A new catalogue of normal-mode splitting function measurements up to 10 mHz

Robust constraints on average radial lower mantle anisotropy and consequences for composition and texture

“…The synthetic data for the normal modes thus consisted of 309 (184 + 125) free oscillation centre frequencies. The synthetic data were corrupted by adding Gaussian noise with zero mean and a standard deviation given by the uncertainty estimate for each measurement, as reported by Deuss et al (2013), Koelemeijer et al (2013), Koelemeijer (2014) and on the REM website (http :/ / igppweb .ucsd .edu /~gabi /rem .dir /surface /tmodes .list). We note that the measurement errors were estimated using a cross-validation approach, which may not fully account for any systematic uncertainties.…”

“…Furthermore, PREM was used as a reference model in an iterative damped least-squares inversion of normal-mode spectra for splitting function coefficients, e.g. Deuss et al (2013). As such, the coefficients could in principle be biased towards PREM.…”

“…As such, the coefficients could in principle be biased towards PREM. However, Deuss et al (2013) note that the degree-zero coefficients c 00 , from which the centre frequencies are derived, are the most robust parameters in their inversion, to which no damping is applied; therefore, the bias is assumed to be minimal.…”

Theory and Observations - Seismic Tomography and Inverse Methods

“…Measurements of surface-wave dispersion (i.e., the frequency-dependent surface-wave speed) are key in our understanding of lithospheric structure, especially in oceanic regions where few seismic stations are located (e.g., Debayle et al, 2005;Ekströ m et al, 1997;Laske, 1995;Lévêque and Cara, 1985;Lin and Ritzwoller, 2011;Montagner and Tanimoto, 1991;Nakanishi and Anderson, 1982;Nataf et al, 1986;Ritsema et al, 2004;Trampert and Woodhouse, 1995;van Heijst and Woodhouse, 1999;Visser et al, 2008a;Zhang and Tanimoto, 1993). Normal-mode spectral measurements provide constraints on the longest wavelength part of lateral heterogeneity through the Earth (e.g., Deuss et al, 2011Deuss et al, , 2013Häfner and WidmerSchnidrig, 2013;He and Tromp, 1996;Masters et al, 1982Masters et al, , 1996Resovsky and Ritzwoller, 1999). These data lend themselves for joint inversions for shear and compressional velocity Masters et al, 1996) and even density Tromp, 1999, 2001;Kuo and Romanowicz, 2002).…”

“…Lateral heterogeneity (both elastic heterogeneity and anisotropy) also has a significant effect. Tomographers use observations of splitting to constrain the large-scale variations (e.g., Deuss et al, 2011Deuss et al, , 2013Giardini et al, 1987;He and Tromp, 1996;Ishii and Tromp, 1999;Masters et al, 1996;Resovsky and Ritzwoller, 1999;Ritzwoller et al, 1998), although in general only the 'even-degree' structure of the Earth can be constrained in a direct manner. Splitting measurements are not easy to make.…”