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41.
We compare the results of two distinct methods for deriving photospheric vector magnetic fields from the Zeeman effect as observed in the Fe I line at 6302.5 A at high spectral resolution (45 mA.). One method ignores magneto-optical effects but allows for an absolute determination of B from the integral properties of the Stokes profiles, under the assumption of weak field strength. The other method is an iterative least-squares fitting technique developed by Lites and Skumanich which fits the observed Stokes profiles to the profiles predicted by the Unno-Rachkovsky solution to the radiative transfer equation. We find empirically that for sunspot fields above 1500 gauss the two methods agree in derived azimuthal and inclination angles to within ± 20 degs., Furthermore, for such fields, the estimate of the line of sight field and the transverse field derived using the two methods agree to within ± 500 gauss. In weak field strength regions the integral method can be used with little error and computational load in the estimation of the line of sight field, the transverse field and the inclination angle but the disagreement in derived azimuthal angle is considerable ( ± 90 degs.). 相似文献
42.
Antithetic fault linkages in a deep water fold and thrust belt 总被引:4,自引:0,他引:4
Simon Higgins Richard J. Davies Benjamin Clarke 《Journal of Structural Geology》2007,29(12):1900-1914
Deep water fold and thrust belts consist of both forethrusts and backthrusts that can link along strike to form continuous folds in the overburden. The interaction of faults of opposing dip are termed ‘antithetic thrust fault linkages’ and share the common feature of a switch in vergence of overlying hangingwall anticlines. Using three-dimensional seismic data, on the toe-of-slope of the Niger Delta, linkages are classified into three distinct structural styles. This preliminary classification is based on the vertical extent of faulting within a transfer zones relative to the branch line of the antithetic faults. The stratigraphic level of the lateral tip of the fault, the shape of lateral tip region of a fault plane and the stratal deformation within the transfer zones is also distinctive in each type of fault linkage. A Type 1 linkage comprises faults that overlap exclusively above the level of the branch line. A ‘pop-up’ structure forms within the transfer zone with sediments below remaining planar. The lower tip lines of faults climb stratigraphically towards the linkage zone creating asymmetric, upward-tapering lateral tip regions. In Type 2 linkages fault overlap occurs lower than the level of the branch line such that lateral fault tips are located within the footwall of the counterpart fault. Faulting is thus limited to the deeper section within the transfer zone and creates unfaulted, symmetric, bell-shaped folds in the overburden. Upper tip lines of faults lose elevation within the transfer zone creating asymmetric, downwards-tapering lateral tip regions. In Type 3 linkages both faults continue above and below the branch line within the transfer zone resulting in cross-cutting fault relationships. Horizon continuity across the folds, through the transfer zones, varies significantly with depth and with the type of fault intersection. 相似文献
43.
The suggestion that the Moon's magnetic field is due to adiabatic magnetohydrodynamic convection of a molten core has been made by a number of recent authors. Considerations based on petrology, mass and rotational inertia limit the size of this hypothetical core to a few 100 km at the most. A proposal has been made that this core is either molten iron or iron sulfide. Fortunately, we know the properties of both molten iron and iron-sulfide at lunar core pressures. We can find no way of maintaining circulation in a hypothetical lunar core, as circulation is contingent upon a temperature gradient being greater than the adiabatic gradient, or an internal heat source. 相似文献
44.
Colin A. Ronan 《Geophysical Journal International》1968,15(1-2):241-248
45.
Heat flowing out of the core must flow into the mantle. If the Earth's magnetic field is owing to adiabatic magnetohydrodynamic circulation of the outer core, whole mantle convection or melting at the core mantle boundary is required to keep the inner core from becoming isothermal, thereby preventing adiabatic circulation.Alternatively, the outer core fluid must have some unexpected and exotic property such as an extremely low coefficient of thermal expansion and resultant low Gruneisen's parameter.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April 1973. Publication No. 1046 Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Calif., U.S.A. 相似文献
46.
