Van Camp, M. ; de Viron, O. ; Ferreira, A.M.G.

Poster presented at AGU 2019 Fall Meeting, San Francisco on 2019-12-10

Abstract: Classical analysis of new tomography models consists in a comparison with others by correlation, spectral profiles, or localisation of patterns. To interpret the models in a quantitative, objective way and ease comparisons, we analyse the model information using principal component (PC) analysis. The varimax criterion applied to the PCs separates modes associated with different depth ranges. This enables determining the importance of different parts of the tomography models when reconstructing them. We apply this method to the isotropic part of 6 global shear-wave speed models: SAVANI (Auer et al., 2014), S20RTS (Ritsema et al., 1999), S40RTS (Ritsema et al., 2011), SEMUCB-WM1 (French & Romanowicz, 2014), SGLOBE-rani (Chang et al., 2015), and S362WMANI+M (Moulik & Ekstrom, 2014). According to the models, the method generates 7 to 15 independent varimax PCs, capturing more than 97% of the total information. A comparison of the PCs with the information extracted from the full models shows that no interpretable information is lost. Each mode is composed of a vertical anomaly profile, to which we associate a horizontal pattern by orthogonal projection. The maximum of the depth profile and the geographical distribution of the horizontal pattern enable examining the key characteristics of the main components of the models. For a fair comparison, we also compute a varimax PCA on a concatenation of the 6 models together. This imposes a projection of the average vertical profile, which allows for a mode-by-mode comparison between the model set. Similar main regions are identified when applying the analysis either to the individual tomography models or to the concatenation of the models: (i) Large Low Shear Velocity Provinces (LLSVPs); (ii) Mid-lower mantle (~1,200 km depth) showing some deep subduction signals and low-velocity anomalies beneath the Pacific and Africa, possibly associated with mantle plumes; (iii) Uppermost lower mantle (~800 km depth), also with deep subduction and low-velocity in the southeastern Pacific ocean; (iv) Transition zone (~400 km depth), showing subduction and low velocity anomalies beneath the Pacific and Indian oceans; and, (v) ridges and cratons in the uppermost upper mantle (~200 km depth). We discuss the significance and potential implications of these main regions that are identified.

Keyword(s): Seismic Tomography ; Principal Component Analysis ; Earth's interior
Note: Collaborative work with U. La Rochelle