首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 78 毫秒
1.
Fundamental-mode Rayleigh wave attenuation data for stable and tectonically active regions of North America, South America, and India are inverted to obtain several frequency-independent and frequency-dependentQ models. Because of trade-offs between the effect of depth distribution and frequency-dependence ofQ on surface wave attenuation there are many diverse models which will satisfy the fundamental-mode data. Higher-mode data, such as 1-Hz Lg can, however, constrain the range of possible models, at least in the upper crust. By using synthetic Lg seismograms to compute expected Lg attenuation coefficients for various models we obtained frequency-dependentQ models for three stable and three tectonically active regions, after making assumptions concerning the nature of the variation ofQ with frequency.In stable regions, ifQ varies as , where is a constant, models in which =0.5, 0.5, and 0.75 satisfy fundamental-mode Rayleigh and 1-Hz Lg data for eastern North America, eastern South America, and the Indian Shield, respectively. IfQ is assumed to be independent of frequency (=0.0) for periods of 3 s and greater, and is allowed to increase from 0.0 at 3 s to a maximum value at 1 s, then that maximum value for is about 0.7, 0.6, and 0.9, respectively, for eastern North America, eastern South America, and the Indian Shield. TheQ models obtained under each of the above-mentioned two assumptions differ substantially from one another for each region, a result which indicates the importance of obtaining high-quality higher-mode attenuation data over a broad range of periods.Tectonically active regions require a much lower degree of frequency dependence to explain both observed fundamental-mode and observed Lg data. Optimum values of for western North America and western South America are 0.0 if is constant (Q is independent of frequency), but uncertainty in the Lg attenuation data allows to be as high as about 0.3 for western North America and 0.2 for western South America. In the Himalaya, the optimum value of is about 0.2, but it could range between 0.0 and 0.5. Frequency-independent models (=0.0) for these regions yield minimumQ values in the upper mantle of about 40, 70, and 40 for western North America, western South America, and the Himalaya, respectively.In order to be compatible with the frequency dependence ofQ observed in body-wave studies,Q in stable regions must be frequency-dependent to much greater depths than those which can be studied using the surface wave data available for this study, andQ in tectonically active regions must become frequency-dependent at upper mantle or lower crustal depths.On leave from the Department of Geophysics, Yunnan University, Kunming Yunnan, People's Republic of China  相似文献   

2.
Summary On the basis of investigating 10 storms (1965–1967) good correlation was found between the density of the solar wind energy (2=1/2mNv2) and the intensity of the main phase of the geomagnetic storms, expressed in terms of the maximum decrease of the horizontal intensity (B=H/cos). The relation between 2, or Nv2, and B could then be used to determine the quantities and 0 ( is the factor expressing the increase in energy density in the magnetosphere, 0 is the energy density of the particles in a quiet magnetosphere). A comparison with the directly observed distribution of the energy density of the particles in the magnetosphere indicates that the computed value of 0 seems to be realistic. The magnitude of the factor will have to be checked again.  相似文献   

3.
FollowingDmitriev (1960) a rigorous theoretical solution for the problem of scattering by a perfectly conducting inclined half-plane buried in a uniform conductive half-space has been obtained for plane wave excitation. The resultant integral equation for the Laplace transform of scattering current in the half-plane is solved numerically by the method of successive approximation. The scattered fields at the surface of the half-space are found by integrating the half-space Green's function over the transform of the scattering current.The effects of depth of burial and inclination, of the half-plane on the scattered fields are studied in detail. An increase in the depth of burial leads to attenuation of the fields. Inclination introduces asymmetry in the field profiles beside affecting its magnitude. Depth of exploration is greater for quadrature component. An interpretation scheme based on a phasor diagram is presented for the VLF-EM method of exploration for rich vein deposits in a conductive terrain.List of symbols x, y, z Space co-ordinates - Half-space conductivity - 0 Free-space permeability - Excitation frequency (angular) - T Time - h Depth of the half-plane - a Inclination of the half-plane - E x x-Directed total electric field - E x p x-Directed primary electric field - E xo p x-Directed primary electric field atz=0 directly over the half-plane - H y y-Component of total magnetic field - H y p y-Component of primary magnetic field - H y0 p y-Component of primary magnetic field atz=0 directly over the half-plane - H z z-Component of total magnetic field - H z p z-Component of primary magnetic field - J x Surface density ofx-directed scattering current - G Green's function - k 0,K Wave numbers - u,u 0,u 1,u 2 Functions - Space co-ordinate - s Variable in transform domain - Variable of integration - Normalized scattering current - Laplace transform of - N Normalized - , 0, 1, 2 Functions - t Variable of integration - Skin depth - H Total magnetic field - H p Primary magnetic field - H 0 p Primary magnetic field atz=0 directly over the half-plane - M,Q,R,S,U,V Functions - N 1,N 2 Functions  相似文献   

