SP12RTS: a degree-12 model of shear- and compressional-wave velocity for Earth's mantle (original) (raw)

Abstract

We present the new model SP12RTS of isotropic shear-wave (V S) and compressional-wave (V P) velocity variations in the Earth's mantle. SP12RTS is derived using the same methods as employed in the construction of the shear-wave velocity models S20RTS and S40RTS, and the same data types. SP12RTS includes additional traveltime measurements of P-waves and new splitting measurements: 33 normal modes with sensitivity to the compressional-wave velocity and 9 Stoneley modes with sensitivity primarily to the lowermost mantle. Contrary to S20RTS and S40RTS, variations in V S and V P are determined without invoking scaling relationships. Lateral velocity variations in SP12RTS are parametrised using spherical harmonics up to degree 12, to focus on long-wavelength features of V S and V P and their ratio R. Largelow-velocity provinces (LLVPs) are observed for both V S and V P. SP12RTS also features an increase of R up to 2500 km depth, followed by a decrease towards the core-mantle boundary. A negative correlation between the shear-wave and bulk-sound velocity variations is observed for both the LLVPs and the surrounding mantle. These characteristics can be explained by the presence of post-perovskite or large-scale chemical heterogeneity in the lower mantle. 2 Koelemeijer et al.

Loading...

Loading Preview

Sorry, preview is currently unavailable. You can download the paper by clicking the button above.

References (77)

