Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010geoji.182.1025z&link_type=abstract
Geophysical Journal International, Volume 182, Issue 2, pp. 1025-1042.
Astronomy and Astrophysics
Astronomy
3
Body Waves, Seismic Attenuation, Seismic Tomography, Wave Scattering And Diffraction
Scientific paper
We present a globally distributed data set of ~400000 frequency-dependent SH-wave traveltimes. An automated technique is used to measure teleseismic S, ScS and SS traveltimes at several periods ranging from 10 to 51 s. The targeted seismic phases are first extracted from the observed and synthetic seismograms using an automated time window algorithm. Traveltimes are then measured at several periods, by cross-correlation between the selected observed and synthetic filtered waveforms. Frequency-dependent effects due to crustal reverberations beneath each receiver are handled by incorporating crustal phases into WKBJ synthetic waveforms.
After correction for physical dispersion due to intrinsic anelastic processes, we observe a residual traveltime dispersion on the order of 1-2 s in the period range of analysis. This dispersion occurs differently for S, ScS and SS, which is presumably related to their differing paths through the Earth. We find that: (1) Wavefront-healing phenomenon is observed for S and to a lesser extent SS waves having passed through very low velocity anomalies. (2) A preferred sampling of high velocity scatterers located at the CMB may explain our observation that ScS waves travel faster at low-frequency than at high-frequency. (3) A frequency-dependent attenuation q(ω) ~ q0 × ω-α, with α ~ 0.2, is compatible with the globally averaged dispersion observed for S waves.
Debayle Eric
Sambridge Malcolm
Zaroli Christophe
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