Geophysical Journal International

McMullen, Richard, J.;Mohraz,, Bijan

doi: 10.1111/j.1365-246X.1987.tb06646.xpmid: N/A

Summary An axisymmetric finite element was used to model the lithosphere as an infinite, 40 km-thick, circular, elastic plate on an elastic foundation (asthenosphere) subjected to concentrated thermal loading. Thermal loading is produced by a point heat source of 4.184 × 108 watts located 60 km beneath the plate, within the asthenosphere. Increased nodal temperatures within the lithospheric finite element mesh were obtained from a solution to the steady-state heat conduction equation for a point source in a semi-infinite half-space. Vertical as well as radial thermal expansion coefficients of 1.33 × 10-5 K-1 were utilized in the solutions. Thermoelastic loads as well as isostatic uplift forces are applied as nodal loads in the finite element lithosphere model. Thermoelastic loads are produced from uneven heating of the lithosphere and differential expansion. Isostatic uplift forces result from radial expansion and the diminished density of heated lithosphere columns. Uplift of the lithosphere due to the point heat source and vertical expansion is reduced because of radial expansion and flexure. This occurs because material at the base of the lithosphere is closer to the point heat source and experiences greater radial expansion. For sediment infill, thermoelastic loading reduces the surface uplift produced by isostatic uplift forces from 311 to 192 m. Thermoelastic lithosphere models yield significantly higher radial stress profiles than density models without thermoelastic stresses. The neutral plane for radial stress is displaced towards the surface in the thermoelastic models due to greater radial expansion of basal lithosphere material which is closer to the point heat source. The finite element model has several advantages over the classical thin plate approach. Stresses and strains can be evaluated at any point within the lithosphere. This capability was used in this study to determine vertical lithosphere expansion (thickening), non-linear variation of stress with depth, and the stress neutral plane position. Thermoelastic loads produce significant stresses and deformations in the lithosphere. Thermal loads should be considered in addition to gravity loads in elastic lithosphere flexure models for basin formation, rifting, and volcanic surface loading. lithosphere, finite element, thermoelastic, axisymmetric, flexure References Bathe K. J. Wilson E. L. Peterson F. E. , 1973 . SAP IV — A structural analysis program for static and dynamic response of linear systems , College of Engineering, University of California at Berkeley , Report No. EERC, 73 – 11 . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Birch F. S. , 1975 . Conductive heat flow anomalies over a hotspot in a moving medium , J. geophys. Res. , 80 , 4825 – 4827 . Google Scholar Crossref Search ADS WorldCat Bills B. G. , 1983 . Thermoelastic bending of the lithosphere: Implications for basin subsidence , Geophys. J. , 75 , 169 – 200 . Google Scholar Crossref Search ADS WorldCat Bott M. H. P. , 1981 . Crustal doming and the mechanism of continental rifting , Tectonophys. , 73 , 1 – 8 . Google Scholar Crossref Search ADS WorldCat Carslaw H. S. Jaeger J. C. , 1959 . Conduction of Heat in Solids , Oxford University Press . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Crough S. T. , 1978 . Thermal origin of mid-plate hotspot swells , Geophys. J. , 55 , 451 – 469 . Google Scholar Crossref Search ADS WorldCat Davis E. E. Lister C. R. B. , 1974 . Fundamentals of ridge crest topography , Earth Planet. Sci. Lett. , 21 , 405 – 413 . Google Scholar Crossref Search ADS WorldCat DeRito R. F. Cozzarelli F. A. Hodge D. S. , 1983 . Mechanism of subsidence of ancient cratonic rift basins , Tectonophys. , 94 , 141 – 168 . Google Scholar Crossref Search ADS WorldCat Gass I. G. Chapman D. S. Pollack H. N. Thorpe R. S. , 1978 . Geological and geophysical parameters of mid-plate volcanism , Phil. Trans. R. Soc. A , 288 , 581 – 597 . Google Scholar Crossref Search ADS WorldCat Haxby W. F. Turcotte D. L. Bird J. M. , 1976 . Thermal and mechanical evolution of the Michigan Basin , Tectonophys. , 36 , 57 – 75 . Google Scholar Crossref Search ADS WorldCat Mareschal J. C. , 1981 . Uplift by thermal expansion of the lithosphere , Geophys. J. , 66 , 535 – 552 . Google Scholar Crossref Search ADS WorldCat McMullen R. J. Hodge D. S. Cozzarelli F. A. , 1981 . A technique for incorporating geothermal gradients and non-linear creep into lithospheric flexure models , J. geophys. Res. , 83 , 1745 – 1753 . Google Scholar Crossref Search ADS WorldCat McMullen R. J. Mohraz B. , 1984 . Thermoelastic stresses and rift topography: A finite element model (Abstract), EOS , Trans. Am. geophys. Un. , 65 , 1114 . OpenURL Placeholder Text WorldCat Parker R. L. Oldenburg D. W. , 1973 . Thermal model of ocean ridges , Nature , 242 , 137 – 139 . Google Scholar Crossref Search ADS WorldCat Parsons B. Sclater J. G. , 1977 . An analysis of the variation of ocean floor bathymetry and heat flow with age , J. geophys. Res. , 82 , 803 – 827 . Google Scholar Crossref Search ADS WorldCat Sleep N. H. , 1971 . Thermal effects of the formation of Atlantic continental margins by continental breakup , Geophys. J. , 24 , 325 – 350 . Google Scholar Crossref Search ADS WorldCat Sleep N. H. Snell N. S. , 1976 . Thermal contraction and flexure of mid-continent and Atlantic marginal basins , Geophys. J. , 45 , 125 – 154 . Google Scholar Crossref Search ADS WorldCat Turcotte D. L. Oxburgh E. R. , 1973 . Mid-plate tectonics , Nature , 244 , 337 – 339 . Google Scholar Crossref Search ADS WorldCat Watts A. B. Cochran J. R. , 1974 . Gravity anomalies and flexure of the lithosphere along the Hawaiian-Emperor seamount chain , Geophys. J. , 38 , 119 – 141 . Google Scholar Crossref Search ADS WorldCat This content is only available as a PDF.

