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961.
962.
Xiaorong Luo 《Earth and Planetary Science Letters》2002,201(2):431-446
Natural hydrofracturing caused by overpressure plays an important role in geopressure evolution and hydrocarbon migration in petroliferous basins. Its mechanism is quite well understood in the case of artificial hydraulic fracturing triggered by high-pressure fluid injection in a well. This is not so for natural hydraulic fracturing which is assumed to initiate as micro-cracks with large influence on the permeability of the medium. The mechanism of natural hydraulic cracking, triggered by increasing pore pressure during geological periods, is studied using a fracturing model coupled to the physical processes occurring during basin evolution. In this model, the hydraulic cracking threshold is assumed to lie between the classical failure limit and the beginning of dilatancy. Fluid pressure evolution is calculated iteratively in order to allow dynamic adjustment of permeability so that the fracturing limit is always preserved. The increase of permeability is interpreted on the basis of equivalent fractures. It is found that fracturing is very efficient to keep a stress level at the rock’s hydraulic cracking limit: a fracture permeability one order of magnitude larger than the intrinsic permeability of the rock would be enough. Observations reported from actual basins and model results strongly suggest that natural hydraulic cracking occurs continuously to keep the pressure at the fracturing limit under relaxed stress conditions. 相似文献
963.
Gravity and magnetic signatures of volcanic plugs related to Deccan volcanism in Saurashtra, India and their physical and geochemical properties 总被引:1,自引:0,他引:1
D.V. ChandrasekharD.C. Mishra G.V.S. Poornachandra RaoJ. Mallikharjuna Rao 《Earth and Planetary Science Letters》2002,201(2):277-292
The Bouguer anomaly and the total intensity magnetic maps of Saurashtra have delineated six circular gravity highs and magnetic anomalies of 40-60 mGal (10−5m/s2) and 800-1000 nT, respectively. Three of them in western Saurashtra coincide with known volcanic plugs associated with Deccan Volcanic Province (DVP), while the other three in SE Saurashtra coincide with rather concealed plugs exposed partially. The DVP represents different phases of eruption during 65.5±2.5 Ma from the Reunion plume. The geochemical data of the exposed rock samples from these plugs exhibit a wide variation in source composition, which varies from ultramafic/mafic to felsic composition of volcanic plugs in western Saurashtra and an alkaline composition for those in SE Saurashtra. Detailed studies of granophyres and alkaline rocks from these volcanic plugs reveal a calc-alkaline differentiation trend and a continental tectonic setting of emplacement. The alkaline plugs of SE Saurashtra are associated with NE-SW oriented structural trends, related to the Gulf of Cambay and the Cambay rift basin along the track of the Reunion plume. This indicates a deeper source for these plugs compared to those in the western part and may represent the primary source magma. The Junagadh plug with well differentiated ring complexes in western Saurashtra shows well defined centers of magnetic anomaly while the magnetic anomalies due to other plugs are diffused though of the same amplitude. This implies that other plugs are also associated with mafic/ultramafic components, which may not be differentiated and may be present at subsurface levels. Paleomagnetic measurements on surface rock samples from DVP in Saurashtra suggest a susceptibility of 5.5×10−2 SI units with an average Koenigsberger ratio (Qn) of almost one and average direction of remanent magnetization of D=147.4° and I=+56.1°. The virtual geomagnetic pole (VGP) position computed from the mean direction of magnetization for the volcanic plugs and Deccan basalt of Saurashtra is 30°N and 74°W, which is close to the VGP position corresponding to the early phases of Deccan eruption. Modeling of gravity and magnetic anomalies along two representative profiles across Junagadh and Barda volcanic plugs suggest a bulk density of 2900 and 2880 kg/m3, respectively and susceptibility of 3.14×10−2 SI units with a Qn ratio of 0.56 which are within the range of their values obtained from laboratory measurements on exposed rock samples. The same order of gravity and magnetic anomalies observed over the volcanic plugs of Saurashtra indicates almost similar bulk physical properties for them. The inferred directions of magnetization from magnetic anomalies, however, are D=337° and 340° and I=−38° and −50° which represent the bulk direction of magnetization and also indicate a reversal of the magnetic field during the eruption of these plugs. Some of these plugs are associated with seismic activities of magnitude ≤4 at their contacts. Based on this analysis, other circular/semi-circular gravity highs of NW India can be qualitatively attributed to similar subsurface volcanic plugs. 相似文献
964.