  1. Antolik, M., Gu, Y. J., Ekström, G., & Dziewonski, A. M., 2003. J362D28: A new joint model of com- pressional and shear velocity in the Earth's mantle, Geophys. J. Int., 153(2), 443-466.
  2. Auer, L., Boschi, L., Becker, T., Nissen-Meyer, T., & Giardini, D., 2014. Savani: A variable resolution whole-mantle model of anisotropic shear velocity variations based on multiple data sets, J. Geophys. Res., 119(4), 3006-3034.
  3. Bassin, C., Laske, G., & Masters, G., 2000. The current limits of resolution for surface wave tomography in North America, Eos Trans. AGU, F987(81).
  4. Boschi, L. & Dziewonski, A. M., 2000. Whole Earth tomography from delay times of P, PcP, and PKP phases: Lateral heterogeneities in the outer core or radial anisotropy in the mantle?, J. Geophys. Res., 105(B6), 13675-13696.
  5. Bower, D. J., Gurnis, M., & Seton, M., 2013. Lower mantle structure from paleogeographically constrained dynamic Earth models, Geophys. Geochem. Geosys., 14(1), 44-63.
  6. Chang, S.-J., Ferreira, A. M., Ritsema, J., Heijst, H. J., & Woodhouse, J. H., 2015. Joint inversion for global isotropic and radially anisotropic mantle structure including crustal thickness perturbations, Journal of Geophysical Research: Solid Earth.
  7. Cobden, L., Thomas, C., & Trampert, J., 2014. Seismic detection of post-perovskite inside the Earth, The Earth's heterogeneous mantle.
  8. Davaille, A., 1999. Simultaneous generation of hotspots and superswells by convection in a heterogeneous planetary mantle, Nature, 402(6763), 756-760.
  9. Davies, D. & Davies, J., 2009. Thermally-driven mantle plumes reconcile multiple hot-spot observations, Earth Planet. Sci. Lett., 278(1), 50-54.
  10. Davies, D., Goes, S., Davies, J., Schuberth, B., Bunge, H., & Ritsema, J., 2012. Reconciling dy- namic and seismic models of Earth's lower mantle: The dominant role of thermal heterogeneity, Earth Planet. Sci. Lett., 353, 253-269.
  11. Della Mora, S., Boschi, L., Tackley, P., Nakagawa, T., & Giardini, D., 2011. Low seismic resolution cannot explain S/P decorrelation in the lower mantle, Geophys. Res. Lett., 38(12).
  12. Deschamps, F. & Tackley, P. J., 2009. Searching for models of thermo-chemical convection that explain probabilistic tomography: II. Influence of physical and compositional parameters, Phys. Earth Planet. In- ter., 176(1), 1-18.
  13. Deschamps, F., Trampert, J., & Tackley, P., 2007. Thermo-chemical structure of the lower mantle: seismo- logical evidence and consequences for geodynamics, Superplume: Beyond Plate Tectonics, pp. 293-320.
  14. Deuss, A., Ritsema, J., & van Heijst, H.-J., 2013. A new catalogue of normal-mode splitting function measurements up to 10 mHz, Geophys. J. Int., 192(3).
  15. Dziewonski, A. & Anderson, D., 1981. Preliminary reference Earth model, Phys. Earth Planet. Inter., 25(4), 297-356.
  16. Dziewonski, A. M., Hager, B. H., & O'Connell, R. J., 1977. Large-scale heterogeneities in the lower mantle, J. Geophys. Res., 82(2), 239-255.
  17. Dziewonski, A. M., Lekić, V., & Romanowicz, B. A., 2010. Mantle anchor structure: An argument for bottom up tectonics, Earth Planet. Sci. Lett., 299(1), 69-79.
  18. Edmonds, A., 1960. Angular momentum in quantum mechanics, Princeton University Press.
  19. Ferreira, A., Woodhouse, J., Visser, K., & Trampert, J., 2010. On the robustness of global radially anisotropic surface wave tomography, J. Geophys. Res., 115(B4).
  20. French, S., Lekić, V., & Romanowicz, B., 2013. Waveform tomography reveals channeled flow at the base of the oceanic asthenosphere, Science, 342(6155), 227-230.
  21. Garnero, E. & McNamara, A., 2008. Structure and dynamics of Earth's lower mantle, Science, 320(5876), 626.
  22. Gilbert, F. & Dziewonski, A., 1975. An application of normal mode theory to the retrieval of structural parameters and source mechanisms from seismic spectra, Phil. Trans. R. Soc. Lond., 278(1280), 187-269.
  23. Grocholski, B., Catalli, K., Shim, S.-H., & Prakapenka, V., 2012. Mineralogical effects on the detectability of the postperovskite boundary, Proc. Natl. Acad. Sci. USA, 109(7), 2275-2279.
  24. Gu, Y. J., Dziewonski, A. M., Su, W., & Ekström, G., 2001. Models of the mantle shear velocity and discontinuities in the pattern of lateral heterogeneities, J. Geophys. Res., 106(B6), 11169-11199.
  25. Houser, C., Masters, G., Shearer, P., & Laske, G., 2008. Shear and compressional velocity models of the mantle from cluster analysis of long-period waveforms, Geophys. J. Int., 174(1), 195-212.