4.
Summary Measuring, with the aid of two filters, the instantaneous intensity of the solar radiation in two wave lengths ( B = 0.44 , R = 0.64 ) by means of a sun photometer designed byVolz, we carried out determinations of the decadic turbidity coefficientB (=0.5 ) and the wave length exponent of the haze extinction for Mexico City. Observations were made for almost two and a half years (1960 to 1962 period). A seasonal size distribution in both parameters was found. Although the data thus obtained are provenient of a contaminated atmosphere, comparison of our data is made with those found for higher latitudes ofÅngström, Schüepp andVolz. The height of the homogeneous haze layerH D was calculated showing pronounced variations for a given wind direction. The maximum and minimum values ofB enable us to get, by the first approximation, the aerosol size distribution ofJunge for our latitudes. However, for exceptional very clear days having maximum actinometric intensity of the solar radiation the sensitivity of the microamperimeter in theVolz sun photometer fails.  相似文献   

5.
Summary The equations of motion for the free oscillations of a heterogeneous spherical earth model are derived. It is found that the lateral variations of density and elastic moduli couple the odd(even) harmonics of the spheroidal oscillations with themselves as well as with the even (odd) harmonics of the torsional oscillations.List of symbols r, , Spherical coordinates;r is the radial distance from earth's center, is the co-latitude, and is the east longitude - r Space vector denoting a point with coordinatesr, , and - Gradient operator - 2 Laplacian operator - ij Kronecker's delta function - I Identity matrix - i   相似文献   

6.
This work is part of an attempt to quantify the relationship between the permeability tensor (K) and the micro-structure of natural porous media. A brief account is first provided of popular theories used to relate the micro-structure toK. Reasons for the lack of predictive power and restricted generality of current models are discussed. An alternative is an empirically based implicit model whereinK is expressed as a consequence of a few pore-types arising from the dynamics of depositional processes. The analytical form of that implicit model arises from evidence of universal association between pore-type and throat size in sandstones and carbonates. An explicit model, relying on the local change of scale technique is then addressed. That explicit model allows, from knowledge of the three-dimensional micro-geometry to calculateK explicitly without having recourse to any constitutive assumptions. The predictive and general character of the explicit model is underlined. The relevance of the change of scale technique is recalled to be contingent on the availability of rock-like three-dimensional synthetic media. A random stationary ergodic process is developed, that allows us to generate three-dimensional synthetic media from a two-dimensional autocorrelation functionr( x , y ) and associated probability density function measured on a single binary image. The focus of this work is to ensure the rock-like character of those synthetic media. This is done first through a direct approach:n two-dimensional synthetic media, derived from single set ( ,r( x , y )) yieldn permeability tensorsK i-1,n i (calculated by the local change of scale) of the same order. This is a necessary condition to ensure thatr( x , y ) and carry all structural information relevant toK. The limits of this direct approach, in terms of required Central Process Unit time and Memory is underlined, raising the need for an alternative. This is done by comparing the pore-type content of a sandstone sample andn synthetic media derived fromr( x , y ) and measured on that sandstone-sample. Achievement of a good match ensures that the synthetic media comprise the fundamental structural level of all natural sandstones, that is a domainal structure of well-packed clusters of grains bounded by loose-packed pores.  相似文献   