Positive tectonic inversion is related to the transmission of compressional stresses along a décollement into the foreland of an orogenic zone. This stress and strain concentration in regions remote from the main orogenic front is commonly related to the presence of pre-existing rheological heterogeneities such as normal syn-depositional faults. During inversion, these pre-existing normal faults are reactivated as reverse faults. Tectonic inversion in the Rhenohercynian fold-and-thrust belt during the Variscan Orogeny shows that inversion is likely synchronous with the onset of collision in the hinterland. Here, we present the results of a simplified thermo-mechanical model (STM) which allows one to study strain partitioning between two orogenic zones. We show that, if the two orogenic zones have the same mechanical properties, the viscosity of the décollement, which links them, controls the initial strain partitioning. During subsequent finite shortening, erosional processes determine the partitioning of strain rate. The presence of a weak structure in the inverted zone and of a low-viscosity décollement leads to initial strain concentration in the inverted track rather than in the collision zone and a progressive decrease in strain partitioning between the two orogenic zones. The STM results are in good agreement with results of a 2D finite-element model. We conclude that, in the western part of the Rhenohercynian Massif, simultaneous uplift and deformation within the Mid-German Crystalline Rise (the main collision zone) and the Ardenne Anticlinorium (the inverted zone) lead to interpreting this orogenic event as a case of vice tectonic rather than the propagation of a ‘wave of folding’ towards the Variscan front, as suggested by previous authors. 相似文献
965.
地球物理技术在我国考古和文物保护工作中的应用 总被引:3,自引:6,他引:3
20世纪80年代以来,我国考古及文物保护工作者和地球物理工作者越来越认识到地球物理技术在考古和方物保护方面可以发挥作用,在古幕探查、大型古建筑地下遗存现状、古遗迹断代等方面,地球物理技术都找到了发挥作用的机会,本文通过地球物理技术在云冈石窟、龙门石窟、克孜尔石窟、北京故宫紫禁城、嵩岳寺塔、古泗州城遗址、风阳明中都等的物理探查实例,以及查找古幕、古遗迹断代等方面的工作,介绍了我国在考古和文物保护领域应用地球物理技术的进展,并指出了物探在用于考古和文保时的特点和展望。 相似文献
966.
967.
DAS24-3B是中国科学院地质与地球物理研究所研制的宽频带地震数据采集系统。采集控制模块是该系统的重要组成部分。本文阐述了控制模块的工作原理,介绍了DAS24-3B系统的基本组成和采集器工作过程,并给出该系统如何与笔记本端应用程序界面通讯和联络的操作建议,使该系统能够在工作中发挥更大的作用。 相似文献
968.
969.
东营市森林火险天气等级预报系统 总被引:2,自引:0,他引:2
利用9210传输的气象资料,选用国家气象中心T106和HLAFS数值预报产品中的要素作为火险天气因子,根据森林火险原因,建立了东营市森林火险天气等级预报系统。 相似文献
970.
介绍了利用卫星云图资料估算黄河中游面雨量的基本方法:将GMS卫星1h间隔的可风和红外云图作为判别的两个特性进行分类,确定红外光线资料的所有最小值点作为对流核;多参照Negri-Adler的方法,应用斜率参数消除卷云;应用-维云模式确定红外线图上对流核的降水率,层状云降水通过一个温度阈值给出。另外,通过2001年7月26日至28日黄河流域出现的一次较强降雨过程进行应用分析,得出结论--利用卫星云图估算黄河中游地区平均雨量的方法具有很好的实用价值。 相似文献