Korn,, Michael

doi: 10.1111/j.1365-246X.1987.tb06647.xpmid: N/A

Summary A method for the computation of complete synthetic seismograms in vertically inhomogeneous media is presented. It is based on the combination of integral transforms and numerical techniques. The wavenumber responses of the medium are calculated in the frequency domain by an implicit second-order finite-difference scheme. This is in contrast to the Alekseev—Mikhailenko method (AMM), where numerical techniques are used to compute time-dependent wavenumber responses. Therefore the new method can be regarded as a frequency domain version of AMM. The use of numerical techniques provides an alternative to other methods such as the reflectivity method, if models with extremely complicated velocity depthfunctions are considered, or if wavefields from extended sources have to be computed or if both source and receivers are located at arbitrary depths. The frequency domain calculation has the advantage that dissipation of seismic energy due to arbitrary absorption laws is easily included. Furthermore, grid dispersion which is a major shortcoming of AMM is avoided nearly completely by the use of a special grid in which the local depth increment is proportional to the local velocity and inversely proportional to the frequency. The only error of the FD-scheme then is the dependence of the phase velocity on the propagation angle. For SH-waves a prewarping of the wavenumbers can be applied which reduces the error further. Numerical tests show that the frequency domain FD-method yields more accurate results with less computing time than AMM. As an application of the method, long-period wave propagation through earth models with random perturbation of the velocity and density depth-functions is computed. The synthetic seismograms show coda waves comparable to observed data only if the average perturbation is about two-to-four per cent. synthetic seismograms, finite differences, horizontally stratified half-space, random layering, scattering References Aki K. E. Richards P. G. , 1980 . Quantitative Seismology — Theory and Methods ( 2 vols ), Freeman , San Francisco . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Alekseev A. S. Mikhailenko B. G. , 1976 . The solution of Lamb's problem for a vertically inhomogeneous elastic halfspace (in Russian) , Izv. Akad. Nauk SSSR , Fizika Zemli , 12 , 11 – 25 . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Alekseev A. S. Mikhailenko B. G. , 1979 . Numerical Modelling of Transient Wave Fields in Seismology and Seismic Prospecting ( 2 vols ), The Siberian Branch of the Academy of Sciences of the USSR , Novosibirsk. Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Alekseev A. S. Mikhailenko B. G. , 1980 . The solution of dynamic problems of elastic wave propagation in inhomogeneous media by a combination of partial separation of variables and finitedifference methods , J. Geophys. , 48 , 161 – 172 . OpenURL Placeholder Text WorldCat Ascher U. Spudich P. , 1986 . A hybrid collocation method for calculating complete theoretical seismograms in vertically varying media , Geophys. J. R. astr. Soc. , 86 , 19 – 40 . Google Scholar Crossref Search ADS WorldCat Ben-Menahem A. Vered M. , 1973 . Extension and interpretation of the Cagniard-Pekeris method for dislocation sources , Bull. seism. Soc. Am. , 63 , 1611 – 1636 . OpenURL Placeholder Text WorldCat Bouchon M. , 1981 . A simple method to calculate Green's functions for elastic layered media , Bull. seism. Soc. Am. , 71 , 959 – 971 . OpenURL Placeholder Text WorldCat Chapman C. H. , 1978 . A new method for computing synthetic seismograms , Geophys. J. R. astr. Soc. , 54 , 481 – 518 . Google Scholar Crossref Search ADS WorldCat Cormier V. F. Richards P. G. , 1977 . Full wave theory applied to a discontinuous velocity increase: the inner core boundary , J. Geophys. , 43 , 3 – 31 . OpenURL Placeholder Text WorldCat Day S. M. Minster J. B. , 1984 . Numerical simulation of attenuated wavefields using a Padé approximant method , Geophys. J. R. astr. Soc. , 78 , 105 – 118 . Google Scholar Crossref Search ADS WorldCat Fatyanov A. G. Mikhailenko B. G. , 1979 . Numerical solution of Lamb&s problem for inhomogeneous Boltzmann medium , in Mathematical Methods for the Interpretation of Geophysical Data , pp. 115 – 160 , Academy of Sciences USSR , Novosibirsk (in Russian). Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Frankel A. Clayton R. W. , 1984 . A finite difference simulation of wave propagation in two-dimensional random media , Bull. seism. Soc. Am. , 74 , 2167 – 2186 . OpenURL Placeholder Text WorldCat Frankel A. Clayton R. W. , 1986 . Finite difference simulations of seismic scattering: implications for the propagation of short-period seismic waves in the crust and models of crustal heterogeneity , J. geophys. Res. , 91 , 6465 – 6489 . Google Scholar Crossref Search ADS WorldCat Frazer L. N. Gettrust J. F. , 1984 . On a generalization of Filon's method and the computation of the oscillatory integrals of seismology , Geophys. J. R. astr. Soc. , 76 , 461 – 481 . Google Scholar Crossref Search ADS WorldCat Fuchs K. , 1968 . The reflection of spherical waves from transition zones with arbitrary depth-dependent elastic moduli and density , J. Phys. Earth , 16 , 27 – 41 . Google Scholar Crossref Search ADS WorldCat Fuchs K. Müller G. , 1971 . Computation of synthetic seismograms with the reflectivity method and comparison with observations , Geophys. J. R. astr. Soc. , 23 , 417 – 433 . Google Scholar Crossref Search ADS WorldCat Ha J. , 1984 . Recurrence relations for computing complete P and SV seismograms , Geophys. J. R. astr. Soc. , 79 , 863 – 873 . Google Scholar Crossref Search ADS WorldCat Helmberger D. V. , 1968 . The crust-mantle transition in the Bering Sea , Bull. seism. Soc. Am. , 58 , 179 – 214 . OpenURL Placeholder Text WorldCat Kennett B. L. N. , 1974 . Reflections, rays and reverberations , Bull. seism. Soc. Am. , 64 , 1685 – 1696 . OpenURL Placeholder Text WorldCat Kennett B. L. N. , 1983 . Seismic Wave Propagation in Stratified Media , Cambridge University Press . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Kennett B. L. N. Kerry N. J. , 1979 . Seismic waves in a stratified half space , Geophys. J. R. astr. Soc. , 57 , 557 – 583 . Google Scholar Crossref Search ADS WorldCat Kind R. , 1978 . The reflectivity method for a buried source , J. Geophys. , 44 , 603 – 612 . OpenURL Placeholder Text WorldCat Kind R. Müller G. , 1975 . Computation of SV-waves in realistic earth models , J. Geophys. , 41 , 149 – 172 . OpenURL Placeholder Text WorldCat Korn M. Müller G. , 1983 . Comparison of the Alekseev-Mikhailenko method and the reflectivity method , Geophys. J. R. astr. Soc. , 72 , 541 – 556 . Google Scholar Crossref Search ADS WorldCat Korn M. Stöckl H. , 1982 . Reflection and transmission of Love channel waves at coal seam discontinuities computed with a finite difference method , J. Geophys. , 50 , 171 – 176 . OpenURL Placeholder Text WorldCat Marfurt K. , 1985 . Seismic modelling — a frequency domain/finite element approach , Annual Meeting of the Seismological Society of America , Austin, Texas . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Martynov V. N. Mikhailenko B. G. , 1984 . Numerical modelling of propagation of elastic waves in anisotropic inhomogeneous media for the halfspace and the sphere , Geophys. J. R. astr. Soc. , 76 , 53 – 63 . Google Scholar Crossref Search ADS WorldCat Menke W. Chen R. , 1984 . Numerical studies of the coda falloff rate of multiply scattered waves in randomly layered media , Bull. seism. Soc. Am. , 74 , 1605 – 1614 . OpenURL Placeholder Text WorldCat Müller G. , 1969 . Theoretical seismograms for some types of point sources in layered media — III: Single force and dipole sources of arbitary orientation , Z. Geophys. , 35 , 347 – 371 . OpenURL Placeholder Text WorldCat Müller G. , 1983 . Rheological properties and velocity dispersion of a medium with power-law dependence of Q on frequency , J. Geophys. , 54 , 20 – 29 . OpenURL Placeholder Text WorldCat Müller G. , 1985 . The reflectivity method: a tutorial , J. Geophys. , 58 , 153 – 174 . OpenURL Placeholder Text WorldCat Müller G. Schott W. , 1981 . Some recent extensions of the reflectivity method , in Identification of Seismic Sources — Earthquake or Underground Explosion , pp. 347 – 371 , eds Huseby E. S. Mykkeltveit S., Reidel , Dordrecht . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Olson A. H. Orcutt J. A. Frazier G. A. , 1984 . The discrete wavenumber — finite element method for synthetic seismograms , Geophys. J. R. astr. Soc. , 77 , 421 – 460 . Google Scholar Crossref Search ADS WorldCat Richards P. G. Menke W. , 1983 . The apparent attenuation of a scattering medium , Bull. seism. Soc. Am. , 73 , 1005 – 1014 . OpenURL Placeholder Text WorldCat Sato H. , 1984 . Attenuation and envelope formation of three-component seismograms of small earthquakes in randomly inhomogeneous lithosphere , J. geophys. Res. , 89 , 1221 – 1241 . Google Scholar Crossref Search ADS WorldCat Spudich P. Ascher U. , 1983 . Calculation of complete theoretical seismograms in vertically varying media using collocation methods , Geophys. J. R. astr. Soc. , 75 , 101 – 124 . Google Scholar Crossref Search ADS WorldCat Takeuchi H. Saito M. , 1972 . Seismic surface waves , in Methods in Computational Physics , vol. 11 , eds Alder B. Fernbach S. Rotenberg M., Academic Press , New York . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Wang C. Y. Herrmann R. B. , 1980 . A numerical study of P-, SV- and SH-wave generation in a plane layered medium , Bull. seism. Soc. Am. , 70 , 1015 – 1036 . OpenURL Placeholder Text WorldCat Wu R. S. Aki K. , 1985 . Elastic wave scattering by a random medium and the small scale inhomogeneities in the lithosphere , J. geophys. Res. , 90 , 10 261 – 10 273 . Google Scholar Crossref Search ADS WorldCat This content is only available as a PDF. Author notes ⋆ Now at: Research School of Earth Sciences, Australian National University, GPO Box 4, Canberra, ACT 26C1, Australia.

