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A series of precisely repeated magnetic surveys has been carried out over a five year period, during the filling of Lake Gordon, Tasmania, following construction of a dam. After subtraction of the secular variation gradient over the region, a mean decrease of 1.6 nT in total field intensity is found over the survey area, which exceeds 600 km2, corresponding to the expected form of a tectonomagnetic anomaly due to ground loading. During the survey period there were several local magnetic events, coinciding with more rapid, local changes in benchmark levels, that may be attributed to aseismic movements on faults in the area. 相似文献
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This paper presents relative secular variations of the total intensity of the geomagnetic field against a background of results of magnetic anomaly interpretation along seismic profile P4. Profile P4 crosses a Variscan folding zone in the Paleozoic Platform (PLZ), the Trans-European Suture Zone (TESZ), and the Polish part of the East European Craton (EEC). Secular geomagnetic field variations
measured in 1966–2000 along a line adjacent to seismic profile P4 were analysed. The study of secular variations, reduced to the base recordings at the Belsk Magnetic Observatory, showed that the growth of geomagnetic field at the East European Craton was slower than in the Trans-European Suture Zone and the Paleozoic Platform.A 2D crustal magnetic model was interpreted as a result of magnetic modelling, in which seismic, geological and geothermal data were also used. The modelling showed that there were significant differences in the magnetic model for geotectonic units, which had been earlier determined based on deep seismic survey data. It should be noted that a fundamental change of trend of the relative secular variations was observed at the slope of the Precambrian Platform. After analysing the geomagnetic field observed along profile P4, the hypothesis that the contact between Phanerozoic and Precambrian Europe lies in Poland's territory can be proven. 相似文献
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B R Arora V H Badshah B P Singh M G Arur P S Bains Jeevan Lal 《Journal of Earth System Science》1983,92(1):15-30
The magnetic measurements of declination (D), horizontal (H) and vertical (Z) components of earth’s magnetic field, collected from ground surveys between 1962 and 1966, are used to develop an analytical model of geomagnetic field variations over Indian region for the epoch 1965. In order to reflect spatial features with wavelengths of approximately 1000 km, sixth degree polynomial as a function of differential latitude and longitude is calculated by the method of least squares. The root mean square fit of the model to the input data is better than that accounted by the International Geomagnetic Reference Field for 1965.0. Isomagnetic charts drawn forD, H, Z and total force (F) reflect more details than that shown on world magnetic charts. Further, the values of the field at common repeat stations recorded between 1962 and 1974, after eliminating the field values for the epoch 1965.0, are used to get the secular variation as well as its spatial dependence again by means of polynomial which now includes coefficients which are functions of time and of geographical locations. The accuracy of coefficients is tested against the behaviour of secular variation at permanent magnetic observatories. The merits and limitations of the model are discussed. 相似文献
5.
Piston cores 7 m and 6.5 m long were collected from Lakes Zug and Zurich respectively. Radiocarbon age determinations, pollen assemblage zones and varve counts indicate dates of 5000–6000 years B.P. (Zug), and 12,000–13,000 years B.P. (Zurich) for the base of the cores. Declination of the magnetic remanence varies through 70° and inclination varies through 30°. Although the correlation with the geomagnetic secular variation curve covering the last 15,000 years as determined from Lake Windermere, England (Creer et al., 1972) is not precise, the results suggest that Lake Zug and Lake Zurich sediments have been recording the broad outline of past secular variations of the earth's magnetic field. Since intensity of magnetization and susceptibility correlate markedly with lithology, a detailed sediment stratigraphy is presented. The amount and texture of the detrital input appears to be a controlling factor for the natural magnetic remanence. Intensity varies from 90 μG in zones of organic, sulphide pigmentation and those with ultra-fine laminations to 0.8 μG in impure lacustrine chalk. Susceptibility ranges from 9 μG/Oe in laminated, fine-grained glacially derived muds to 0.5 μG/Oe in impure lacustrine chalk. Intensity of magnetization also varies systematically within individual turbidites with lowest values in the coarse-grained, basal fractions. Slumped beds were identified on the basis of erratic anomalies in magnetic declination and inclination measurements. 相似文献
6.
