The effective dielectric constant of porous saturated rocks increases with the surface-to-volume ratio of the system and strongly depends on the surface charge ( ζ potential). At ζ potential, equal to zero, the low-frequency dielectric permittivity (DP) is minimal. The experimental data on relaxation times and the magnitude of the surface polarization of water-bearing porous systems can be satisfactorily explained by theories of film polarization, diffusional polarization generated by deformation of an 'open' electrical double layer (EDL) and percolation. 相似文献
Experiments on saturated mineral powders and rocks with various surface areas and surface chemistries confirm the existence of significant surface contributions to the electrical spectra of conductivity and polarization of water-bearing rocks and the dominance of this contribution over MWBH values at low frequencies. The effective dielectric constant of porous saturated rocks increases with the surface-to-volume ratio of the system and strongly depends on the surface charge ( ζ potential). At ζ potential, equal to zero, the low-frequency dielectric permittivity (DP) is minimal. The experimental data on relaxation times and the magnitude of the surface polarization of water-bearing porous systems can be satisfactorily explained by theories of film polarization, diffusional polarization generated by deformation of an 'open' electrical double layer (EDL) and percolation. 相似文献
8.
基于创新企业的中国城市网络联系特征 总被引：7，自引：0，他引：7
多部门创新企业的跨城布局能够增进城市间的知识流动与创新联系,大量创新企业部门关联构成的城市网络是理解国家创新格局的重要认知基础。本文运用1778家国家级创新企业部门关联数据和“总部—分支机构”方法建立中国城市间有向关系矩阵,借助社会网络分析、GIS技术及空间交互模型方法,对创新企业建构的中国城市网络联系特征进行分析。结果发现：① 基于创新企业的中国城市网络联系覆盖广但极不均质,菱形联系格局在次级网络中逐步显现,京津冀、长三角和珠三角城市群是网络联系的核心枢纽。② 城市间创新企业流具有明显的行政中心指向特征与省级边界效应,直辖市及省会城市对创新企业流具有较强吸引力,北京是网络联系最强核心,上海和深圳次之。③ 城市网络区域异质性突出,东部区域“内联外控”与中、西部区域“内弱外强”的联系格局呈现鲜明对比,东部区域内沿海三大城市群网络的联系结构也存在较大差异。④ 城市的行政等级、经济水平和创新环境等属性指标,以及城市间地理、技术、制度的邻近性关系指标,都对城市吸收和输出创新企业流产生了不同程度的影响,外资并不利于促进中国城际创新企业流和网络的形成。 相似文献
9.
J. P. Cogné 《Geophysical Journal International》1987,91(3):1013-1023
Anisotropic assemblages of multidomain magnetite particles develop an anisotropy of magnetic susceptibility (AMS), which in turn induces deviations of thermo-remanent magnetization (TRM) from the field direction. From the theories of multidomain TRM acquisition, it is shown that the TRM anisotropy tensor has its eigenvalue ratios ( T i ) related to the principal weak-field susceptibility ratios ( P i ) by the order of magnitude T i ≃ P 2 i . This relation has been experimentally verified on two sets of highly anisotropic rock samples. The exponent has been determined to be 1.94 in the samples from a Peruvian gabbro, and 1.81 in those from the granite of Flamanville (NW France). Accounting for experimental difficulties in determining the TRM anisotropy tensors, these exponents are judged to agree well with the expected one. It is therefore stressed that AMS measurements provide a good means of evaluating the magnetic field direction from deviated TRM directions, providing magnetic carriers are mainly multidomain magnetites. 相似文献
10.
Using acoustic emission data obtained from laboratory double torsion tests, we have analysed the fractal nature of a series of 29 granite microfracturing processes in time. The data represent a wide variety of timescales, stress environments (increasing load with a constant displacement rate, relaxation, creep), soaking conditions [air, water, dodecyl trimethyl ammonium bromide (DTAB), polyethelene oxide (PEO) ], and material anisotropy. We find that the time distribution of rock microfracturing displays fractal and multifractal properties. In some cases, it has a single fractal or a multifractal structure. In other cases, it changes from a single fractal structure into a multifractal structure as the system evolves dynamically. We suggest that the heterogeneity of the rock, the distribution of joints or weak planes, the stress level, and the nature of the microfracturing mechanism lead to these multifractal properties. Whatever the fractal structure of the system, a lower fractal dimension is generally produced at near-failure of the rock due to an increased clustering. This result concerning the fractal-dimension decrease is consistent with the conclusion drawn from the spatial distribution of rock microfracturing. Therefore, from the vantage point of observation of the time distribution of rock microfracturing, the decrease of the fractal dimension has a potential use as a rock failure predictor. 相似文献
11.