  26. Iitaka, T., Hirose, K., Kawamura, K., & Murakami, M., 2004. The elasticity of the MgSiO3 post-perovskite phase in the Earth's lowermost mantle, Nature, 430(6998), 442-445.
  27. Ishii, M. & Tromp, J., 1999. Normal-mode and free-air gravity constraints on lateral variations in velocity and density of Earth's mantle, Science, 285(5431), 1231.
  28. Ishii, M. & Tromp, J., 2001. Even-degree lateral variations in the Earth's mantle constrained by free oscillations and the free-air gravity anomaly, Geophys. J. Int., 145(1), 77-96.
  29. Karato, S., 1993. Importance of anelasticity in the interpretation of seismic tomography, Geo- phys. Res. Lett., 20(15), 1623-1626.
  30. Karato, S.-i. & Karki, B. B., 2001. Origin of lateral variation of seismic wave velocities and density in the deep mantle, J. Geophys. Res., 106(R10), 21771-21783.
  31. Koelemeijer, P., Deuss, A., & Ritsema, J., 2013. Observations of core-mantle boundary Stoneley modes, Geophys. Res. Lett., 40(11), 2557-2561.
  32. Koelemeijer, P., Deuss, A., & Ritsema, J., 2015. Density structure of Earth's lowermost mantle from Stoneley mode splitting observations, Submitted to Nature Geosci..
  33. Koelemeijer, P. J., 2014. Normal mode studies of long wavelength structures in Earth's lowermost mantle, PhD thesis, University of Cambridge.
  34. Kustowski, B., Ekström, G., & Dziewoński, A., 2008. Anisotropic shear-wave velocity structure of the Earth's mantle: A global model, J. Geophys. Res., 113(B6).
  35. Lay, T. & Garnero, E. J., 2011. Deep mantle seismic modeling and imaging, Ann. Rev. Earth Planet Sci., 39, 91-123.
  36. Lay, T., Hernlund, J., & Buffett, B., 2008. Core-mantle boundary heat flow, Nature Geosci., 1(1), 25-32.
  37. Lekić, V., Cottaar, S., Dziewonski, A., & Romanowicz, B., 2012. Cluster analysis of global lower mantle tomography: A new class of structure and implications for chemical heterogeneity, Earth Planet. Sci. Lett., 357, 68-77.
  38. Li, C., van der Hilst, R. D., Engdahl, E. R., & Burdick, S., 2008. A new global model for P wave speed variations in Earth's mantle, Geophys. Geochem. Geosys., 9(5).
  39. Li, X., Giardini, D., & Woodhouse, J., 1991a. The relative amplitudes of mantle heterogeneity in P velocity, S velocity and density from free-oscillation data, Geophys. J. Int., 105(3), 649-657.
  40. Li, X., Giardini, D., & Woodhouses, J., 1991b. Large-scale three-dimensional even-degree structure of the Earth from splitting of long-period normal modes, J. Geophys. Res., 96(B1), 551-577.
  41. Malcolm, A. E. & Trampert, J., 2011. Tomographic errors from wave front healing: more than just a fast bias, Geophys. J. Int., 185(1), 385-402.
  42. Masters, G., Laske, G., Bolton, H., & Dziewonski, A., 2000. The relative behavior of shear velocity, bulk sound speed, and compressional velocity in the mantle: Implications for chemical and thermal structure, Geophys. Monograph AGU, 117, 63-87.
  43. McNamara, A., Garnero, E., & Rost, S., 2010. Tracking deep-mantle reservoirs with ultra-low-velocity zones, Earth Planet. Sci. Lett., 299(1), 1-9.
  44. McNamara, A. K. & Zhong, S., 2005. Thermochemical structures beneath Africa and the Pacific Ocean, Nature, 437(7062), 1136-1139.
  45. Menke, W., 1989. Geophysical data analysis: discrete inverse theory, Geophysical Data Analysis, Aca- demic, San Diego, California.
  46. Mosca, I., Cobden, L., Deuss, A., Ritsema, J., & Trampert, J., 2012. Seismic and mineralogical structures of the lower mantle from probabilistic tomography, J. Geophys. Res., 117(B6), B06304.
  47. Murakami, M., Hirose, K., Kawamura, K., Sata, N., & Ohishi, Y., 2004. Post-perovskite phase transition in MgSiO3, Science, 304(5672), 855.
  48. Nakagawa, T. & Tackley, P. J., 2014. Influence of combined primordial layering and recycled MORB on the coupled thermal evolution of Earth's mantle and core, Geophys. Geochem. Geosys., 15(3), 619-633.
  49. Nakagawa, T., Tackley, P. J., Deschamps, F., & Connolly, J. A., 2012. Radial 1-D seismic structures in the deep mantle in mantle convection simulations with self-consistently calculated mineralogy, Geophys. Geochem. Geosys., 13(11).
  50. Nolet, G. & Moser, T.-J., 1993. Teleseismic delay times in a 3-d earth and a new look at the s discrepancy, Geophys. J. Int., 114(1), 185-195.
  51. Oganov, A. & Ono, S., 2004. Theoretical and experimental evidence for a post-perovskite phase of Mg- SiO3 in Earth's D" layer, Nature, 430(6998), 445-448.
  52. Ohta, K., Hirose, K., Lay, T., Sata, N., & Ohishi, Y., 2008. Phase transitions in pyrolite and MORB at lowermost mantle conditions: implications for a MORB-rich pile above the core-mantle boundary, Earth Planet. Sci. Lett., 267(1), 107-117.