Haddon, R. A., W.

doi: 10.1111/j.1365-246X.1987.tb06648.xpmid: N/A

Summary A simple, numerically accurate and efficient method is given for the computation of Green's functions and their spatial derivatives for SH motion in a layered elastic medium. It is shown that with appropriately refined analysis the usual approximate method for the computation of Love waves can be modified to yield the complete solution containing both Love and body waves for SH motion. The complete solution is expressed as a sum of modes of both Love and leaking mode type. Contrary to commonly held notions, no branch line integrals are required. The method applies for both near- and far-field solutions. The application of the method is illustrated with a numerical example. leaking modes, synthetic seismograms, Green's functions References Aki K. Richards P. G. , 1980 . Quantitative Seismology Theory and Methods ( 2 vols ), W. H. Freeman & Co. San Francisco , California . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Alterman Z. S. Karal F. C. , 1968 . Propagation of elastic waves in layered media by finite difference methods , Bull. seism. Soc. Am. , 58 , 367 – 398 . OpenURL Placeholder Text WorldCat Bouchon M. , 1982 . The complete synthesis of seismic crustal phases at regional distances . J. geophys. Res. , 87 , 1735 – 1741 . Google Scholar Crossref Search ADS WorldCat Bouchon M. Aki K. , 1977 . Discrete wavenumber representation of seismic source wavefields , Bull. seism. Soc. Am. , 67 , 259 – 277 . OpenURL Placeholder Text WorldCat Chapman C. H. , 1978 . A new method for computing synthetic seismograms , Geophys. J. R. astr. Soc. , 54 , 481 – 518 . Google Scholar Crossref Search ADS WorldCat Chapman C. H. Drummond R. , 1982 . Body wave seismograms in inhomogeneous media using Maslov asymptotic ray theory , Bull. seism. Soc. Am. , 72 , 8277 – 8317 . OpenURL Placeholder Text WorldCat Cormier V. F. , 1980 . The synthesis of complete seismograms in an earth model specified by radially inhomogeneous layers , Bull. seism. Soc. Am. , 70 , 691 – 716 . OpenURL Placeholder Text WorldCat Fuchs F. Müller G. , 1971 . Computation of synthetic seismograms with the reflectivity method and comparison with observations , Geophys. J. R. astr. Soc. , 23 , 417 – 433 . Google Scholar Crossref Search ADS WorldCat Gilbert F. Helmberger D. V. , 1972 . Generalized ray theory for a layered sphere , Geophys. J. R. astr. Soc. , 27 , 57 – 80 . Google Scholar Crossref Search ADS WorldCat Haddon R. A. W. , 1984 . Computation of synthetic seismograms in layered earth models using leaking modes , Bull. seism. Soc. Am. , 74 , 1225 – 1248 . OpenURL Placeholder Text WorldCat Haddon R. A. W. , 1986 . Exact evaluation of the response of a layered elastic medium to an explosive point source using leaking modes , Bull. seism. Soc. Am. , in press. OpenURL Placeholder Text WorldCat Haddon R. A. W. , 1986 . Response of an Oceanic Waveguide to an Explosive Point Source using leaking modes , in preparation. Harkrider D. G. , 1983 . Synthetics and theoretical seismology , Rev. Geophys. Space Phys. , 21 , 1299 – 1308 . Google Scholar Crossref Search ADS WorldCat Harvey D. J. , 1981 . Seismogram synthesis using normal mode superposition: the locked mode approximation method , Geophys. J. R. astr. Soc. , 66 , 37 – 69 . Google Scholar Crossref Search ADS WorldCat Kamel A. Felsen L. B. , 1981 . Hybrid ray-mode formulation of SH motion in a two-layer half-space . Bull. seism. Soc. Am. , 71 , 1763 – 1781 . OpenURL Placeholder Text WorldCat Kennett B. L. N. , 1980 . Seismic waves in a stratified half-space — II. Theoretical seismograms , Geophys. J. R. astr. Soc. , 61 , 1 – 10 . Google Scholar Crossref Search ADS WorldCat Kind R. , 1978 . The reflectivity method for a buried source , J. Geophys. , 44 , 603 – 612 . OpenURL Placeholder Text WorldCat Richards P. G. , 1971 . Waves in stratified media , Geophysics , 36 , 798 – 809 . Google Scholar Crossref Search ADS WorldCat Rosenbaum J. H. , 1960 . The long time response of a layered elastic medium to explosive sound , J. geophys. Res. , 65 , 1577 – 1613 . Google Scholar Crossref Search ADS WorldCat Smith W. D. , 1975 . The application of finite element analysis to body wave propagation problems . Geophys. J. R. astr. Soc. , 42 , 747 – 768 . Google Scholar Crossref Search ADS WorldCat Wang C. Y. Herrmann R. B. , 1980 . A numerical study of P-, SV-, and SH-wave generation in a plane layered medium , Bull. seism. Soc. Am. , 70 , 1015 – 1036 . OpenURL Placeholder Text WorldCat This content is only available as a PDF.