Geomagnetic effects related to the stresses induced by the water load of the Chiotas reservoir (NW Italy) were studied, with measurements of the geomagnetic field at different stages of filling. The highest effect, mean 7 nT, was recorded at three-quarters full; subsequently, as the volume of water increased, the anomalous variations fell to about 2 nT. 相似文献
7.
Archaeomagnetic dates derived from geomagnetic field direction records in baked materials are proposed for a mediaeval brick kiln (from inclination I and declination D) and for bricks from a brick wall (from I only) in northern Belgium. They are used to verify whether a brick chronology based on the format of bricks is feasible in Flanders. The brick kiln yielded a highly reliable average magnetization direction corresponding to an archaeomagnetic date around A.D. 1650, using the British and French geomagnetic field secular variation curves as a reference, at least half a century younger than expected from historical data. The fidelity of the geomagnetic records was controlled by measuring the magnetic anisotropy of the bricks. Anisotropy of magnetic susceptibility (AMS) measurements demonstrate that the bricks have a shape related magnetic fabric, which is induced during the molding process. A test to control whether AMS can substitute for the anisotropy of thermo‐remanent magnetization (ATRM) failed because of induced changes during laboratory heating. © 2003 Wiley Periodicals, Inc. 相似文献
8.
基于我国大陆最新观测所得的1 302个地磁测点和32个地磁台站磁偏角D、磁倾角I、总强度F的1 334组准确数据,并结合地壳磁异常能谱变化特征,对增强地磁模型(EMM2010)在我国大陆的精度及其适用性进行了定量分析。结果表明：EMM2010模型(D、I、F)在我国大陆的总体精度分别为10.45′、8.08′、112.85 nT ;东北、华北与新疆地区模型的精度为13.07′、8.90′、130.89 nT ;华南、青藏高原及其东缘地区模型的精度为7.07′、6.65′、81.84 nT;其精度是受模型有限的截断阶数、各区域的磁异常状况和磁测数据的误差等因素共同影响的。EMM2010模型的精度在我国大陆表现出显著的地域分布特征,与磁异常的分布形态及其复杂程度、梯度密切相关,异常越突出,形态越复杂,模型的精度越低。与世界地磁模型(WMM2010)、第11代国际参考地磁场(IGRF11)相比,EMM2010模型在我国大陆的总体精度平均提高了50%,主要原因是模型不仅包含了地球主磁场,同时还包含了地壳磁场。EMM2010模型应用于我国大陆的实例及精度分析表明,模型具有一定的适用性,但有其局限性,不能准确反映出我国大陆的地磁场信息,鉴于模型的精度,建议在EMM2010模型基础上,结合我国最新的各部门的高精度磁测数据,构建我国高精度的地磁场模型。 相似文献
9.
