Tomographic filtering of geodynamic models

Seismic tomography and geodynamic modelling are two complementary approaches to further our understanding of Earth's internal structure. Geodynamic models predict the thermal and compositional evolution of the mantle, whereas tomography provides a snapshot of the present state of seismic heterogeneity. By linking both approaches, while including independent constraints from mineral physics, we obtain further insights into the mantle's physical and thermal state.

To enable meaningful comparisons between tomographic and geodynamic models, particularly in terms of the amplitudes, the resolution of the latter need to be adjusted through the use of a tomographic resolution operator. However, previous studies have generally only filtered S-wave structures, which cannot be uniquely interpreted in terms of thermal and chemical variations.

We have extended the tomographic filtering framework of S20RTS (Ritsema et al., Science, 1999) and S40RTS (Ritsema et al., GJI, 2010) and developed the joint SP12RTS filter, which filters both S-wave and P-wave velocity structure (Koelemeijer et al., GJI, 2016; Koelemeijer et al., EPSL, 2018). This filter thus allows us to compare the ratios and correlations of seismic velocities in geodynamic models to global tomography.

Tomographic filtering software:
We provide bash scripts that allow you to convert a geodynamic model into a synthetic tomography model. For this, the seismic velocities in the geodynamic model must be specified in the mantle. The scripts first reparameterise the model into spherical harmonics (laterally) and cubic splines (vertically). Subsequently, this reparameterised model is multiplied with the resolution matrix of the tomographic inversion, resulting in a filtered model.
Scripts and codes are provided to filter only the S-wave velocity structure of a geodynamic model using S20RTS/S40RTS, or to filter both the S-wave and P-wave velocity structures using SP12RTS.
As the files are too large to host here, please get in touch to receive a copy.
If you are using the SP12RTS tomographic filtering software, please reference:
Koelemeijer, P., B.S.A. Schuberth, D.R. Davies, A. Deuss & J. Ritsema (2018). Constraints on the presence of post-perovskite in Earth's lowermost mantle from tomographic-geodynamic model comparisons. Earth Planet. Sci. Lett., Vol. 494, 226-238, doi:10.1016/j.epsl.2018.04.056.
Ritsema, J., A.K. McNamara & A.L. Bull (2007). Tomographic filtering of geodynamic models: Implications for model interpretation and large-scale mantle structure. J. Geophys. Res., Vol. 112, B01303, doi:10.1029/2006JB004566.
Tomographic filtering steps Maps of (left) shear-wave and (right) compressional-wave velocity structure in geodynamic models, showing the high-resolution, reparameterised and filtered models, compared to SP12RTS itself.

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