Norton, Stephen, J.

doi: 10.1111/j.1365-246X.1987.tb06649.xpmid: N/A

Summary Assuming a model of the subsurface characterized by weak fluctuations in both velocity and density, an integral equation is derived for the case of zero-offset reflection data which relates the surface measurements to a scalar reflectivity function given by f(r) = 1 – c20/c(r)2 + 2 ln [ρ(r)/ρ0. In this relation, c(r) and ρ(r) are, respectively, the variable velocity and density of the 3-D medium, and c0 and ρ0 are corresponding reference values. Under the assumptions of the Born approximation, a non-dissipative and non-dispersive medium, and full bandwidth data, the derived integral equation can be solved in closed form for the reflectivity f(r). Using a WKBJ approximation for the Green's function in the depth direction only, a closed-form solution is also derived for f(r) assuming a (known) variable depth-dependent reference velocity. Finally, for the case of a constant background velocity, a band-limited version of f(r) is shown to be recoverable from reflection data limited to a finite (temporal) frequency cutoff. Our ability to reconstruct a reflectivity function containing a variable density term results from the use of zero-offset data, since, under these conditions, the directional dependence of the dipole-like density term in the wave equation is removed, and the density variation manifests itself as a scalar contribution to the reflectivity. inverse scattering, seismic imaging, seismic inversion, seismic migration, variable density References Berkhout A. J. , 1984 . Multidimensional linearized inversion and seismic migration , Geophysics , 49 , 1881 – 1895 . Google Scholar Crossref Search ADS WorldCat Beylkin G. , 1984 . The inversion problem and applications of the generalized Radon transform , Commun. Pure Appl. Math. , 37 , 579 – 599 . Google Scholar Crossref Search ADS WorldCat Beylkin G. , 1985 . Imaging of discontinuities in the inverse scattering problem by inversion of a causal generalized Radon transform , J. math. Phys. , 26 , 99 – 108 . Google Scholar Crossref Search ADS WorldCat Bleistein N. , 1984 . Mathematical Methods of Wave Phenomena , Academic , New York . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Bleistein N. Cohen J. K. Hagin F. G. , 1985 . Computational and asymptotic aspects of velocity inversion , Geophysics , 50 , 1243 – 1265 . Google Scholar Crossref Search ADS WorldCat Cheng G. Coen S. , 1984 . The relationship between Born inversion and migration for common-midpoint stacked data , Geophysics , 49 , 2117 – 2131 . Google Scholar Crossref Search ADS WorldCat Chernov L. A. , . Wave Propagation in a Random Medium , Dover , New York . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Clayton R. W. Stolt R. H. , 1981 . A Born-WKBJ inversion method for acoustic reflection data , Geophysics , 46 , 1559 – 1567 . Google Scholar Crossref Search ADS WorldCat Cohen J. K. Bleistein N. , 1979 . Velocity inversion procedure for acoustic waves , Geophysics , 44 , 1077 – 1087 . Google Scholar Crossref Search ADS WorldCat Cohen J. K. Hagin F. G. , 1985 . Velocity inversion using a stratified reference , Geophysics , 50 , 1689 – 1700 . Google Scholar Crossref Search ADS WorldCat Gray S. H. Bleistein N. , 1986 . Imaging and inversion of zero-offset seismic data , Proc. IEEE , 74 , 440 – 456 (special issue on seismic inversion). Google Scholar Crossref Search ADS WorldCat Hooshyar M. A. Weglein A. B. , 1986 . Inversion of the two-dimensional SH elastic wave equation for the density and shear modulus , J. acoust. Soc. Am. , 79 , 1280 – 1283 . Google Scholar Crossref Search ADS WorldCat Norton S. J. Linzer M. , 1981 . Ultrasonic reflectivity imaging in three dimensions: exact solutions for plane, cylindrical and spherical apertures , IEEE Trans. Biom. Eng. , BME-28 , 202 – 220 (special issue on image reconstruction). Google Scholar Crossref Search ADS WorldCat Norton S. J. , 1983 . Generation of separate density and compressibility images in tissue , Ultrasonic Imaging , 5 , 240 – 252 . Google Scholar Crossref Search ADS PubMed WorldCat Raz S. , 1981 . Three-dimensional velocity profile inversion for finite-offset data , Geophysics , 46 , 837 – 842 . Google Scholar Crossref Search ADS WorldCat Raz S. , 1982 . A procedure for multi-dimensional inversion of seismic data , Geophysics , 47 , 1422 – 1430 . Google Scholar Crossref Search ADS WorldCat Stolt R. H. Weglein A. B. , 1985 . Migration and inversion of seismic data , Geophysics , 50 , 2458 – 2472 . Google Scholar Crossref Search ADS WorldCat Wolf E. , 1969 . Three-dimensional structure determination of semi-transparent objects from holographic data , Optics Commun. , 1 , 153 – 156 . Google Scholar Crossref Search ADS WorldCat This content is only available as a PDF.

Sayers, C., M.

