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1.
The position of the dip equator (de) is worked out in the Indian region based on fairly close geomagnetic measurements made during a survey in the year 1981. Thede is located about 24 km south of its 1971 position along the 77·5°E meridian. Also, thede positions for the epochs 1971 and 1981 show closeness on the east coast of India when compared to its west coast positions. Thede positions inferred from the repeat observations since 1909 are used for estimating the pattern of migration and the results are discussed. 相似文献
2.
Kshudiram Saha 《Journal of Earth System Science》1993,102(1):241-247
Using the theory of plate tectonics and a concept of climate analogs, the paper speculates that a monsoon type of climate
with warm and wet summer and cold and dry winter might have first appeared over the northern part of India when during its
northward drift across the Tethys Ocean (now the Indian Ocean) it was located over the subtropical belt of the southern hemisphere
some 60 million years before present (BP). The monsoon climate gradually evolved and extended to other parts of India as the
Indian plate after crossing the equator about SO million years BP moved further northward and collided against the north Asian
plate giving rise to the Himalayas along the northern boundary of India some 40 million years BP. Recent studies suggest that
despite short and long period fluctuations, no major secular change or trend has taken place in the monsoon climate of India
since then. 相似文献
3.
This paper describes the morphology of the equatorial electrojet (EEJ) along 45°W longitude in east Brazil, where the ground
magnetic (dip) equator is associated with the largest declination in the world. Daily range of the horizontal field (ΔH), as expected, was largest at the station in the chain closest to the dip equator, Sao Luiz (inclination −0.25°S). ΔZ was largest positive at Eusebio (inclination 9.34°S) and largest negative at Belem (inclination 7.06°N); both near the fringe
of EEJ belt. ΔZ at Sao Luiz during the daytime was unexpectedly large negative in-spite of a small dip and also located south of the dip
equator where ΔZ should be positive. Center of EEJ was found to be shifted southward of the dip equator by about 1° in latitude. During southern
summer, ΔY started decreasing from 00 h and reached a minimum value in the afternoon, an abnormal feature not discussed for any station
so far. The mid-day value of the direction of ΔH vector was 22°–24°W compared to the declination of 19°–21°W in the region. 相似文献
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6.
Mahfoud Benaissa M. C. Berguig V. Doumbia S. Bouraoui 《Arabian Journal of Geosciences》2017,10(15):329
The equatorial electrojet (EEJ) is an intense daytime ionospheric current that circulates eastward along the geomagnetic dip equator. In this work, the EEJ current intensity was studied from ground-based magnetic data and CHAllenging Minisatellite Playoad (CHAMP) satellite observations. The ground-based magnetic data were recorded along a meridian chain of three stations across the dip equator in West Africa. These stations were operated by the Institut de Physique du Globe de Paris (IPGP). For the CHAMP satellite data, vector magnetometer records during geomagnetically quiet periods with Kp?≤?2 were used. To estimate the EEJ current intensity, we have first isolated its magnetic effect from CHAMP satellite observations for 10 years (from July 2000 to September 2010). The results were used to analyze the EEJ seasonal variability and the local time and longitude dependence. In addition, a comparison between ground-based and satellite observations of the EEJ current intensity was made. A good correlation was found between satellite and ground-based EEJ current intensity, with an average correlation coefficient of r 2 ~0.93. This performed correlation show that the technique used in this study can be extended to all ground magnetic stations for modeling the EEJ phenomena. 相似文献
7.
影响波动方程叠前深度偏移成像精度的主要因素除了要求勘探区覆盖次数均匀、单炮记录信噪比高外,还必须建立准确的偏移速度场及选择合适的偏移孔径,其中速度深度模型的建立原则取决于偏移后共反射点道集同相轴是否呈水平形态,而偏移孔径的选择依据则是目的层倾角的大小。在地层倾角变化剧烈的吉新煤矿区,深度域层速度场采用三次速度迭代求得,并确定偏移孔径为600m×600m。应用表明：叠前深度偏移比叠后时间偏移处理在复杂构造区成像准确、断点空间位置清晰,且在解决复杂地质构造成像问题的同时还能够提高资料的信噪比和分辨率,是解决复杂构造成像的有效工具。 相似文献
8.
Anumeha Shukla Rakesh Chandra Mehrotra 《Journal of the Geological Society of India》2016,87(5):520-524
Thick lignite deposits on the western margin of India were preserved on account of thick vegetation which got buried underneath due to tectonic activities that occurred in northwestern part of India during the early Palaeogene. Study of the fossil flora preserved in these beds is important to deduce the palaeoclimate of the region. Therefore, a field work was undertaken to collect plant fossils from the Tarkeshwar lignite mine, Surat district, Gujarat (western India) which is still unexplored as far as the plant mega-remains are concerned. A fossil wood is systematically described from the Cambay Shale Formation of the mine considered to be of early Eocene in age. It shows close affinities with Holigarna (Anacardiaceae), particularly with H. beddomei and H. grahamii. This genus is evergreen in nature and grows in the Indo-Malayan region, while both the modern analogues of the fossil are endemic to semi-evergreen to evergreen forests ofWestern Ghats, south India, located at the equator. This not only confirms the palaeolatitudinal position of the Indian subcontinent at the equator during the early Palaeogene, but also indicates the presence of equatorial rain forest in the Indian subcontinent during the period. Based on the timetree, Sapindales started to diverge in the early Palaeocene (62–57 Ma) as its oldest fossil is from the K-Pg boundary. Discovery of the present anacardiaceous fossil (belonging to Sapindales) from the early Eocene strengthens the above phylogenetic view. 相似文献
9.