中国土地覆盖时空变化未来情景分析 总被引：22，自引：6，他引：16
在对HLZ (Holdridge life zone) 分类系统与土地覆盖类型分类系统之间的差异性进行对比分析的基础上,根据土地覆盖类型与HLZ生态系统类型的最大对应概率,构建了基于栅格的土地覆盖边际转换模型。采用基于HadCM3 A1FI、A2a、B2a等三种未来气候变化情景数据模拟获得的中国HLZ生态系统时空变化的系列栅格数据,运行模型后获得相应时段中国未来土地覆盖时空变化情景系列数据。引入土地覆盖类型景观指数及平均中心系列模型和构造平均中心偏移距离及偏移方向的计算模型,对中国未来土地覆盖的景观指数变化及其平均中心的偏移距离、偏移方向及偏移趋势进行综合分析。基于HadCM3 A1FI、A2a、B2a三种情景模拟结果分析表明：在2000~2099年间耕地、草地、湿地、水域、冰川雪被等土地覆盖类型面积逐渐减少,林地、建设用地、荒漠等土地覆盖类型面积逐渐增加,沙漠面积有所减少。其中,林地增加速度最快 (平均每10年增加2.34%),裸露岩石减少速度最快 (平均每10年减少2.38%)。 相似文献
12.
A fine-grained perspective on the robustness of global cargo ship transportation networks 总被引：2，自引：0，他引：2
Peng Peng Shifen Cheng Jinhai Chen Mengdi Liao Lin Wu Xiliang Liu Feng Lu 《地理学报(英文版)》2018,28(7):881-899
The robustness of cargo ship transportation networks is essential to the stability of the world trade system. The current research mainly focuses on the coarse-grained, holistic cargo ship transportation network while ignoring the structural diversity of different sub-networks. In this paper, we evaluate the robustness of the global cargo ship transportation network based on the most recent Automatic Identification System (AIS) data available. First, we subdivide three typical cargo ship transportation networks (i.e., oil tanker, container ship and bulk carrier) from the original cargo ship transportation network. Then, we design statistical indices based on complex network theory and employ four attack strategies, including random attack and three intentional attacks (i.e., degree-based attack, betweenness- based attack and flux-based attack) to evaluate the robustness of the three typical cargo ship transportation networks. Finally, we compare the integrity of the remaining ports of the network when a small proportion of ports lose their function. The results show that 1) compared with the holistic cargo ship transportation network, the fine-grain-based cargo ship transportation networks can fully reflect the pattern and process of global cargo transportation; 2) different cargo ship networks behave heterogeneously in terms of their robustness, with the container network being the weakest and the bulk carrier network being the strongest; and 3) small-scale intentional attacks may have significant influence on the integrity of the container network but a minor impact on the bulk carrier and oil tanker transportation networks. These conclusions can help improve the decision support capabilities in maritime transportation planning and emergency response and facilitate the establishment of a more reliable maritime transportation system. 相似文献
13.
基础设施互联互通是不同区域之间空间网络形成的支撑,对区际生产要素流动、市场融合和资源配置具有重要作用,也是“一带一路”建设的重点内容和前提条件。立足于综合基础设施网络,以“一带一路”沿线国家/地区为分析地域,设计数理模型,评价了中国与沿线国家的基础设施网络连通性,考察其基本特征与空间格局,然后分别从铁路、公路、航运、通讯、能源等各种基础设施方式的视角,分析了不同基础设施网络的互联互通水平,探讨了基础设施连通的类型分异及其主导因素,凝练基础设施连通的空间模式。主要结论如下：① 从海陆属性来看,岛屿型国家与中国设施连通性最高,其次为综合型国家,内陆型国家最低。对国际区域而言,俄蒙和东南亚地区与中国的设施连通性最高,中东欧地区连通性最低。从国家尺度来看,俄罗斯和越南是与中国设施连通水平最高的国家,巴勒斯坦、东帝汶等5个国家与中国尚未形成设施连通性。从连通方式的构成来看,航运网络的连通性最高,其次为航空和光缆。② 空间距离、连通方式和重大交通走廊共同主导了设施连通性的类型分异。③ “一带一路”沿线国家/地区与中国的设施连通形成了四种典型模式,包括海陆融合型外缘连通模式、陆路通道直接连通模式、陆心内生性低水平连通模式、远距离不均衡连通模式。 相似文献
14.