7.
Summary The secular positive acceleration of the Earth's rotation has been computed on the basis of the observed secular decrease of the second zonal harmonic[5]. It corresponds to the observed secular deceleration of the Earth's rotation which should be greater because of oceanic tides.
¶rt; u a¶rt;a u m aauu [5], u ¶rt;a num u au. m mmmu a¶rt;a u mu au u, m.. n¶rt; n m uu , ¶rt; m n auu nuua.
  相似文献   

8.
Summary The geopotential scale factor R 0 =GM/W 0 has been determined on the basis of satellite altimetry as R 0=(6 363 672·5±0·3) m and/or the geopotential value on the geoid W 0 =(62 636 256·5±3) m 2 s –2 . It has been stated that R 0 and/or W 0 is independent of the tidal distortion of surface W=W 0 due to the zero frequency tide.
¶rt;a nmu amumuu u ama amnmuaa R 0 =GM/W 0 =(6 363 672,5±0,3) m u/uu aunmuaa a nmuu¶rt;a W 0 =(62 636 256,5±3) m2 s–2. m, m R 0 u/uu W 0 auum m nm amu a a nuu ¶rt;au nmu W=W 0 .
  相似文献   

9.
Linear stacking procedures are used to retrieve the attenuation of 91 modes belonging to the 3rd, 4th and 5th Rayleigh overtones branches in the 80–160 s period range, and contributing to the so-called PhaseX wave group. Our data show in general slightly less attenuation than expected from available models. Data space inversion shows that, when combined with previously measured fundamental modeQ's, this new dataset improves resolution significantly in the 1000–2000 km depth range. Based on this remark, we carry out a number of parameter space inversions. Our results suggest a narrow (80–200 km) zone of high attenuation (Q =75–90), low attenuation in the intermediate mantle (670–1500 km); (Q 350), and lower values in the deeper mantle (Q 200).  相似文献   

10.
u¶rt;m ¶rt; anum¶rt;-amm aamumu maum a aa nu mummu (). ma¶rt;am aamumu uu mau auma uu am auu a uu aaa aa.  相似文献   

11.
The horizontal and vertical derivative profiles of magnetic anomalies of dykes show some interesting properties. The points of zero derivatives and the points where the derivatives are equal are conjugate point pairs. A method of interpretation of dyke anomalies is suggested, which utilizes the distances between these points.Notation F Magnetic anomaly in total intensity - Z Depth to top of the dyke - 2T Width of the dyke - Geological dip of the dyke - I Effective intensity of magnetisation in the plane of profile - Dip of effective magnetisation vector in the plane of profile - Strike angle of the dyke - i Magnetic dip - Q – - Q f –+arctan (sin coti) - I f   相似文献   

12.
Summary The basic formula used in the presented paper gives the relation between the P wave travel-time perturbation and the perturbation of an inhomogeneous transversely isotropic medium, expressed by four perturbations of elastic parameters and by two angles of orientation of the axis of symmetry of transverse isotropy in space. The travel time perturbation is computed along the ray in the unperturbed inhomogeneous isotropic medium. Four elastic parameters and two angles are parametrized in the model under study and a system of equations for many rays is constructed. The equations are linear in the sought elastic parameters and nonlinear in the sought angles, and the iterative Levenberg-Marquardt algorithm is thus used to solve them. The theoretical 3-D inverse problem was solved in the presented numerical example. The data, simulating teleseismic data, were computed in the direct problem and then inverted. The results indicate the applicability and limitation of the presented algorithm in real problems.
a a, unaa n¶rt;aa am, ¶rt;am mu ¶rt; uu u na u uu ¶rt;¶rt; nn umn ¶rt;, a m nuu naamau u ¶rt; au umauu u umuu nn umnuu nmam. u u na um ¶rt; a aa ¶rt;¶rt; umn ¶rt;. nu naam u ¶rt;a a naamuua ¶rt;u u nma uma au ¶rt; u . au u n um nu naama u u n um a umauu umuu, nm un m umamu aum a-aa¶rt;ma ¶rt; u u. am nu¶rt; ¶rt; m u nu. nu muu ¶rt;a aaa a na a¶rt;aa u am ¶rt;a a. mam naam auu u mu nuu nu¶rt;uma a a.
  相似文献   