Tsvetkov Yu. P. Kuznetsov V. D. Golovkov V. P. Brekhov O. M. Pelle V. A. Krapivnyi A. V. Nikolaev N. S. 《Doklady Earth Sciences》2011,436(1):117-121
The solution to the problem of extraction of the anomaly Earth’s magnetic field (EMF) from stratospheric balloon magnetic
surveys with the help of global analytical models of the normal EMF is proposed. In the problem solution, errors for the analytical
models of the normal EMF and its secular variation at a set moment of time are assessed; the found error is introduced as
a correction to the extracted anomaly EMF. The error of the model is determined in the places where significant magnetic anomalies
are absent. In this case, the error of the model corresponds to deviations of the normal EMF components, synthesized by coefficients
of analytical models, and to deviations of the EMF secular variations from the measured values at quite a low value of the
variable EMF or one being taken into account. These places are determined when carrying out additional measurements in vertical
gradients of the EMF with the use of scalar magnetometers at the gauge length of 6 km. It has been shown that the found places
can be considered as nonanomaly, if the difference of values of the anomaly EMF at the gauge length of 6 km does not exceed
1.5 nT within the profile’s portion of about 100 km in length. An experiment in nature has revealed that errors for the IGRF-2005
and IGRF-2010 models, corrected for secular variation of the EMF, can reach 200 and 140 nT, respectively, within the limits
of the territory where the Kama-Emba magnetic anomaly is located; these errors are determined by the considered causes. Comparison
of aerostatic profiles of magnetic anomalies with data on the anomaly EMF, derived from the maps, has shown that the realizations
derived from the maps contain overestimated negative values of the anomaly EMF, because they reflect processes in the near-surface
layer of the Earth’s crust. This fact causes the situation when attempts to recalculate the anomaly EMF into the upper half-space
by the near-surface data still have not been successful. Only realizations derived at the altitudes comparable to the thickness
of the Earth’s crust can give an adequate model of the anomaly EMF in the circumterrestrial space and enable us to recalculate
magnetic anomalies reliably into any altitude levels. 相似文献
10.
The spectral AOD measurements have been made for the first time over Patiala during multi-platform field campaign ICARB—2006 using a Multi-Wavelength Radiometer (MWR) along with the suspended particulate matter measurements with a high volume sampler. Spectral AOD has higher values in May in comparison to March and April. The monthly mean AOD values at 500 nm are 0.26 ± 0.08, 0.36 ± 0.19 and 0.58 ± 0.20 for the months of March, April and May respectively. The mean AOD is more during afternoon in comparison to forenoon at all wavelengths. The atmospheric turbidity is higher in May and is attributed to dust transported by southerly winds prevailing during this month. The Ångström parameter α varies between zero and 0.68 while β ranges from 0.1 to 0.9. The columnar water vapour content ranges from 0.12 to 2.92 cm, having a mean value of 1.06 ± 0.648 cm. The mean total suspended particulate matter is 334.41 ± 97.56 μgm/m3, an indication of high aerosol loading over Patiala during the campaign period. 相似文献
11.
S K PAL JITENDRA VAISH SAHADEV KUMAR ABHAY KUMAR BHARTI 《Journal of Earth System Science》2016,125(1):165-178
The present study deals with the coal fire mapping of East Basuria Colliery, Jharia coalfield, India, using the magnetic method. It is based on the fact that rise in temperature would result significant changes in magnetic susceptibility and thermo-remanent magnetization (TRM) of the overlying rocks. Magnetism increases slowly with the rise of temperature until the Curie temperature. Generally, rock/ overburden loses magnetization and becomes paramagnetic due to heating to Curie temperature, which results with significant reduction in magnetic susceptibility. However, magnetism increases significantly after cooling below the Curie temperature. Several data processing methods such as diurnal correction, reduction to pole (RTP), first and second vertical derivatives have been used for analysis of magnetic data and their interpretation. It is observed that the total magnetic field intensity anomaly of the area varies approximately from 44850 to 47460 nT and the residual magnetic anomaly varies approximately from ?1323 to 1253 nT. The range of the magnetic anomaly after RTP is approximately 1050–1450 nT. About 20 low magnetic anomaly zones have been identified associated with active coal fire regions and 11 high magnetic anomaly zones have been identified associated with non-coal fire regions using vertical derivative techniques. 相似文献
12.