Noga Collins-Kreiner 《The Professional geographer》2013,65(4):589-591
This article explores the conceptual and empirical relationships among connectivity, employment, and specialization in advanced business services (ABS) in major cities in the United States. Correlation and regression analysis produces three chief empirical conclusions: First, the distribution of employment predicts and explains the level of connectivity; second, specialization does not predict connectivity; and, closer examination shows that these results vary by sector, which might relate to the informational characteristics of different types of ABS agglomerations. These conclusions demonstrate the continued relevance of agglomerative dynamics as they influence the networks and hierarchies of the ABS and corporate spatial structures. 相似文献
15.
The first assessment of temperature conditions in Kansas was made by geothermal gradient computations from temperature measurements in shallow boreholes, and these conditions are related to structural patterns, sedimentary cover and underlying basement properties. The area of south-central Kansas was selected for detailed study of geothermal character in relation to the geology. The aim was to quantify the relations and to determine the relationship of different variables of the temperature field. Input parameters included geothermal variables of gradient and temperature, and structure and sediment thickness. Two approaches were used: (1) the numerical computation of theoretical temperature-depth models based on conductive heat transfer, and (2) a map-comparison technique based on algebraic methods. The temperature field information usable for the map comparison is different in response to different measurements (nonequilibrium BHTs and temperatures from logged measurements in equilibrium). Derived from modelled results (plotted isotherms on cross-sections), a close relation between gradients and thermal conductivity of the sediments was confirmed. The most noticeable effect on the geothermal field, as noted quantitatively from the map-comparison study, is the relation of thickness of outcropping Permo-Pennsylvanian units because of their different thermal conductivity. The eastward increase of mean gradients is inversely related to the total sediment thickness, but this is mostly recognizable using the shallow temperature gradients. This dissimilarity gives additional evidence for a close link between gradients and thermal conductivity of the sediments in which the temperature measurements were made. The effect caused by the structure in deeper (older) units is not important and seems not to be significant, nor is the influence of the basement rock composition as indicated by the temperature modelling. 相似文献
16.
基于2003—2018年长三角地区跨国、跨区以及区内企业异地投资数据,融合社会网络分析、面板向量自回归模型和地理加权回归模型等方法,探究长三角地区多尺度城市网络空间演化及其动态互馈效应。结果表明：① 全球、全国和区域尺度城市网络分别处于初步发展、稳步发展和完善发展阶段,各尺度网络均呈现出区域化倾向,以沪宁合杭甬发展廊道为支撑的网络空间结构正在形成。② 城市的全球与全国功能联系之间存在相互促进的关系;城市的区域功能联系提升能够促使其融入全球和全国尺度城市网络,反之,城市的全球与全国功能联系提升却未能促进其进一步融入长三角内部城市网络,融入全球尺度城市网络甚至对城市的区域功能联系产生显著的抑制作用。此外,多尺度城市网络互馈效应具有明显的空间异质性,并与区域经济发展格局相耦合。 相似文献
17.
A post-tectonic Caledonian granite in southern Ny Friesland has been fully mapped and the following new names are proposed: the Chydeniusbreen granitoid suite, consisting of the Raudberget granitoid body in the north; the Newtontoppen granitoid body in the middle; and the Ekkoknausane granitoid body in the south
The contact relationships, internal structures and distribution of various rock types infer an asymmetric lopolith or a harpolith-like body, a large sickle-shaped intrusion stretched in the direction of general tectonic transport, for the Newtontoppen granitoid body.
Seven rock types are described in the Newtontoppen granitoid and four emplacement stages are recognised. The major rock types seem to have an alkali-calcic to alkalic bulk rock chemistry and show a transition between I- and S-type granite derived from anatectic melting of various protoliths under relatively high temperature conditions. Possible later K2 0 introduction modified the earlier formed rock types.
A Rb-Sr whole rock age of 432 ± 10 Ma has been obtained by a seven point isochron with MSDW = 2.59 and an initial Sr isotope ratio = 0.715. This age is approximately 30 Ma older than the previously obtained K-Ar whole rock and Rb-Sr biotite ages, ca. 400 Ma, which represents the period of cooling. The high initial Sr isotope ratio supports the interpretation of an anatectic origin. 相似文献
The contact relationships, internal structures and distribution of various rock types infer an asymmetric lopolith or a harpolith-like body, a large sickle-shaped intrusion stretched in the direction of general tectonic transport, for the Newtontoppen granitoid body.
Seven rock types are described in the Newtontoppen granitoid and four emplacement stages are recognised. The major rock types seem to have an alkali-calcic to alkalic bulk rock chemistry and show a transition between I- and S-type granite derived from anatectic melting of various protoliths under relatively high temperature conditions. Possible later K
A Rb-Sr whole rock age of 432 ± 10 Ma has been obtained by a seven point isochron with MSDW = 2.59 and an initial Sr isotope ratio = 0.715. This age is approximately 30 Ma older than the previously obtained K-Ar whole rock and Rb-Sr biotite ages, ca. 400 Ma, which represents the period of cooling. The high initial Sr isotope ratio supports the interpretation of an anatectic origin. 相似文献
18.