Ronan Pavic Martin G. Koller Pierre-Yves Bard Corinne Lacave-Lachet 《Journal of Seismology》2000,4(1):59-77
An assessment of uncertainties for ground motion predictions with the aid of the empirical Green's function (EGF) technique is presented. The main input parameters were identified, and their respective uncertainties were assessed by means of an international expert inquiry. The repercussion of these input uncertainties on the final ground motion estimates were investigated by means of the Latin Hypercube Sampling technique. The mean ground motion estimates (response spectra) and their standard deviations were compared with results obtained from empirical attenuation laws. The most sensitive input parameter turned out to be the seismic moment corresponding to the EGF. In general, if the source parameters are well determined, equivalent uncertainties, statistically speaking, can be expected from the EGF technique and from the application of attenuation laws. Therefore, if EGFs with well known source parameters are available, the EGF technique seems to be preferable: site effects are automatically taken into account, and physically realistic acceleration time histories can be obtained. However, further investigations on the reliability of the EGF technique should be performed, and finally, it is recalled that the EGF technique is based on the assumption of linearity. If conditions are such that this assumption cannot be maintained, the EGF technique should be combined with non-linear geotechnical methods. 相似文献
47.
Soren M. Newman Matthew S. Carroll Pamela J. Jakes Daniel R. Williams Lorie L. Higgins 《社会与自然资源》2014,27(11):1161-1176
Wildfire is one of several potential disturbances that could have extraordinary impacts on individuals and communities in fire-prone areas. In this article we describe disturbance risk perceptions from interviews with residents in three Florida communities that face significant wildfire and hurricane risk. Although they live in areas characterized by emergency managers as having high wildfire risk and many participants have direct experience with wildfire, residents tended to share high hurricane and low wildfire risk perceptions. The different perceptions of risk seem linked to several factors: direct hurricane experience, different scales of impact, the local “hurricane culture,” effectiveness of local ordinances and development patterns, perceived predictability of the event, and perceived ability to control the event. This study shows that residents may perceive and act to reduce risk for one disturbance in relation to their perceptions, concern, and actions for another. 相似文献
48.
The role of collisions between extragalactic jets and dense clouds in determining the appearance of high-redshift radio galaxies is discussed and investigated through numerical hydrodynamic simulations in three dimensions. The code has the facility to track jet material separately from ambient material. This allows us to use simplifying assumptions to calculate synthetic radio images. The results indicate that the most powerful radio sources are likely to be observed during or shortly after an interaction, and that such interactions can explain both the radio structures and the spatial association between optical and radio light found in powerful radio galaxies. In some cases such a scenario may provide an alternative explanation of jet properties to mechanisms based on variations in the source or fluid-dynamical instabilities.This author is supported by a PPARC research studentship 相似文献
49.
Solar Physics - We compare the results of two distinct methods for deriving photospheric vector magnetic fields from the Zeeman effect as observed in the Fe I line at 6302.5 A at high spectral... 相似文献
50.
Matthieu?AngeliEmail author Jean-Philippe?Bigas David?Benavente Beatriz?Menéndez Ronan?Hébert Christian?David 《Environmental Geology》2007,52(2):205-213
The objective of this study is to understand and predict the alteration of porous rock by crystallization of salts. Samples
of different rocks have been tested according to the EN 12370 standard test. Two parameters are proposed to evaluate the alteration
of a rock during these tests. The alteration index AI represents the cycle in which the first damages occur. The alteration
velocity AV represents the alteration rate at the end of the experiment, when the decay has become regular. These parameters
can be estimated with the help of a microstructural study of the rocks. The most relevant intrinsic parameters of the stones
for this estimation are capillary coefficient, evaporation coefficient, tensile strength and P-waves velocity. An evaluation
of the alteration pattern is also proposed depending on the eventual heterogeneities and anisotropies of the rocks. The influence
of the dimension and shape of the samples is also discussed. 相似文献