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Data Services Products: EMC-ReferenceModels IRIS EMC - Reference Earth Models


Most of the EMC Earth models are expressed as perturbations relative to a particular 1-D reference Earth model. This page provides access to some reference Earth models that are hosted by EMC or hosted externally.


Below is a collection of reference models some of which, as indicated, are used as the starting model for computation of the tomographic models.

EMC-hosted reference Earth models

PREM (referenced by GyPSum, SAW24B16 and as PREM500 by SAW642AN and SAW642ANb ) The Preliminary Reference Earth Model, Dziewonski and Anderson (1981) , is an average Earth model that incorporates anelastic dispersion and anisotropy and therefore it is frequency-dependent and transversely isotropic for the upper mantle.
PEM Parametric Earth Models (PEM) — Three models (Average, Continental & Oceanic) that were introduced by Dziewonski, Hales and Lapwood (1975) for which the radial variations of density and velocity are represented by piecewise continuous analytical functions of radius. All three models are identical below a depth of 420 km.
ak135-f ak135-f is a variant of the ak135 velocity model, Kennett, Engdahl & Buland (1995) , which is obtained by augmenting it with the density and Q model of Montagner & Kennett (1995).
iasp91 The iasp91 reference model is a parameterised velocity model that has been constructed to be a summary of the travel time characteristics of the main seismic phases, Kennett and Engdahl (1991).
MC35 (referenced by NA04 & NA07 ) MC35 is a 1-D averaged Earth model based on the continental Earth model PEM-C with its uppermost mantle S-wave velocity, down to 210 km, set to a constant value of 4.5 km/s, replacing the high- and low velocity zone of PEM-C , van der Lee and Nolet (1997).
STW105 (referenced by S362ANI & S362WMANI) STW105 (also known as REF) is a transversely isotropic reference Earth model, Kustowski, Ekstrom and Dziewonski (2008).
TNA/SNA (referenced by GyPSum ) — This model is an average of the TNA (Tectonic North America) and SNA (Shield North America) models of Grand and Helmberger (1984).

Externally-hosted reference Earth models

CRUST1.0 CRUST1.0 is a new global crustal model, Laske et al. (2013) , specified on a 1×1 degree grid and incorporates an updated version of the global sediment thickness. The higher-resolution CRUST1.0 supersedes the older CRUST2.0 model.
CRUST2.0 CRUST2.0 is a global crustal model, Bassin et al. (2000) , that specifies density, compressional and shear velocity on a 2°x2° grid. This model is updated version of the CRUST5.1 model of Mooney et al. (1998).


  • Trabant, C., A. R. Hutko, M. Bahavar, R. Karstens, T. Ahern and R. Aster (2012), Data products at the IRIS DMC: stepping-stones for research and other application, Seismological Research Letters, 83(6), 846:854. doi:10.1785/0220120032
  • The corresponding Earth model reference:
    • Bassin, C., G. Laske, and G. Masters. 2000. “The Current Limits of Resolution for Surface Wave Tomography in North America.” EOS, Trans. Am. Geophys. Un. 81, F897.
    • Dziewonski, A.M., and D.L. Anderson. 1981. “Preliminary reference Earth model.” Phys. Earth Plan. Int. 25:297-356.
    • Dziewonski, A.M., A.L. Hales, and E.R. Lapwood. 1975. “Parametrically simple earth models consistent with geophysical data Phys.” Earth Plan. Int. 10:12.
    • Grand, S.P., and D.V. Helmberger. 1984. “Upper mantle shear structure of North America.” Geophys. J. R. Astr. Soc. 76:399-438.
    • Kennett B.L.N. and Engdahl E.R. 1991. “Travel times for global earthquake location and phase association.” Geophysical Journal International, 105:429-465.
    • Kennett B.L.N., Engdahl E.R. and Buland R. 1995. “Constraints on seismic velocities in the earth from travel times” Geophys. J. Int. 122:108-124.
    • Kustowski, B, G. Ekstrom, and A. M. Dziewonski. 2008. “Anisotropic shear-wave velocity structure of the Earth’s mantle: A global model” J. Geophys. Res., 113:B06306, doi:10.1029/2007JB005169.
    • Laske, G., G. Masters., Z. Ma, and M. Pasyanos. 2013. “Update on CRUST1.0 – A 1-degree Global Model of Earth’s Crust” Geophys. Res. Abstracts, 15, Abstract EGU2013-2658, 2013.
    • Mooney, W.D., G. Laske, and G. Masters. 1998. “A global crustal model at 5×5 degrees.” J. Geophys. Res. 103:727-747.
    • Van der Lee, S. and Guust Nolet 1997. “Upper mantle S-velocity structure of North America.” J. Geophys. Res. 102:22815-22838.
    • Montagner J.P. & Kennett B.L.N. 1995. “How to reconcile body-wave and normal-mode reference Earth models?” Geophys. J. Int. 125:229-248.


  • The research community for their contributions and product review