Empirical transfer functions: Application to determination of outermost core velocity structure using SmKS phases

Abstract

[1] SmKS waves provide good resolution of outer-core velocity structure, but are affected by heterogeneity in the D 00 region. We have developed an Empirical Transfer Function (ETF) technique that transforms a reference pulse (here, SmKS) into a target waveform (SKKS) by: (1) timewindowing the respective pulses, (2) applying Wiener deconvolution, and (3) convolving the output with a Gaussian waveform. Common source and path effects are implicitly removed by this process. We combine ETFs from 446 broadband seismograms to produce a global stack, from which S3KS-SKKS differential time can be measured accurately. As a result of stacking, the scatter in our measurements (0.43 s) is much less than the 1.29 s scatter in previous compilations. Although our data do not uniquely constrain outermost core velocities, we show that the fit of most standard models can be improved by perturbing the outermost core velocity. Our best-fitting model is formed using IASP91 with PREM-like velocity at the top of the core. Citation: Alexandrakis, C., and D. W. Eaton (2007), Empirical transfer functions: Application to determination of outermost core velocity structure using SmKS phases, Geophys.

Array‐Based Iterative Measurements of Travel Times and Their Constraints on Outermost Core Structure

“…However, the conclusions of various studies are not consistent. For example, Alexandrakis and Eaton (2007) exploited the Empirical Transfer Function technique to precisely measure SmKS differential travel times and found no evidence for stratification, consistent with some other SmKS studies (e.g., Alexandrakis & Eaton, 2010;Souriau & Poupinet, 1991a). In contrast, other reports support a layer with lower Vp than that of PREM in the outermost core (e.g., Eaton & Kendall, 2006;Garnero et al, 1993;Helffrich & Kaneshima, 2010;Kaneshima & Matsuzawa, 2015;Kaneshima, 2018;Tanaka, 2004Tanaka, , 2007Tang et al, 2015), although the thickness and amplitude of the Vp anomaly varies from one study to another.…”

Effects of a radially varying electrical conductivity on 3D numerical dynamos

“…Seismological constraints have been so far inconclusive. However, recent seismological results using outermost core waveforms seem to be consistent with the existence of a low density layer of about 100 km thickness (Alexandrakis and Eaton, 2007;Tanaka, 2007) It has been confirmed that Mercury has a liquid iron core (Margot et al, 2007). Furthermore, it is likely that Mercury's weak intrinsic magnetic field is generated by a dynamo in its liquid outer core.…”