Jean-Louis Le Mouël Pierre-Noël Mayaud Peter Shebalin 《Comptes Rendus Geoscience》2003,335(13):935-941
Big perturbations of the magnetic field (amplitudes larger than 250 nT) are simply detected by subtracting the values of a model from the measurements of CHAMP satellite. Taking a full year of CHAMP data and organizing them in four subsets of three months length (spring, summer, autumn, winter), it is found that: (a) the two domains where such big perturbations mainly exist are limited, in both hemispheres, by a parallel of high latitude of the corrected geomagnetic coordinates system; (b) a conspicuous seasonal (annual) variation affects the density of the perturbations and is opposite in the two hemispheres. We hold that these perturbations are linked to the midday magnetic activity within the auroral zone, long ago described by one of us (Mayaud, 1956). The source of the perturbations observed at the satellite altitude would be field-aligned currents resulting from the penetration of the solar wind into the magnetospheric cusps. To cite this article: J.-L. Le Mouël et al., C. R. Geoscience 335 (2003). 相似文献
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D. D. Khandelwal Vineet Gahalaut Naresh Kumar Bhaskar Kundu Rajeev Kumar Yadav 《Natural Hazards》2014,74(3):1853-1861
We report GPS measurements of continuous observations from the multi-parametric geophysical observatory (MPGO) at Ghuttu, Garhwal Lesser Himalaya. Other than the evidence of secular motion depicting strain accumulation due to locking of the underneath seismically active detachment, measurements at Ghuttu show annual variation of ±4 mm on horizontal component. Such variations are more prominent in the north coordinate and do not directly correlate with the meteorological parameters such as variations in rainfall, water table, and atmospheric pressure measured at the MPGO observatory. These variations are also not the artefact of data processing and network. They correlate with the water load storage in the Ganga plains, with minimum in displacement coinciding with the maximum storage of water in Ganga plains immediately after the monsoon and vice versa. Such variations also appear to cause annual variation in the low-magnitude earthquake frequency in the Himalayan region, being relatively more in the winter period. 相似文献
15.
E. N. Vinyaikin 《Astronomy Reports》2007,51(7):570-576
Radio flux measurements of the Crab nebula have been performed over many years relative to Orion A at 927 MHz and relative to Cygnus A and Virgo A at 151.5 MHz. The inferred average secular rates of decrease in the radio flux of the Crab nebula are d 927 MHz = ?0.18 ± 0.10% yr?1 over 1977–2000 and d 151.5 MHz = ?0.3 ± 0.1% yr?1 over 1980–2003. The weighted mean flux-decrease rate averaged over several years of relative measurements at 86, 151.5, 927, and 8000 MHz is d mw = ?0.17 ± 0.02% yr?1. The secular flux decrease is frequency independent, with an upper limit of |dα/dt| < 3 × 10?4 yr?1 for the absolute value of the rate of change of the spectral index, and remains constant in time when averaged over long time intervals. The results of our measurements at 151.5 and 927 MHz combined with published absolute measurements at 81.5 and 8250 MHz are used to determine the radio spectrum of the Crab nebula for epoch 2010.0. 相似文献
16.
C. R. Burn 《第四纪科学杂志》1988,3(1):31-38
An examination of soil thermal and hydrologic regimes at several sites near Mayo, Yukon Territory, and the ground-ice stratigraphy of a thaw-slump headwall close to these sites supports the hypothesis that an ice-rich zone, frequently observed at the base of the active layer, may be due to the annual water balance of permafrost. Observations demonstrate that ice lenses have grown at the top of permafrost in soil tubes installed in 1983. In addition, 90 cm of segregated ice are exposed in the thaw-slump headwall above a thaw unconformity, dated at 8870 ± 200 years BP, but below the base of the present active layer. These data suggest that the rate of water incorporation into permafrost over the last 8000 years in the Mayo area has been at least 0.1 mm yr?1. 相似文献
17.
