The Relative Behavior of Shear Velocity, Bulk Sound Speed, and Compressional Velocity in the Mantle: Implications for Chemical and Thermal Structure

Despite immense progress in imaging seismic velocity anomalies in the mantle over the past 15 years, we still know relatively little about their physical cause. One way to shed some light on this problem is to investigate the relative amplitudes of compressional and shear velocity anomalies in the mantle. Unfortunately, the amplitudes of velocity anomalies can be quite sensitive to the data sets and imaging techniques employed. It is therefore usually meaningless to take two models from the literature and do a simple comparison, In this paper, we consider joint modeling of P and S data sets and compare with some recent results from the literature. Some robust patterns are beginning to emerge which allow us to identify regions of the lower mantle which are anomalous. Such regions seem to be associated with large-scale upwelling in the mantle and may indicate chemical interaction with the core.

[1]  Don L. Anderson,et al.  Travel times and station corrections for P waves at teleseismic distances , 1983 .

[2]  Don W. Vasco,et al.  Tomographic inversions for mantle P wave velocity structure based on the minimization of l 2 and l 1 norms of International Seismological Centre Travel Time Residuals , 1993 .

[3]  D. Giardini,et al.  Three-dimensional structure of the Earth from splitting in free-oscillation spectra , 1987, Nature.

[4]  D. York.  Least-squares fitting of a straight line. , 1966 .

[5]  G. Masters,et al.  Constraints on global phase velocity maps from long-period polarization data , 1996 .

[6]  Gabi Laske,et al.  CRUST 5.1: A global crustal model at 5° × 5° , 1998 .

[7]  E. R. Engdahl,et al.  Evidence for deep mantle circulation from global tomography , 1997, Nature.

[8]  John A. Orcutt,et al.  Axi-symmetric Earth models and inner-core anisotropy , 1988, Nature.

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

[10]  Joseph S. Resovsky,et al.  Regularization uncertainty in density models estimated from normal mode data , 1999 .

[11]  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.

[12]  G. Masters,et al.  Constraining aspherical structure with low-degree interaction coefficients: Application to uncoupled multiplets , 1988 .

[13]  Wei-jia Su,et al.  Simultaneous inversion for 3-D variations in shear and bulk velocity in the mantle , 1997 .

[14]  Thomas H. Jordan,et al.  Aspherical Earth structure from fundamental spheroidal-mode data , 1982, Nature.

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

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

[17]  G. Nolet,et al.  Seismic wave propagation and seismic tomography , 1987 .

[18]  Andrea Morelli,et al.  Anisotropy of the inner core inferred from PKIKP travel times , 1986 .

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

[20]  J. Woodhouse,et al.  A worldwide comparison of predicted S-wave delays from a three-dimensional upper mantle model with P-wave station corrections , 1985 .

[21]  B. Kennett,et al.  Traveltimes for global earthquake location and phase identification , 1991 .

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

[23]  R. Hilst,et al.  Compositional heterogeneity in the bottom 1000 kilometers of Earth's mantle: toward a hybrid convection model , 1999, Science.

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

[25]  Jeroen Tromp,et al.  Measurements and global models of surface wave propagation , 1997 .

[26]  Jeroen Tromp,et al.  Normal-mode constraints on the structure of the Earth , 1996 .

[27]  Joseph S. Resovsky,et al.  New and refined constraints on three‐dimensional Earth structure from normal modes below 3 mHz , 1998 .

[28]  Harmen Bijwaard,et al.  Closing the gap between regional and global travel time tomography , 1998 .

[29]  A. Dziewoński,et al.  Global Images of the Earth's Interior , 1987, Science.

[30]  Thorne Lay,et al.  The core–mantle boundary layer and deep Earth dynamics , 1998, Nature.

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

[32]  Hua-wei Zhou,et al.  A high-resolution P wave model for the top 1200 km of the mantle , 1996 .

[33]  E. Engdahl,et al.  Global teleseismic earthquake relocation with improved travel times and procedures for depth determination , 1998, Bulletin of the Seismological Society of America.

[34]  Yosihiko Ogata,et al.  Whole mantle P-wave travel time tomography , 1990 .

[35]  Andrea Morelli,et al.  Topography of the core–mantle boundary and lateral homogeneity of the liquid core , 1987, Nature.

[36]  Don W. Vasco,et al.  Formal inversion of ISC arrival times for mantle P-velocity structure , 1993 .

[37]  Jeannot Trampert,et al.  High resolution global phase velocity distributions , 1996 .

[38]  G. Masters,et al.  Upper mantle structure from long-period differential traveltimes and free oscillation data , 1992 .

[39]  G. Masters,et al.  Aspherical structure constraints from free oscillation frequency and attenuation measurements , 1989 .

[40]  Olafur Gudmundsson,et al.  Stochastic analysis of global traveltime data: mantle heterogeneity and random errors in the ISC data , 1990 .

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

[42]  T. Lay,et al.  Global surface wave phase velocity variations , 1996 .

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

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

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

[46]  Barbara Romanowicz,et al.  Global mantle shear velocity model developed using nonlinear asymptotic coupling theory , 1996 .

[47]  J. Tromp,et al.  Normal-mode and free-Air gravity constraints on lateral variations in velocity and density of Earth's mantle , 1999, Science.

[48]  Andrea Morelli,et al.  Body wave traveltimes and a spherically symmetric P- and S-wave velocity model , 1993 .

[49]  E. R. Engdahl,et al.  Constraints on seismic velocities in the Earth from traveltimes , 1995 .

[50]  D. Vasco,et al.  Lateral variations in mantle velocity structure and discontinuities determined from P, PP, S, SS, and SS — SdS travel time residuals , 1995 .

[51]  D. Giardini,et al.  The relative amplitudes of mantle heterogeneity in P velocity, S velocity and density from free-oscillation data , 1991 .

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

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

[54]  A. Agnon,et al.  δs at high pressure and dlnVs/dlnVp in the lower mantle , 1990 .

[55]  B. Kennett,et al.  Joint seismic tomography for bulk sound and shear wave speed in the Earth's mantle , 1998 .

[56]  D. L. Anderson,et al.  Importance of Physical Dispersion in Surface Wave and Free Oscillation Problems: Review (Paper 6R0680) , 1977 .

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

[58]  J. Woodhouse,et al.  Ratio of relative S to P velocity heterogeneity in the lower mantle , 1996 .

[59]  J. Woodhouse,et al.  Evidence for proportionality of P and S heterogeneity in the lower mantle , 1995 .

[60]  D. Vasco,et al.  Whole Earth structure estimated from seismic arrival times , 1998 .

[61]  O. Anderson,et al.  The relationship between shear and compressional velocities at high pressures: Reconciliation of seismic tomography and mineral physics , 1992 .

[62]  Don W. Vasco,et al.  Robust inversion of IASP91 travel time residuals for mantle P and S velocity structure, earthquake mislocations, and station corrections , 1994 .

[63]  R. Lytle,et al.  Computerized geophysical tomography , 1979, Proceedings of the IEEE.

[64]  W. Peltier,et al.  Plate tectonics and aspherical earth structure: The Importance of poloidal‐toroidal coupling , 1987 .