Observations of core‐mantle boundary Stoneley modes

Abstract

[1] Core-mantle boundary (CMB) Stoneley modes represent a unique class of normal modes with extremely strong sensitivity to wave speed and density variations in the D" region. We measure splitting functions of eight CMB Stoneley modes using modal spectra from 93 events with M w > 7.4 between 1976 and 2011. The obtained splitting function maps correlate well with the predicted splitting calculated for S20RTS+Crust5.1 structure and the distribution of S diff and P diff travel time anomalies, suggesting that they are robust. We illustrate how our new CMB Stoneley mode splitting functions can be used to estimate density variations in the Earth's lowermost mantle. Citation: Koelemeijer, P., A. Deuss, and J. Ritsema (2013), Observations of core-mantle boundary Stoneley modes, Geophys. Res. Lett., 40,

Bayesian inversion of free oscillations for Earth’s radial (an)elastic structure

“…This recent catalogue contains modes sensitive to V P and inner core structure. We supplement this catalogue with similar measurements for Stoneley modes (Koelemeijer et al, 2013) and fundamental modes 0 S 22 À 0 S 30 and the mode 2 S 17 (Koelemeijer, 2014). Note that both centre frequencies and mode quality factors are only sensitive to radial (1-D) structure and thus only depend on the degree-zero splitting function coefficients c 00 .…”

“…In the process, we can assess the uncertainties in the corresponding estimates and the information content of the data. Second, we exploit the constraint on earth model parameters provided by recentlymeasured normal mode splitting functions Koelemeijer et al, 2013;Koelemeijer, 2014). We perform a nonlinear Bayesian inversion of the available data for radial Earth structure in terms of V P ; V S , density, bulk and shear attenuation.…”

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

“…This extensive recent catalogue contains new modes which are sensitive to V P and inner core structure. We supplemented this catalogue with similar measurements for Stoneley modes (Koelemeijer et al, 2013), fundamental modes 0 S 22 -0 S 30 and 2 S 17 (Koelemeijer, 2014). We also experimented with older spheroidal data from the Reference Earth Model (REM) web pages (http :/ /igppweb .ucsd .edu /~gabi /rem .dir /surface /smodes .list).…”

“…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.…”

“…The flexibility enables us to focus on averages of any parameter of interest over an arbitrary depth range (de Wit et al, 2014), rather than focus on the parameters at a given depth, as used by the forward calculation, which are difficult to resolve by the data used. In this study, we used splitting function measurements for spheroidal Koelemeijer et al, 2013;Koelemeijer, 2014) and toroidal (Reference Earth Model, 2001) modes. We focus here on the radial (1-D) seismic structure of the lower mantle and show that this region is indeed anisotropic.…”