doi: 10.1111/j.1365-246X.1987.tb06650.xpmid: N/A

Summary Seismic anisotropy observed in the upper mantle is primarily due to the partial alignment of crystallites of olivine and pyroxene, which have orthorhombic crystallographic symmetry. In this paper, the crystallite orientation distribution function is used to derive expressions for the anisotropy of elastic wave velocities in a partially aligned aggregate of orthorhombic crystallites. The coefficients Wlmn of a series expansion of the crystallite orientation distribution function in generalized spherical harmonics can be obtained to order l = 2 from the angular variation of the elastic wave velocities. This corresponds to the specification of the distribution function by its first few moments. seismic anisotropy, elastic waves, effective moduli, upper mantle, olivine References Ando M. Ishikawa Y. , 1932 . Observation of shear-wave velocity polarization anisotropy beneath Honshu, Japan , J. Phys. , 30 , 191 – 199 . OpenURL Placeholder Text WorldCat Ando M. Ishikawa Y. Wada H. , 1980 . S-wave anisotropy in the upper mantle under a volcanic area in Japan , Nature , 286 , 43 – 46 . Google Scholar Crossref Search ADS WorldCat Christensen N. I. , 1984 . The magnitude, symmetry and origin of upper mantle anisotropy based on fabric analyses of ultramafic tectonites , Geophys. J. R. astr. Soc. , 76 , 89 – 111 . Google Scholar Crossref Search ADS WorldCat Crampin S. Bamford D. , . Inversion of P-wave velocity anisotropy , Geophys. J. R. astr. Soc. , 49 , 123 – 132 . Google Scholar Crossref Search ADS WorldCat Fitch J. P. , 1985 . Solving algebraic problems with REDUCE , J. Symbol. Comput. , 1 , 211 – 227 . Google Scholar Crossref Search ADS WorldCat Forsyth D. W. , 1975 . The early structural evolution and anisotropy of the oceanic upper mantle , Geophys. J. R. astr. Soc. , 43 , 103 – 162 . Google Scholar Crossref Search ADS WorldCat Francis T. J. G. , 1969 . Generation of seismic anisotropy in the upper mantle along the mid-oceanic ridges , Nature , 221 , 162 – 165 . Google Scholar Crossref Search ADS WorldCat Hess H. , 1964 . Seismic anisotropy of the uppermost mantle under oceans , Nature , 203 , 629 – 631 . Google Scholar Crossref Search ADS WorldCat Kumazawa M. , 1969 . The elastic contants of single crystal orthopyroxene , J. geophys. Res. , 74 , 5973 – 5980 . Google Scholar Crossref Search ADS WorldCat Kumazawa M. Anderson O. L. , 1969 . Elastic moduli, pressure derivatives and temperature derivatives of single crystal olivine and single crystal forsterite , J. geophys. Res. , 74 , 5961 – 5972 . Google Scholar Crossref Search ADS WorldCat Morris P. R. , 1969 . Averaging fourth-rank tensors with weight functions , J. appl. Phys. , 40 , 447 – 448 . Google Scholar Crossref Search ADS WorldCat Musgrave M. J. P. , 1970 . Crystal Acoustics , Holden-Day , San Francisco . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Raitt R. W. Shor G. G. Morris G. B. Kirk H. K. , 1971 . Mantle anisotropy in the Pacific Ocean , Tectonophys. , 12 , 173 – 186 . Google Scholar Crossref Search ADS WorldCat Roe R. J. , 1965 . Description of crystallite orientation in polycrystalline materials — III: General solution to pole figure inversion , J. appl. Phys. , 36 , 2024 – 2031 . Google Scholar Crossref Search ADS WorldCat Roe R. J. , 1966 . Inversion of pole figures for materials having cubic crystal symmetry , J. appl. Phys. , 37 , 2069 – 2072 . Google Scholar Crossref Search ADS WorldCat Roe R. J. Krigbaum W. R. , 1964 . Description of crystallite orientation in polycrystalline materials having fibre texture , J. Chem. Phys. , 40 , 2608 – 2615 . Google Scholar Crossref Search ADS WorldCat This content is only available as a PDF. Author notes ⋆ Present address: General Research and Mathematics, Koninklijke/Shell Exploratie en Produktie Laboratorium, Volmerlaan 6, 2288 GD Rijswijk ZH, The Netherlands.

Warner, M., R.

doi: 10.1111/j.1365-246X.1987.tb06651.xpmid: N/A

Summary Deep seismic reflection profiling has become an established technique for studying the continental lithosphere. The base of the crust can be identified on many deep profiles and it correlates closely with the Moho determined by refraction studies. On many reflection profiles the Moho appears at a rather constant two-way travel time despite the highly variable structure of the crust above. It is shown that the apparent flatness of the Moho on reflection time sections is an artefact produced when the crust is in local isostatic equilibrium. The true geometry of the Moho can only be determined if accurate and spatially well-resolved seismic velocities are obtained from the lower crust. The degree of isostatic compensation can be assessed from deep reflection data and an equivalent elastic thickness calculated. The elastic thickness around the UK is very small, only 2–3 km. It is suggested that the many major fault zones visible on the seismic data weaken the lithosphere to produce these low values. Moho, isostasy, deep seismic reflection, seismic velocities, elastic thickness, lower crust References Barton P. Matthews D. H. Hall J. Warner M. R. , 1984 . Moho beneath the North Sea compared on normal incidence and wide-angle seismic records , Nature , 308 , 55 – 56 . Google Scholar Crossref Search ADS WorldCat Barton P. Wood R. , 1984 . Tectonic evolution of the North Sea basin: crustal stretching and subsidence , Geophys. J. R. astr. Soc. , 79 , 987 – 1922 . Google Scholar Crossref Search ADS WorldCat Bodine J. H. Steckler M. R. Watts A. B. , 1981 . Observations of flexure and the rheology of the oceanic lithosphere , J. geophys. Res. , 86 , 3695 – 3707 . Google Scholar Crossref Search ADS WorldCat Brewer J. A. Matthews D. H. Warner M. R. Hall J. Smythe D. K. Whittington R. J. , 1983 . BIRPS deep seismic reflection studies of the British Caledonides , Nature , 305 , 206 – 210 . Google Scholar Crossref Search ADS WorldCat Buhl P. Diebold J. B. Stoffa P. L. , 1982 . Array length magnification through the use of multiple sources and receiving arrays , Geophysics , 47 , 311 . Google Scholar Crossref Search ADS WorldCat Cheadle M. J. McGeary S. Warner M. R. Matthews D. H. , 1987 . Extensional structures on the western UK continental shelf: a review of evidence from deep seismic profiling , in Continental Extensional Tectonics , ed. Coward M. P. Dewey J. F. Hancock P. L., pp. 445 – 465 , Geol. Soc. Special Publication, Blackwell Scientific Publication , Oxford . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Hall J. Simmons G. , 1979 . Seismic velocities of Lewisian metamorphic rocks at pressures to 8kbar: relationship to crustal layering in north Britain , Geophys. J. R. astr. Soc. , 58 , 337 – 347 . Google Scholar Crossref Search ADS WorldCat Kusznir N. Karner G. , 1985 . Dependence of the flexural rigidity of the continental lithosphere on rheology and temperature , Nature , 316 , 138 – 142 . Google Scholar Crossref Search ADS WorldCat Ludwig W. J. Nafe J. E. Drake C. L. , 1970 . Seismic refraction , in The Sea , ed. Maxwell A. E., 4 ( 1 ), pp. 53 – 84 , Wiley Interscience , New York . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC McGeary S. Warner M. R. , 1985 . Seismic profiling the continental lithosphere , Nature , 317 , 795 – 797 . Google Scholar Crossref Search ADS WorldCat Matthews D. H. Cheadle M. J. , 1985 . Deep reflections from the Caledonides and Variscides west of Britain and comparison with the Himalayas , in Reflection Seismology: A Global Perspective , ed. Barazangi M., Am. Geophys. Un. Geodynam. Ser. , 13 , 5 – 19 . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Mutter J. C. , 1985 . Multichannel seismic images of the oceanic crust's internal structure , Geology , 13 , 629 – 633 . Google Scholar Crossref Search ADS WorldCat Turcotte D. L. Schubert G. , 1982 . Geodynamics Applications of Continuum Physics to Geological Problems , John Wiley & Sons , New York . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Warner M. R. , 1985 . Deep seismic reflection profiling of the continental crust at sea , in Reflection Seismology: A Global Perspective , ed. Barazangi M., Am. Geophys. Un. Geodynam. Ser. , 13 , 629 – 633 . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC This content is only available as a PDF.