To quantify the seismic properties of lower crustal rocks and to better constrain the origin of the lower crustal seismic reflectivity, we determined the complete 3-D seismic properties of a lower crustal section. Eight representative samples of the main lithologic and structural units outcropping in the Val Sesia (Ivrea zone) were studied in detail. The seismic velocities were calculated using the single crystal stiffness coefficients and the lattice preferred orientation (LPO) of each mineral in all samples. The 21 stiffness coefficients characterizing the elastic behaviour of each rock are determined. Mafic and ultramafic rocks such as pyroxenite and pyroxene-bearing gabbros display complex shear wave properties. These rocks are weakly birefringent (maximum 0.1 kms−1 ) and it is difficult to find consistent relationships between the seismic properties and the rock structure. On the other hand, seismic properties of deformed felsic rocks are essentially controlled by mica. They display strong S -wave birefringence (0.3 km s−1 ) and relatively high V p anisotropy (7.6 per cent). Amphibole also strongly influences the rock birefringence patterns. For both kind of rocks, the foliation is highly birefringent and the fast polarized shear wave is systematically oriented parallel to the foliation. We show that the number of mineral phases in the rock strongly controls the anisotropy. The seismic anisotropy has a complex role in the P -wave reflectivity. Compared to the isotropic case, anisotropy enhances the reflection coefficient for about 60 per cent of the possible lithological interfaces. For 40 per cent of the interfaces, the reflection coefficient is much lower when one considers the medium as anisotropic. 相似文献
19.
Convective and conductive heat transfer in sedimentary basins 总被引：1，自引：0，他引：1
In the Earth's crust the temperature is largely controlled by heat conduction. However, under some circumstances, the thermal state is disturbed by advection of heat associated with groundwater flow. The corresponding thermal disturbance depends on the water flow velocity (modulus and direction) and therefore thermal data may be used to constrain the pattern of natural fluid flow. In this paper, some models of thermal disturbance induced by convective heat transfer are presented. They are based on the assumption that the water flow is concentrated in thin permeable structures such as aquifer or fault zones. The steady-state and transient thermal effects associated with such scenarios are computed using a somewhat idealized model which depends on a small number of parameters: flow rate, time, aquifer geometry and thermal parameters of surrounding rocks. In order to extract the conductive and convective components of heat transfer from temperature data and to estimate the corresponding fluid flow rate, it is first necessary to estimate the thermal conductivity field. The problem of the estimation of thermal conductivity in clay-rich rocks, based on laboratory and in-situ measurements, is emphasized. Then a method is proposed for the inversion of temperature data in terms of fluid flow. Vertical and lateral variations of thermal conductivity are taken into account and the fluid flow is assumed to be concentrated on a specified surface (2-D quasi-horizontal pattern). Thermal effects of the flow are simulated by a distribution of surface heat production which can be calculated and then inverted in terms of horizontal fluid flow pattern. 相似文献
20.
The formation processes of the late Neogene sedimentary basins in Northern Hokkaido have been investigated on the basis of rock magnetism, structural geology and numerical modelling. Untilted site‐mean directions of remanent magnetization of the Wakkanai Formation, obtained from oriented core samples in Horonobe, suggest remarkable counterclockwise block rotation (ca. 70°) since the late Neogene. Uniform microscopic fabric of the siliceous sediments was inferred from the alignment of the principal axes of the anisotropy of magnetic susceptibility (AMS). After correction for tectonic rotation, the maximum axis of AMS, which reflects the sedimentary fabric of the dominant paramagnetic minerals, is in an E‐W direction, which is concordant with the influx direction of diatomaceous particles into the N‐S elongate sedimentary basins. The difference in the bulk initial magnetic susceptibility of the siliceous sediments of the Wakkanai Formation between the depocenter of the basin and its peripheral part implies that terrigenous non‐magnetic fraction has been sorted out during transportation of the detrital grains as gravity flows. As for the development mechanism of the N‐S elongate late Neogene basins in Northern Hokkaido, their depocenter arrangement and subsidence pattern indicates dextral motions upon a longitudinal fault zone along the Eurasian convergent margin. Dislocation modelling was adopted to explain vertical displacement and rotational motion around the study area and successfully restored the deformation pattern based on the assumption of dextral slip at a left‐stepping part of a strand of the transcurrent fault. 相似文献