Global mantle shear velocity model developed using nonlinear asymptotic coupling theory

We present a three-dimensional shear velocity model of the whole mantle developed using S H waveform data. The model is expressed horizontally in terms of spherical harmonics up to degree 12, and vertically in terms of Legendre polynomials up to degrees 5 and 7 in the upper and lower mantle, respectively. What distinguishes this model from other tomographic models published to date is (1) the theoretical normal mode-based wave propagation approach, where we include across branch mode coupling terms in order to model the body wave sensitivity to structure along the path more accurately; (2) the wave-packet weighting scheme which allows to balance contributions from high-amplitude and low-amplitude phases, increasing the resolution in some parts of the mantle. We also relax the constraints on the Moho depth, which is allowed to vary in the inversion, thus absorbing some uncertainties in crustal structure. The resulting model is generally in good agreement with other recent global mantle S velocity models and with some regional models. The rms profile with depth has more power than other models in the upper mantle/lower mantle transition region and the zone of increased power and low degree structure near the base of the mantle is confined to the last 500 km in depth. This model provides a particularly good fit to the non-hydrostatic geoid through harmonic degree 12 (79% variance reduction), as well as good fits to observed splitting functions of S velocity sensitive mantle modes, indicating that both large-scale and small-scale features are really well constrained.

[1]  C. Vigny,et al.  Mantle dynamics with induced plate tectonics , 1989 .

[2]  Bradford H. Hager,et al.  Large‐scale heterogeneities in the lower mantle , 1977 .

[3]  John H. Woodhouse,et al.  Mapping the upper mantle: Three‐dimensional modeling of earth structure by inversion of seismic waveforms , 1984 .

[4]  R. Hilst,et al.  Effects of relative plate motion on the deep structure and penetration depth of slabs below the Izu-Bonin and Mariana island arcs , 1993 .

[5]  B. Hager,et al.  Geoid Anomalies in a Dynamic Earth , 1984 .

[6]  E. Mochizuki.  Free oscillations and surface waves of an aspherical Earth , 1986 .

[7]  P. Shearer,et al.  Global mapping of topography on the 660-km discontinuity , 1992, Nature.

[8]  S. Grand.  Mantle shear structure beneath the Americas and surrounding oceans , 1994 .

[9]  Thomas H. Jordan,et al.  Composition and development of the continental tectosphere , 1978, Nature.

[10]  J. Woodhouse.  The coupling and attenuation of nearly resonant multiplets in the Earth's free oscillation spectrum , 1980 .

[11]  Robert L. Woodward,et al.  Global upper mantle structure from long-period differential travel times , 1991 .

[12]  B. Romanowicz.  A global tomographic model of shear attenuation in the upper mantle , 1995 .

[13]  T. Tanimoto,et al.  Global anisotropy in the upper mantle inferred from the regionalization of phase velocities , 1990 .

[14]  David J. Stevenson,et al.  Effects of an endothermic phase transition at 670 km depth in a spherical model of convection in the Earth's mantle , 1993, Nature.

[15]  J. Woodhouse,et al.  Constraining Upper Mantle Anelasticity Using Surface Wave Amplitude Anomalies , 1993 .

[16]  A. Dziewoński,et al.  Acoustic imaging at the planetary scale , 1992 .

[17]  W. Peltier,et al.  Lateral heterogeneity in the convecting mantle , 1986 .

[18]  B. Romanowicz,et al.  Modelling of coupled normal modes of the Earth: the spectral method , 1990 .

[19]  Wei-jia Su,et al.  Degree 12 model of shear velocity heterogeneity in the mantle , 1994 .

[20]  Wei-jia Su,et al.  Predominance of long-wavelength heterogeneity in the mantle , 1991, Nature.

[21]  M. Richards,et al.  A geodynamic model of mantle density heterogeneity , 1993 .

[22]  D. Jackson.  The use of a priori data to resolve non‐uniqueness in linear inversion , 1979 .

[23]  Barbara Romanowicz.  Seismic Tomography of the Earth's Mantle , 1991 .

[24]  T. Tanimoto,et al.  Global Love wave phase velocity variation and its significance to plate tectonics , 1991 .

[25]  F. A. Dahlen,et al.  The Effect of A General Aspherical Perturbation on the Free Oscillations of the Earth , 1978 .