Hinnov, Linda, A.;Wilson, Clark, R.

doi: 10.1111/j.1365-246X.1987.tb06652.xpmid: N/A

Summary The major source of the excitation of the Chandler wobble has not yet been established but is believed to be primarily meteorological in origin. Previous studies of the meteorological excitation of the Chandler wobble have measured only effects from motions in the atmosphere and the oceans. The role of global water storage has been regarded as unimportant because of its relatively minor role in the excitation of the annual wobble. In addition, an appropriate hydrological dataset has not been readily available for global measurements of an extended monthly time series of the water storage contribution to the Chandler wobble's excitation. Thus, an evaluation of the contribution has never been attempted. However, a crude estimate of the global water storage series is possible using worldwide records of monthly precipitation and temperature, accumulating precipitation at individual locations whenever temperatures are at 0°C or below. Comparison of this modelled series with a previous estimate of the annual component of the global water balance, and with the observed monthly polar motion series, indicates good agreement with the former, and a significant correlation with the latter near the Chandler frequency. Combining the estimated water storage series with a previously computed atmospheric excitation series produces better Chandler frequency coherence with the ILS polar motion data than is obtained with either series separately. polar motion, wobble, global water storage References Barnes R. T. H. Hide R. White A. A. Wilson C. A. , 1983 . Atmospheric angular momentum fluctuations, length-of-day changes and polar motion , Proc. R. Soc. Lond. A , 387 , 31 – 73 . Google Scholar Crossref Search ADS WorldCat Chandler S. C. , 1891 . On the variation of latitude - II , Astr. J. 11 , 65 – 70 . Google Scholar Crossref Search ADS WorldCat Chandler S. C. , 1894 . On some further characteristics of the polar rotation , Astr. J. , 14 , 82 – 84 . Google Scholar Crossref Search ADS WorldCat Hassan E. S. M. , 1960 . Fluctuations in the atmospheric inertia: 1873–1950 , Meteorol. Monogr. , 4 , 1 – 40 . OpenURL Placeholder Text WorldCat Jeffreys H. , 1916 . Causes contributory to the annual variation in latitude , Mon. Not. R. astr. Soc. , 76 , 499 – 525 . Google Scholar Crossref Search ADS WorldCat Koopmans L. H. , 1974 . The Spectral Analysis of Time Series , Academic Press , New York . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Kotlyakov V. M. , 1967 . General features of snow and associated phenomena in the world , in Physics of Snow, Avalanches, and Glaciers , eds Sulakvelidze Dolov, Indian National Scientific Documentation Centre , New Delhi . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Lambeck K. , 1980 . The Earth's Variable Rotation: Geophysical Causes and Consequences , Cambridge University Press . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Munk W. H. Hassan E. S. M. , 1961 . Atmospheric excitation of the Earth's wobble , Geophys. J. R. astr. Soc. , 4 , 339 – 358 . Google Scholar Crossref Search ADS WorldCat Munk W. H. MacDonald G. J. F. , 1975 . The Rotation of the Earth , Cambridge University Press . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Newcomb S. , 1891 . On the periodic variation of latitude, and the observations with the Washington prime-vertical transit , Astr. J. N. Y. , 11 , 81 – 82 . Google Scholar Crossref Search ADS WorldCat Smith M. L. Dahlen F. A. , 1981 . The period and Q of the Chandler wobble , Geophys. J. R. astr. Soc. , 64 , 223 – 281 . Google Scholar Crossref Search ADS WorldCat Spangler W. M. L. Jenne R. L. , 1984 . World Monthly Surface Station Climatology , National Center for Atmospheric Research , Colorado . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC UNESCO , 1978 . World Water Balance and Water Resources of the Earth , UNESCO Press , Leningrad . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Google Scholar von Hylckama T. E. A. , 1970 . Water balance and Earth unbalance , Proc. Read. Symp. World Water Balance , 92 , 434 – 553 . OpenURL Placeholder Text WorldCat Wahr J. M. , 1982 . Effects of the atmosphere and oceans on the Earth's wobble - I. Theory , Geophys. J. R. astr. Soc. , 70 , 349 – 372 . Google Scholar Crossref Search ADS WorldCat Wahr J. M. , 1983 . Effects of the atmosphere and oceans on the Earth's wobble - II. Results , Geophys. J. R. astr. Soc. , 74 , 451 – 487 . OpenURL Placeholder Text WorldCat Wilson C. R. Haubrich R. A. , 1976 . Meteorological excitation of the Earth's wobble , Geophys. J. R. astr. Soc. , 46 , 707 – 743 . Google Scholar Crossref Search ADS WorldCat Wilson C. R. Haubrich R. A. , 1976 . Atmospheric contributions to the excitation of the Earth's wobble 1901–1970 , Geophys. J. R. astr. Soc. , 46 , 745 – 760 . Google Scholar Crossref Search ADS WorldCat Wilson C. R. Vicente R. O. , 1980 . An analysis of the homogeneous ILS polar motion series , Geophys. J. R. astr. Soc. , 62 , 605 – 616 . Google Scholar Crossref Search ADS WorldCat Wilson C. R. , 1985 . Discrete polar motion equations , Geophys. J. R. astr. Soc. , 80 , 551 – 554 . Google Scholar Crossref Search ADS WorldCat Yumi S. Yokoyama K. , 1980 . Results of the ILS in a Homogeneous System 1899.9–1979.0 , Central Bureau of the International Polar Motion Service, International Latitude Observatory of Mizusawa , Japan . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC This content is only available as a PDF. Author notes ⋆ Now at the Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, Maryland 21218, USA.

Stening, R., J.;Winch, D., E.