Faraday rotation measurements made at a chain of stations and group delay measurements made at Ootacamund from ATS-6 are examined for the partial solar eclipse event of 29 April 1976. There is no evidence of eclipse-induced gravity waves in these measurements extending from Ootacamund near dip equator to Patiala (dip 45° N). Eclipse-induced fluctuations were however reported at Trivandrum, about 300 km south of Ootacamund. 相似文献
10.
尼勒克井田的浅表层地震地质条件差，深部地质构造复杂，地层倾角大。通过建立地质构造模型，反演出高倾角地层的地震记录，针对高倾角地层地震反射波的特点，采用小道距观测，在资料处理方法上着重注意原始资料分析、静校正处理、反褶积测试、叠前偏移技术等环节。该区勘探结果表明：在高倾角地层从事地震勘探，首先要根据地震地质条件作好构造模型及反演记录，着重做好变观措施，其次选取合理的处理模块，做好叠前偏移技术，兼顾干扰波去除，即可获得满意的勘探效果。 相似文献
11.
Ebun Oni 《Tectonophysics》1977,38(3-4)
Some deductions made from the magnetic anomaly profile of a body that had retained its strong negative permanent magnetization in the vertical field component, near the dip equator, has been utilized to supply information on a possible north—south shift of the western sector of the African plate. This constitutes a new approach to the tectonic physics of the African plate. 相似文献
12.
Electrical conductivity structure of the Earth’s deep interior has been successfully mapped out down to approximately 1500 km around the geomagnetic dip equatorial regions of Africa using solar quiet-day ionospheric currents. Spherical harmonic analysis (SHA) was employed in separating the internal and external field contributions to the solar quiet variations. Transfer function was used for each of the external and internal pairs to compute the conductivity-depth profile for the region. Calculated average electrical conductivity values were evidently higher than obtained in other parts of the world farther away from the geomagnetic equator. Sq current vortex foci are observed very close to the geomagnetic equator. Depth of penetration was greatly enhanced. Stations on latitudes less than 1° from the geomagnetic equator show higher electrical conductivity when compared with that situated more than 4° away from it at various corresponding depths. Evidence of discontinuities in the earth layers were also noted at some depths. Highly conductive layers were delineated around 400 km depth and beyond 1200 km. 相似文献
13.
偏移速度分析和偏移成像是地震资料处理的两个重要组成部分.目前时间偏移技术比较成熟,而深度偏移技术也在逐步完善,时间域偏移成像主要推崇叠前时间偏移法.采用沿层叠加速度分析技术可获得层面上准确的叠加速度,并通过倾角校正、叠前时间偏移和CRP反偏移速度分析逐步优化速度,得到一个符合地质规律、准确的均方根速度场;通过深度偏移方法的研究,总结了建立精确偏移速度场的方法,并提出了一种地震资料处理的思路,即基于射线追踪的Kirchhoff偏移和基于波场延拓的波动方程偏移的结合,使偏移速度分析和偏移成像在应用效果和效率上得到了很大的提高. 相似文献
14.
地震照明分析能够定量分析影响逆时偏移成像质量的因素。文章基于Poynting矢量方法进行地震定向照明分析及成像补偿方法研究,利用Poynting矢量进行波场传播角度分解,通过计算不同入射及散射波方向的部分照明建立局部照明矩阵。该矩阵包含了照明分析中波与地质结构相互作用所涉及的所有角度信息,可以方便地分析目标附近所有可能的入射波和散射波对局部照明的贡献。根据局部照明矩阵可以获得对地下结构的照明描述、采集倾角响应,并依此进行成像补偿计算。以SEG/EAGE模型作为数值计算实例,进行基于Poynting矢量的照明分析及成像补偿,有效地提高了成像质量。该方法为角度域逆时偏移成像校正及分辨率分析等提供了高效的处理手段。 相似文献
15.
文章选用四氯乙烯（PCE）为代表性重非水相液体（DNAPL）,采用透射光法监测PCE在单裂隙介质中的运移过程和形态分布,探究流速及裂隙面倾斜度对PCE运移分布行为的影响。结果表明,单裂隙介质中PCE呈团块状脱离注样针,并在运移过程中呈近椭圆状。地下水流速越大,初始面积Fs越大,近椭圆的PCE离心率e越小;裂隙面倾斜度越大,初始面积Fs越小,近椭圆的PCE离心率e越小。不同流速或倾斜度条件下,入渗稳定后的PCE团块面积与离心率均明显下降。地下水流速及裂隙面倾斜度的增大对于PCE纵向运移具有促进作用,使PCE污染物前端锋面运移速率增大,在相同时间内更快运移到裂隙底部。PCE入渗停止后,流速增大促使污染源区PCE饱和度降低,使饱和度峰值随水流速度增大而减小;倾斜度增大抑制污染源区PCE饱和度降低,使饱和度峰值随倾斜度增大而增大。 相似文献
16.