13.
Summary Relations for the direct transformation of the Cartesian coordinate system into a system of geodetic coordinates.
u ¶rt;u , , z ¶rt;uu , , h.
  相似文献   

14.
Summary Magnetic variations were recorded along three profiles crossing the southeastern margin of the Bohemian Massif. The data were processed in order to get induction vectors (Wiesevectors) and in-phase and out-of-phase induction vectors (Schmucker-vectors). Several events of field variations were separated into external and internal parts. The same events were also treated by a physical-statistical approach. Taking into account these results, we were able to delineate a zone of electrical inhomogeneity. It is in close relation to the Moravo-Silesian lineament. The depth of the internal anomalous field source was estimated at 20 to 25 km.
¶rt;a u uuau n uu n nu, nu — u. u¶rt;uu ( u), n u u n¶rt; u n u¶rt;uu ( ), n ¶rt;u n uau u u u n au ¶rt; uu-uuu ¶rt; u ¶rt;¶rt;u na¶rt; nu -uu . ¶rt; au uu a n a u n¶rt; 20–25 .
  相似文献   

15.
Summary The occurrence zone of the VLF chorus in the upper ionosphere appears at L-shells lower than plasmapause position Lpp; with increasing geomagnetic activity the spatial dimension of the zone diminishes, its upper boundary being shifted in correspondence with the plasmapause position, the lower remaining practically without change(L=2.0÷2.5). Calculations of propagation paths have shown that the similarity of the VLF chorus spectrum at different upper-ionospheric latitudes as well as the large spatial dimension of the zone of observation can be explained as special features in the propagation of VLF waves from an equatorial source, starting in the vicinity of the plasmapause with different initial normal angles.
a umauu u ana amu L-, u Lpp (Lpp — nu nana); uu aum amumu nmam a am, nu aua am mmmuu uu nu nana, a u mam namuu u(L=2.0÷2.5). am mamu naam, m n¶rt;u nm a au uma u, ma a nmam ama a¶rt;u, m m mu anmau m amua umua, an amu nana, uu au au.
  相似文献   

16.
Summary Simple linear representation of the components of an approximate plane solution of point mass loading of the Earth's surface in a conveniently chosen coordinate system leads to selection of a 2nd-degree curve which is the best fit of the spherical solution for the given Earth model. The new approximate solution, which, analogously to the plane solution, can be called a parabolic solution, enables the simple input parameters of the plane solution to be used also for substantially larger angular distances. The comparison with the spherical solution is carried out by computing the effects of the M2-wave of ocean tides. The results of the computations for the tidal station Brussels prove the two solutions to be in sufficient agreement for global problems as well.
m nu uau aa nuuum nm u m m au nmu u n¶rt;¶rt; um ¶rt;uam ¶rt;m ma u m mnu, ma auu a n¶rt;¶rt;um u u ¶rt; ¶rt;a ¶rt;u u. nuuum u, m n aauu nm u aam naauu u, nm unam nm ¶rt; ¶rt;a nm u ¶rt;a ¶rt; m u amu. au uu u m uu uu 2 u nuu. mam uu ¶rt; nuu mauu ¶rt;aam ¶rt;mum au u u ¶rt;a ¶rt;a a¶rt;a.
  相似文献   

17.
Summary Radiation absorption by water vapour plays an important role in the physics of the atmosphere. The calculation of the absorbed radiation energy by water vapour requires the amount of precipitable water in the atmosphere to be known. Actinometric and aerological measurements were used to establish the relation between vapour pressure and absorbed solar radiation.
u a¶rt;uauu ¶rt; nam uam a amu uuu am. uu n a¶rt;uauu ¶rt; na a¶rt; am m a¶rt; ¶rt; am. u¶rt; mu ¶rt; ¶rt;au ¶rt; naa u n a¶rt;uau a amu muu u auu uu.
  相似文献   