[26]  F. Dahlen.  The Normal Modes of a Rotating, Elliptical Earth , 1968 .

[27]  Tatsuhiko Hara,et al.  Two efficient algorithms for iterative linearized inversion of seismic waveform data , 1993 .

[28]  T. Jordan.  The continental tectosphere , 1975 .

[29]  B. Romanowicz.  The upper mantle degree 2: Constraints and inferences from global mantle wave attenuation measurements , 1990 .

[30]  NADW formation as a branch of the hydrological cycle , 1992 .

[31]  D. L. Anderson,et al.  Measurements of mantle wave velocities and inversion for lateral heterogeneities and anisotropy: 3. Inversion , 1986 .

[32]  John H. Woodhouse,et al.  Determination of earthquake source parameters from waveform data for studies of global and regional seismicity , 1981 .

[33]  Wei-jia Su,et al.  On the scale of mantle heterogeneity , 1992 .

[34]  Jeannot Trampert,et al.  Global phase velocity maps of Love and Rayleigh waves between 40 and 150 seconds , 1995 .

[35]  B. Hager,et al.  Long-wavelength variations in Earth’s geoid: physical models and dynamical implications , 1989, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[36]  W. G. Hoover.  molecular dynamics , 1986, Catalysis from A to Z.

[37]  A. Dziewoński,et al.  Seismic Surface Waves and Free Oscillations in a Regionalized Earth Model , 1982 .

[38]  Mark A. Richards,et al.  Effect of depth-dependent viscosity on the planform of mantle convection , 1996, Nature.

[39]  Robert A. Phinney,et al.  Representation of the Elastic ‐ Gravitational Excitation of a Spherical Earth Model by Generalized Spherical Harmonics , 1973 .

[40]  B. Romanowicz,et al.  Degrees 2, 4, 6 inferred from seismic tomography , 1993 .

[41]  Adam M. Dziewonski,et al.  Mapping the lower mantle: Determination of lateral heterogeneity in P velocity up to degree and order 6 , 1984 .

[42]  Robert W. Clayton,et al.  Lower mantle heterogeneity, dynamic topography and the geoid , 1985, Nature.

[43]  G. Masters,et al.  Observations of anomalous splitting and their interpretation in terms of aspherical structure , 1986 .

[44]  R. V. D. Hilst.  Complex morphology of subducted lithosphere in the mantle beneath the Tonga trench , 1995, Nature.

[45]  G. Masters,et al.  Lower-mantle structure from ScS–S differential travel times , 1991, Nature.

[46]  A. Tarantola,et al.  Generalized Nonlinear Inverse Problems Solved Using the Least Squares Criterion (Paper 1R1855) , 1982 .

[47]  Filip Neele,et al.  The effect of small‐scale structure on normal mode frequencies and global inversions , 1991 .

[48]  Core-mantle boundary topography and whole-mantle convection , 1989 .

[49]  Barbara Romanowicz,et al.  Comparison of global waveform inversions with and without considering cross-branch modal coupling , 1995 .

[50]  F. D. Stacey.  Physics of the earth , 1977 .

[51]  G. Laske,et al.  A shear - velocity model of the mantle , 1996, Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[52]  T. Tanimoto.  Long-wavelength S-wave velocity structure throughout the mantle , 1990 .

[53]  C. Froidevaux,et al.  Converting mantle tomography into mass anomalies to predict the Earth's radial viscosity , 1994 .

[54]  Jeffrey Park.  Asymptotic coupled-mode expressions for multiplet amplitude anomalies and frequency shifts on an aspherical earth , 1987 .

[55]  Toshiro Tanimoto,et al.  High-resolution global upper mantle structure and plate tectonics , 1993 .

[56]  S. Karato,et al.  Importance of anelasticity in the interpretation of seismic tomography , 1993 .

[57]  D. L. Anderson,et al.  Preliminary reference earth model , 1981 .

[58]  B. Romanowicz.  Multiplet-multiplet coupling due to lateral heterogeneity: asymptotic effects on the amplitude and frequency of the Earth's normal modes , 1987 .

[59]  Toshiro Tanimoto,et al.  Waveforms of long-period body waves in a slightly aspherical earth model , 1993 .