Extensive work on the palaeomagnetism of the Deccan traps by several workers has revealed only one reversal (normal-reverse-normal)
of the geomagnetic field during the period of eruption of these flows. The scatter in the natural remanent magnetic directions
of different flows in a sequence of these traps is rather large and it persists even after magnetic cleaning. Generally this
large scatter of directions is attributed to the geomagnetic secular variation during formation of the traps. Recent studies
of the magnetic properties of the trap samples indicate that the presence of multidomain magnetite in a lava sequence differs
from locality to locality in the Deccan trap province and so the stability of their natural remanent magnetization. While
these features can be clearly perceived, an understanding of the same seems to be quite difficult. However, it appears that
part of the scatter in directions could be due to the alteration of the magnetic minerals in the Deccan traps and hence it
would not be proper to relate the entire scatter to the secular variation. 相似文献
18.
A. V. Mordvinov 《Astronomy Reports》2006,50(11):936-943
The asymmetry of the magnetic field of the Sun and its manifestation in the interplanetary magnetic field (IMF) are studied. The dominant magnetic polarity of the radial component of the IMF alternates from cycle to cycle, but with an overall systematic dominance of polarity directed toward the Sun. The global asymmetry is also manifest in the component of the IMF perpendicular to the plane of the solar equator. The dominance of positive values of B z together with an appreciable linear trend in the cumulative sum of this quantity is interpreted as a manifestation of a relic solar magnetic field. The strength of this relic magnetic field near the Earth is estimated to be 0.048 ± 0.015 nT, based on the growth of the linear component of the cumulative sum of B z . Time intervals, in which negative values of the B z component of the IMF dominate and enhanced geomagnetic activity is observed, are identified. Our analysis of solar and heliospheric magnetic fields in an integrated representation has enabled us to compare various types of measurements and estimate their stability. 相似文献
19.
Holger Steffen Olga Gitlein Heiner Denker Jürgen Müller Ludger Timmen 《Tectonophysics》2009,474(1-2):69
Fennoscandia is a key region for studying effects of glacial isostatic adjustment. The associated mass variations can be detected by the Gravity Recovery and Climate Experiment (GRACE) satellite mission, which observes the Earth's gravity field since April 2002, as well as by absolute gravimetry field campaigns. Since 2003, annual absolute gravity (AG) measurements have been performed in Fennoscandia by the Institut für Erdmessung (IfE, Institute of Geodesy) of the Leibniz Universität Hannover, Germany, within a multi-national cooperation. This offers a unique opportunity for validation and evaluation of the GRACE results. In this preliminary study, the GRACE results are compared to secular gravity changes based on the surveys from 2004 to 2007 with the FG5-220 gravimeter of the IfE.The results from GRACE monthly solutions provided by different analysis centres show temporal gravity variations in Fennoscandia. The included secular variations are in good agreement with former studies. The uplift centre is located west of the Bothnian Bay, the whole uplift area comprises Northern Europe. Nevertheless, the differences between the GRACE solutions are larger than expected and the different centre-specific processing techniques have a very strong effect on possible interpretations of GRACE results. The comparison of GRACE to the AG measurements reveals that the determined trends fit well with results from GRACE at selected stations, especially for the solution provided by the GFZ. Variations of land hydrology clearly influence results from GRACE and the AG measurements. 相似文献
20.
Over how much time should the geomagnetic field be averaged to obtain the mean-palaeomagnetic field?
Average geomagnetic field models are now available over six orders of magnitude in time. Models based on Present and historical, archaeomagnetic and palaeomagnetic data illustrate how the amplitudes of secular variation of nonaxial dipole terms strongly decrease as a function of averaging window, mostly when jumping from the 1-yr to the 1700-yr average. The mean archaeomagnetic field bridges the gap between the complex historical field and the far simpler palaeomagnetic field, and appears to be much closer to the latter. Confidences in average field coefficients based on statistical field models give a quantitative basis to the practice of averaging data over a few millenia in order to 'suppress secular variation'. In particular, the axial quadrupole emerges from noise when the available time series exceed about 6 kyr. This happens to be close to the timescales of excursions and reversals. It is now a priority to obtain detailed data spanning the last 50 kyr. 相似文献