  53. Panning, M. & Romanowicz, B., 2006. A three-dimensional radially anisotropic model of shear velocity in the whole mantle, Geophys. J. Int., 167(1), 361-379.
  54. Panning, M., Lekić, V., & Romanowicz, B., 2010. Importance of crustal corrections in the development of a new global model of radial anisotropy, J. Geophys. Res., 115(B12).
  55. Resovsky, J. & Ritzwoller, M., 1999. Regularization uncertainty in density models estimated from normal mode data, Geophys. Res. Lett., 26(15), 2319-2322.
  56. Resovsky, J. & Trampert, J., 2003. Using probabilistic seismic tomography to test mantle velocity-density relationships, Earth Planet. Sci. Lett., 215(1-2), 121-134.
  57. Ritsema, J. & van Heijst, H.-J., 2002. Constraints on the correlation of P-and S-wave velocity heterogene- ity in the mantle from P, PP, PPP and PKPab traveltimes, Geophys. J. Int., 149(2), 482-489.
  58. Ritsema, J., van Heijst, H.-J., & Woodhouse, J., 1999. Complex shear wave velocity structure imaged beneath Africa and Iceland, Science, 286(5446), 1925.
  59. Ritsema, J., van Heijst, H.-J., & Woodhouse, J. H., 2004. Global transition zone tomography, J. Geo- phys. Res., 109(B2).
  60. Ritsema, J., Deuss, A., van Heijst, H.-J., & Woodhouse, J. H., 2011. S40RTS: a degree-40 shear-velocity model for the mantle from new Rayleigh wave dispersion, teleseismic traveltime and normal-mode split- ting function measurements, Geophys. J. Int., 184(3), 1223-1236.
  61. Romanowicz, B., 2001. Can we resolve 3D density heterogeneity in the lower mantle?, Geophys. Res. Lett., 28(6), 1107-1110.
  62. Saltzer, R., van der Hilst, R., & Karason, H., 2001. Comparing P and S wave heterogeneity in the mantle, Geophys. Res. Lett., 28(7), 1335-1338.
  63. Schuberth, B., Bunge, H.-P., Steinle-Neumann, G., Moder, C., & Oeser, J., 2009. Thermal versus elastic heterogeneity in high-resolution mantle circulation models with pyrolite composition: High plume excess temperatures in the lowermost mantle, Geophys. Geochem. Geosys., 10(1).
  64. Schuberth, B., Zaroli, C., & Nolet, G., 2012. Synthetic seismograms for a synthetic Earth: long-period P-and S-wave traveltime variations can be explained by temperature alone, Geophys. J. Int., 188(3), 1393-1412.
  65. Simmons, N. A., Forte, A. M., Boschi, L., & Grand, S. P., 2010. GyPSuM: A joint tomographic model of mantle density and seismic wave speeds, J. Geophys. Res., 115(B12).
  66. Soldati, G., Boschi, L., & Forte, A., 2012. Tomography of core-mantle boundary and lowermost mantle coupled by geodynamics, Geophys. J. Int., 189(2), 730-746.
  67. Su, W. & Dziewonski, A., 1997. Simultaneous inversion for 3-D variations in shear and bulk velocity in the mantle, Phys. Earth Planet. Inter., 100(1-4), 135-156.
  68. Tarantola, A., 1987. Inverse problem theory, Elsevier, Amsterdam.
  69. Tateno, S., Hirose, K., Sata, N., & Ohishi, Y., 2007. Solubility of FeO in (Mg,Fe)SiO3 perovskite and the post-perovskite phase transition, Phys. Earth Planet. Inter., 160(3), 319-325.
  70. Trampert, J., Deschamps, F., Resovsky, J., & Yuen, D., 2004. Probabilistic tomography maps chemical heterogeneities throughout the lower mantle, Science, 306(5697), 853.
  71. Tsuchiya, T., Tsuchiya, J., Umemoto, K., & Wentzcovitch, R., 2004. Phase transition in MgSiO3 per- ovskite in the Earth's lower mantle, Earth Planet. Sci. Lett., 224(3-4), 241-248.
  72. van Heijst, H. J. & Woodhouse, J., 1997. Measuring surface-wave overtone phase velocities using a mode- branch stripping technique, Geophys. J. Int., 131(2), 209-230.
  73. van Heijst, H.-J. & Woodhouse, J., 1999. Global high-resolution phase velocity distributions of overtone and fundamental-mode surface waves determined by mode branch stripping, Geophys. J. Int., 137(3), 601-620.
  74. Wessel, P. & Smith, W., 1998. New, improved version of the generic mapping tools released, Eos Trans. AGU, 79, 579-579.
  75. Woodhouse, J., Giardini, D., & Li, X., 1986. Evidence for inner core anisotropy from free oscillations, Geophys. Res. Lett., 13(13), 1549-1552.
  76. Wookey, J., Stackhouse, S., Kendall, J.-M., Brodholt, J., & Price, G. D., 2005. Efficacy of the post- perovskite phase as an explanation for lowermost-mantle seismic properties, Nature, 438(7070), 1004- 1007.
  77. Young, M., Tkalcić, H., Bodin, T., & Sambridge, M., 2013. Global P wave tomography of Earth's low- ermost mantle from partition modeling, Journal of Geophysical Research: Solid Earth, 118(10), 5467- 5486.