doi: 10.1111/j.1365-246X.1987.tb06653.xpmid: N/A

Summary Hourly values from 1964–65 of the three geomagnetic elements from a large number of stations have been analysed for the various lunar components. These were combined to examine in detail the seasonal and diurnal variations of the lunar geomagnetic tide at night. Comparison of the values for the oceanic component calculated in a similar way to Malin (1973) showed good agreement between sunspot maximum and minimum years. When seasonal changes were included, the D and Z elements gave evidence of a lunar modulation of magnetic field aligned currents entering the ionosphere in auroral regions. The effects of these currents appeared to extend as far away as the equator. Changes in their amplitude during the night also suggest a relation to auroral processes. There is a just-resolved nighttime equatorial electrojet H component and a quite large lunar H component in the auroral regions. lunar, electric currents, geomagnetic, auroral References Gupta J. C. , 1967 . Lunar variations in the auroral zone , Nature , 215 , 607 . Google Scholar Crossref Search ADS WorldCat Gupta J. C. , 1974 . Lunar ionospheric and oceanic dynamo variations , Gerlands Beitr. Geophys. , 83 , 1 – 15 . OpenURL Placeholder Text WorldCat Hartz T. R. Brice N. M. , 1967 . The general pattern of auroral particle precipitation , Planet. Space Sci. , 15 , 301 – 329 . Google Scholar Crossref Search ADS WorldCat Iijima T. Potemra T. A. , 1978 . Large-scale characteristics of field-aligned currents associated with substorms , J. geophys. Res. , 83 , 599 . Google Scholar Crossref Search ADS WorldCat Lisitzin E. , 1974 . Sea Level Changes , Elsevier , Amsterdam . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Malin S. R. C. , 1970 . Separation of lunar daily geomagnetic variations into parts of ionospheric and oceanic origin , Geophys. J. R. astr. Soc. , 21 , 447 – 455 . Google Scholar Crossref Search ADS WorldCat Malin S. R. C. , 1973 . Worldwide distribution of geomagnetic tides , Phil. Trans. R. Soc. A , 274 , 551 – 594 . Google Scholar Crossref Search ADS WorldCat Matsushita S. Campbell W. H. , 1972 . Lunar semidiurnal variations of the geomagnetic field determined from 2.5 min data scalings , J. atmos. terr. Phys. , 34 , 1187 – 1200 . Google Scholar Crossref Search ADS WorldCat Matsushita S. Xu W.-Y. , 1983 . Equivalent ionospheric current systems representing lunar daily variations of the polar geomagnetic field , J. geophys. Res. , 88 , 7143 – 7154 . Google Scholar Crossref Search ADS WorldCat Parkinson W. D. Jones F. W. , 1979 . The geomagnetic coast effect , Rev. Geophys. Space Phys. , 17 , 1999 – 2015 . Google Scholar Crossref Search ADS WorldCat Sastri N. S. Rao D. R. K. , 1971 . Separation of lunar daily geomagnetic variations into parts of oceanic and ionospheric origin in the Indian region , Geophys. J. R. astr. Soc. , 23 , 269 – 272 . Google Scholar Crossref Search ADS WorldCat Schlapp D. M. , 1977 . Lunar geomagnetic tides and the ocean dynamo , J. atmos. terr Phys. , 39 , 1453 – 1457 . Google Scholar Crossref Search ADS WorldCat Schlapp D. M. , 1978 . Lunar daily geomagnetic variations at Tucson , Geophys. J. R. astr. Soc. , 55 , 183 – 191 . Google Scholar Crossref Search ADS WorldCat Schlapp D. M. Malin S. R. C. , 1979 . Some features of the seasonal variation of geomagnetic lunar tides , Geophys. J. R. astr. Soc. , 59 , 161 – 170 . Google Scholar Crossref Search ADS WorldCat Schuster A. , 1908 . The diurnal variation of terrestrial magnetism . Phil. Trans. R. Soc. A , 208 , 163 – 204 . Google Scholar Crossref Search ADS WorldCat Sellek R. Schlapp D. M. , 1984 . Nighttime lunar geomagnetic tides at stations far from the ocean , Geophys. J. R. astr. Soc. , 76 , 581 – 585 . Google Scholar Crossref Search ADS WorldCat Stening R. J. , 1986 . Lunar effects in the F region of the ionosphere , J. geophys. Res. , 91 , 4581 – 4584 . Google Scholar Crossref Search ADS WorldCat Stening R. J. Winch D. E. , 1979 . Seasonal changes in the global lunar geomagnetic variation , J. atmos. terr. Phys. , 41 , 311 – 323 . Google Scholar Crossref Search ADS WorldCat Stening R. J. Winch D. E. , 1987 . Nighttime geomagnetic variations at low latitudes , Planet. Space Sci. . OpenURL Placeholder Text WorldCat Winch D. E. , 1981 . Spherical harmonic analysis of geomagnetic tides 1964–65 . Phil. Trans. R. Soc. A , 303 , 1 – 104 . Google Scholar Crossref Search ADS WorldCat Winch D. E. Cunningham R. A. , 1972 . Lunar magnetic tides at Watheroo: seasonal, elliptic, evectional, variational and nodal components . J. geomagn. Geolectr. , 24 , 381 – 414 . Google Scholar Crossref Search ADS WorldCat This content is only available as a PDF.

Ingham, M., R.;Gough, D., I.;Parkinson, W., D.