G K Rangarajan 《Journal of Earth System Science》1981,90(1):55-62
Mean diurnal variation ofH at low and equatorial latitudes is computed for days in the vicinity of passage of ‘quiet’ solar wind. It is shown that the prepassage magnitude of the diurnal variation is appreciably larger when compared to post-passage intervals at low latitudes but the difference vanishes in the electrojet region. It is suggested that the Sq current system moves towards dip equator immediately following quiet wind conditions relative to earlier periods. It is also shown that during conditions of stable solar wind, the solar wind proton density is inversely related to the electrojet strength, while at low latitudes outside the jet influence, there is no clear association. 相似文献
17.
上拱力构造背景下形成的正断裂及断裂极限应力状态研究在构造解释和油气运移成藏中具有重要的意义。在抛物线型莫尔包络线理论的基础上,通过合理的假设和数学推导以及理论模拟,进一步探讨上拱力构造背景影响下形成的正断裂剖面形态和断裂的极限应力状态,并定量给出函数表达式。研究结果表明,断裂在均质岩体中由浅到深,倾角从竖直开始由大变小,呈铲状断裂,而变化的速率只与地层物性有关,泥岩比砂岩变化快。断裂分布的深度与上拱力的大小成一次线性关系,上拱力越大,断裂分布越浅。砂泥岩互层地层中发育有典型的坡坪式正断裂。研究结果不仅与普遍认识相一致,而且可以进一步在实际应用中预测断裂的存在,定量解释断裂形态,求取上拱力和断裂极限应力状态。 相似文献
18.
受技术条件限制,以往采区地震资料多采用叠后时间偏移处理方法。实践证明该方法在地层倾角大、断层发育等地质条件复杂地区,很难准确成像。采用Kirchhoff叠前时间偏移的方法,合理配置参数,可以有效解决速度横向变化不大但倾角变化剧烈条件下三维地震成像精度低的问题。通过对淮北某矿区三维地震老资料应用叠前时间偏移处理结果表明：经过叠前时问偏移处理得到的数据体,其反射波特征明晰,经解释修正原断层7条、否定原断层2条、新发现断层4条,其中修正后的DF3断层已得到矿方的揭露验证,地震解释的断层性质、空间位置与实际揭露情况吻合良好。 相似文献
19.
The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle 总被引：1，自引：0，他引：1
A geodynamic model exists, the westward lithospheric drift model, in which the variety of overriding plate deformation, trench migration and slab dip angles is explained by the polarity of subduction zones. The model predicts overriding plate extension, a fixed trench and a steep slab dip for westward-dipping subduction zones (e.g. Mariana) and predicts overriding plate shortening, oceanward trench retreat and a gentle slab dip for east to northeastward-dipping subduction zones (e.g. Chile). This paper investigates these predictions quantitatively with a global subduction zone analysis. The results show overriding plate extension for all dip directions (azimuth α = − 180° to 180°) and overriding plate shortening for dip directions with α = − 90° to 110°. The wide scatter in data negate any obvious trend and only local mean values in overriding plate deformation rate indicate that overriding plate extension is somewhat more prevalent for west-dipping slabs. West-dipping subduction zones are never fixed, irrespective of the choice of reference frame, while east to northeast-dipping subduction zones are both retreating and advancing in five out of seven global reference frames. In addition, westward-dipping subduction zones have a range in trench-migration velocities that is twice the magnitude of that for east to northeastward-dipping slabs. Finally, there is no recognizable correlation between slab dip direction and slab dip angle. East to northeast-dipping slabs (α = 30° to 120°) have shallow (0–125 km) slab dip angles in the range 10–60° and deep (125–670 km) slab dip angles in the range 40–82°, while west-dipping slabs (α = − 60° to − 120°) have shallow slab dip angles in the range 19–50° and deep slab dip angles in the range 25–86°. Local mean deep slab dip angles are nearly identical for east and west-dipping slabs, while local mean shallow slab dip angles are lower by only 4.7–8.1° for east to northeast-dipping slabs. It is thus concluded that overall, there is no observational basis to support the three predictions made by the westward drift model, and for some sub-predictions the observational basis is very weak at most. Alternative models, which incorporate and underline the importance of slab buoyancy-driven trench migration, slab width and overriding plate motion, are better candidates to explain the complexity of subduction zones, including the variety in trench-migration velocities, overriding plate deformation and slab dip angles. 相似文献
20.
基于双程波动方程的逆时偏移（RTM）具有原理简单、无倾角限制、可以适用于速度任意变化的模型,并具有对各类波正确成像等优点,是当今最好的偏移方法之一.本文阐述了逆时偏移存在的缺陷并分析了低频噪声的产生机制,重点探讨了使用波场分离的逆时偏移去噪方法,并通过模型的试算证明了该方法的有效性. 相似文献