18.
Zusammenfassung Die Gleichgewichtsfiguren lassen sich gänzlich unabhängig vom Dichtegesetz durch die Eingeschaft charakterisieren, daß der Absolutbetrag des Formparametersf0 ein Minimum sein muß. Diese merkwürdige Eigenschaft liefert eine Gleichung zwischen der geometrischen Abplattung und den beidenStokesschen Konstanten und , mit deren Hilfe aus den 4 Lösungen desHelmertschen Gleichungssystems für eine bestimmte Masse die 3 Gleichgewichtsfiguren ausgesiebt werden können. Jede beliebige heterogene sphäroidische Gleichgewichtsfigur ist entweder durch die Masse und die Gestalt ihrer freien Oberfläche oder durch die Masse und drei physikalische Parameter gänzlich eindeurig bestimmt; sie hat ein streng individuelles Dichtegesttz. Aus der dreifach unendlichen Mannigfaltigkeit der Gleichgewichtsfiguren können linear Reihen herausgegriffen werden, indem man entweder zwei physikalische Parameter festhält oder indem man die Figuren aufsucht, welche eine gegebene Fläche zur gemeinsamen äußeren Niveaufläche besitzen oder die Reihe jener Gleichgewichtsfiguren, die sich aus der Schar der äußeren Niveauflähen einer gegebenen Gleichgewichtsfigur bilden läßt.Obwohl das HauptträgheitsmomentC keineStockessche Konstante ist, kann das durch ,W 0 undC eindeutig definierte Normalsphäroid der Erde hypothesenfrei bestimmt werden, weil in der Reihe (,K) auch die Trägheitsmomente und damit die dynamische Abplattung konstant ist. Damit kann die empirisch bekannte dynamische Abplattung mittels des Rückganges auf die homogene Ausgangsfigur der Reihe (,K) durch die statische Abplattung ersetzt werden. Allerdings muß der Ableitung des Normalsphäroides an Stelle der primär unbekannten Werte für die Erdmasse und den Potentialwert des Geoides die Äquatorschwere und die Äquatorachse zugrunde gelegt werden.Abschließend werden noch die drei linearen Reihen (,W 0), (,K) und (W 0,K) diskutiert, welche sich im Normalsphäroid schneiden müssen. Auch kann in dem mit den Achsena, undh m gebildeten Koordinatensystem die Hüllfläche der Gleichgewichtsfiguren angegeben werden; sie ist durch den Formparameterf=–3a2/2 gekennzeichnet.
Summary The figures of equilibrium independant from the law of density in their interior can be characterized by the remarkable property that the absolute value of the «shape-parameter» must be a minimum. This gives an equation between the flattening and the twoStokes constant and , by which the 3 figures of equilibrium can be selected from the 4 solutions ofHelmert's equations for a given mass. Each inhomogeneous spheroidical figure of equilibrium is determined unequivocally by the mass and the shape of its free surface or by the mass and three physical parameters; the law of density is strictly individual. From the threefold infinite multiplicity of the figures of equilibrium linear series are to find out with two fixed physical parameters or you can compute a series of figures with a common level surface or the series built by all level surface of a given figure of equilibrium.Though the moments of inertia are notStokes constants the normal spheroid of earth unequivocally defined by ,W 0 andC can be determined without hypotheses, because in the series (,K) also the moments of inertia and the mechanical ellipticity are constant. Therefore the empirically known mechanical ellipticity can be substituted by the static flattening returning to the homogenous figure in the beginning of the series. Of course the determination of the normal spheroid of earth demands the knowledge of gravity in equator and of the equator-axis instead of the unknown mass of earch series (,W 0), (,K) and (K,W 0), which intersect in the normal spheroid, are discussed. Also the boundary surface of the figures of equilibrium in the Cartesian system of the coordinatesa, andh m is discussed; this surface is determined byf=–3a2/2.
  相似文献   

19.
Summary Secular non-tidal variations of geopotential and gravity are estimated due to secular decrease of the second zonal geopotential harmonic, secular polar motion and deceleration of the Earth's rotation.
am a nuu uunmuaa u u u mmu, a u m aauunmuaa, ¶rt;uu n u u mu au u.
  相似文献   

20.
Summary Rotatory vibrations of a thick spherical shell of isotropic non-homogeneous material with rigidity and density given by (i) = 0 r -2 withQ =Q 0 r -2 e 2mr and (ii) = 0 r m with =Q 0 r n have been discussed and the frequency equation is derived with numerical enumeration of frequency in each case.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号