doi: 10.1111/j.1365-246X.1987.tb06654.xpmid: N/A

Summary Extensive 2-D forward modelling has been used to study conductive structures beneath the Cordillera, the Rocky Mountains and the Rocky Mountain Trench of western Canada. Both large-scale geology and magnetovariation anomalies indicate generally 2-D structure. Eleven stations close to a profile transverse to strike were chosen from two magnetovariation arrays. The response parameter modelled at these stations is the real part of Z/H for a linearly polarized uniform horizontal primary field, along the profile and transverse to the structures, calculated from single-station transfer functions at periods of 600 and 1500 s. Induction arrows indicate that the quadrature phase response is related mainly to currents induced in sedimentary rocks in another conductor. Very large real Z/H, at stations in the Main Ranges, and small values 50 km SW of these, in the Rocky Mountain Trench, can be modelled by currents induced in highly conductive rocks, rising to within a few kilometres of the surface, beneath the Main Ranges. This conductive ridge is well constrained in position and depth. It is joined to the Canadian Cordilleran Regional conductive layer, and is essentially a thickening of the CCR conductor along its edge. The best purely inductive model places the top of the CCR conductor within 5 km of the surface, but it can be modelled at greater depth if the entire conductive structure carries a small amount of channelled current in addition to the induced currents. Available magnetotelluric soundings indicate a midcrustal depth to the CCR conductor SW of Revelstoke, but depths of 5 km or less under the Rocky Mountains and Trench, in good agreement with our models fitted to long-period magnetovariation fields. The nature of the CCR conductor has been considered elsewhere: its high conductivity may be due to silicate partial melt in interconnected pores at upper mantle depths, with saline hot water in interconnected pores and fractures at crustal depths. electromagnetic induction, conductive structure, Canadian Cordillera References Bailey R. C. Edwards R. N. Garland G. D. Kurtz R. D. Pitcher D. , 1974 . Electrical conductivity studies over a tectonically active area in eastern Canada , J. Geomagn. Geoelect. , 26 , 125 – 146 . Google Scholar Crossref Search ADS WorldCat Bingham D. K. Gough D. I. Ingham M. R. , 1985 . Conductive structures under the Canadian Rocky Mountains , Can. J. Earth Sci. , 22 , 384 – 398 . OpenURL Placeholder Text WorldCat Brewitt-Taylor C. R. Weaver J. H. , 1976 . On the finite difference solution of two-dimensional induction problems , Geophys. J. R. astr. Soc. , 47 , 375 – 396 . Google Scholar Crossref Search ADS WorldCat Camfield P. A. Gough D. I. Porath H. , 1971 . Magnetometer array studies in the northwestern United States and southwestern Canada , Geophys. J. R. astr. Soc. , 22 , 201 – 221 . Google Scholar Crossref Search ADS WorldCat Caner B. , 1971 . Quantitative interpretation of geomagnetic depth-sounding data in western Canada , J. geophys. Res. , 76 , 7202 – 7216 . Google Scholar Crossref Search ADS WorldCat Caner B. Auld D. R. Dragert H. Camfield P. A. , 1971 . Geomagnetic depth-sounding and crustal structure in western Canada , J. geophys. Res. , 76 , 7181 – 7201 . Google Scholar Crossref Search ADS WorldCat Caner B. Camfield P. A. Andersen F. Niblett E. R. , 1969 . A large-scale magnetotelluric survey in western Canada , Can. J. Earth Sci. , 6 , 1245 – 1261 . Google Scholar Crossref Search ADS WorldCat Caner B. Cannon W. H. Livingstone C. E. , 1967 . Geomagnetic depth sounding and upper mantle structure in the cordillera regions of western North America , J. geophys. Res. , 72 , 6335 – 6351 . Google Scholar Crossref Search ADS WorldCat Cochrane N. A. Hyndman R. D. , 1970 . A new analysis of geomagnetic depth-sounding data from western Canada , Can. J. Earth Sci. , 7 , 1208 – 1218 . Google Scholar Crossref Search ADS WorldCat Dragert H. , 1973 . A transfer function analysis of a geomagnetic depth sounding profile across central British Columbia , Can. J. Earth Sci. , 10 , 1089 – 1098 . Google Scholar Crossref Search ADS WorldCat Dragert H. Clarke G. K. C. , 1977 . A detailed investigation of the Canadian cordillera geomagnetic transition anomaly , J. Geophys. , 42 , 373 – 390 . OpenURL Placeholder Text WorldCat Dragert H. Law L. K. Sule P. O. , 1980 . Magnetotelluric soundings across the Pemberton Volcanic Belt, British Columbia , Can. J. Earth Sci. , 17 , 161 – 167 . Google Scholar Crossref Search ADS WorldCat Flores C. Kurtz R. D. Laurier J. , 1985 . Magnetotelluric exploration in the Meager Mountain geothermal area, Canada , Acta Geodaet. Geophys. Montanist. , 20 , 165 – 171 . OpenURL Placeholder Text WorldCat Gough D. I. , 1986 . Mantle upflow tectonics in the Canadian Cordillera , J. geophys. Res. , 91 , 1909 – 1919 . Google Scholar Crossref Search ADS WorldCat Gough D. I. Bingham D. K. Ingham M. R. Alabi A. O. , 1982 . Conductive structure in southwestern Canada: a regional magnetometer array study , Can. J. Earth Sci. , 19 , 1630 – 1690 . Google Scholar Crossref Search ADS WorldCat Hutton V. R. S. Gough D. I. Dawes G. K. C. Travassos J. , 1987 . Magnetotelluric soundings in the Canadian Rocky Mountains , Geophys. J. R. astr. Soc. , in press. OpenURL Placeholder Text WorldCat Hyndman R. D. , 1963 . Electrical conductivity inhomogeneities in the Earth's upper mantle , MSc thesis , University of British Columbia , Vancouver . Kurtz R. D. Laurier J. M. Gupta J. C. , 1986 . A magnetotelluric sounding across Vancouver Island sees the subducting Juan de Fuca Plate , Nature , 321 , 596 – 599 . Google Scholar Crossref Search ADS WorldCat Porath H. Dziewonski A. M. , 1971 . Crustal electrical and conductivity anomalies in the Great Plains Province of the United States , Geophysics , 36 , 382 – 395 . Google Scholar Crossref Search ADS WorldCat This content is only available as a PDF.

Bhuyan, P., K.;Tyagi, T., R.

doi: 10.1111/j.1365-246X.1987.tb06655.xpmid: N/A

Summary Equivalent slab thickness data obtained at Delhi during the ascending half of this solar cycle from 1978 to 1980 have been analysed by the Chapman—Miller method to compute the lunar and solar daily variations. Significant diurnal and seasonal variations were observed for the lunar as well as the solar terms. There is no apparent correlation between these variations and sunspot activity. The occurrence of the most significant lunar term, the lunar semidiurnal component, coincides with the diffusion caused by the additional fountain effect generated by the lunar semidiurnal variation of the electric field at the equatorial region. Except for the phase, the results obtained for slab thickness differ from those reported for ionospheric electron content for the same period and location. electron content, slab thickness, lunar and solar daily variation References Bernhardt P. A. Antoniadis D. A. da Rosa A. V. , 1976 . Lunar perturbations in columnar electron content and their interpretation in terms of dynamo electric fields , J. geophys. Res. , 81 , 5957 . Google Scholar Crossref Search ADS WorldCat Bhuyan P. K. Tyagi T. R. , 1986 . Lunar and solar daily variations of ionospheric electron content at Delhi , J. atmos. terr. Phys. , 48 , 301 – 310 . Google Scholar Crossref Search ADS WorldCat Chandra H. Sethia G. Rastogi R. G. , 1981 . Lunar oscillations in TEC around the anomaly peak region in India , J. atmos. terr. Phys. , 43 , 845 – 849 . Google Scholar Crossref Search ADS WorldCat Chapman S. Miller J. C. P. , 1940 . The statistical determination of lunar daily variations in geomagnetic and meteorological element , Mon. Not. R. astr. Soc. Geophys. Suppl. , 4 , 649 – 669 . Google Scholar Crossref Search ADS WorldCat Huang Y. N. , 1979 . Solar cycle and seasonal variations of the solar and lunar daily variations of total electron content at Lunping , J. geophys. Res. , 84 , 6595 – 6601 . Google Scholar Crossref Search ADS WorldCat Huang Y. N. , 1983 . Some results of ionospheric slab thickness observations at Lunping , J. geophys. Res. , 88 , 5517 – 5522 . Google Scholar Crossref Search ADS WorldCat Leaton B. R. Malin S. R. C. Finch H. F. , 1962 . The solar and lunisolar daily variations of the geomagnetic field at Greenwich and Abinger, 1916–1957 , R. Greenwich Obs. Bull. , 63 , D273 . OpenURL Placeholder Text WorldCat Malin S. R. C. Chapman S. , 1970 . The determination of lunar daily geophysical variations by Chapman-Miller method , Geophys. J. R. astr. Soc. , 19 , 15 – 35 . Google Scholar Crossref Search ADS WorldCat Martyn D. F. , 1947 . Atmospheric tides in the ionosphere, 2 , Proc. R. Soc. Lond. ser. A , 190 , 273 . Google Scholar Crossref Search ADS WorldCat Matsushita S. , 1967 . Lunar tides in the ionosphere , in Encyclopaedia of Physics , 49/111/2 , Springer , New York . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Rao N. N. Stubenrauch C. F. , 1967 . Lunar tidal variation in the equivalent slab thickness of the ionosphere over Hawaii , J. geophys. Res. , 72 , 5547 . Google Scholar Crossref Search ADS WorldCat Trivedi Rastogi , 1969 . Lunar tidal oscillations in horizontal magnetic intensity at Kodaikanal during periods of low and high sunshots , Indian J. Met. Geophys. , 20 , 235 . OpenURL Placeholder Text WorldCat This content is only available as a PDF.