Imaging the Anisotropic Shear-wave Velocity Structure of the Earth’s Mantle

Imaging the Anisotropic Shear-wave Velocity Structure of the Earth’s Mantle Over the last 10 years, dozens of new stations of the Global Seismographic Network have been deployed in remote and previously uninstrumented regions. The seismograms recorded at these sites provide new constraints on the structure of the Earth’s mantle. We use seismograms from the years 1994-2003 to build a new set of waveform data to constrain the transversely isotropic shear-wave velocity structure of the mantle. The waveforms are iteratively inverted for earthquake source mechanisms and for the earth structure using the technique of Woodhouse and Dziewónski (1984). Our new data set consists of 219 well-recorded earthquakes and 10 great (Mw ≥ 8) earthquakes. The Harvard CMT solutions of these events are shown in red. Several tens of magnitude 6 earthquakes, which we are also planning to include in the inversion, are shown in blue. All the events distributed throughout the earth recorded by the expanding Global Seismographic Network provide unprecedented global ray-path coverage. The number of seismograms used in the waveform inversion exceeds 120,000 and represents a 60-fold increase compared with the work of Woodhouse and Dziewónski (1984). To further improve resolution in the uppermost and lowermost parts of the mantle, we complement the waveform data set with measurements of surface-wave phase velocities (Ekström et al., 1997) and body-wave travel times (Liu, 1997), respectively. In addition to the anisotropic shear-wave velocity structure, we map the topography of the transition zone discontinuities using measurements of long-period SS precursors (Gu et al., 2003). The new model will improve our knowledge about the structure and dynamics of the Earth’s mantle and will allow for more accurate determination of the earthquake hypocenters and source mechanisms.
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Gu, Y.G., A. M. Dziewónski, and G. Ekström, Simultaneous inversion for mantle shear velocity and topography of transition zone discontinuities, Geophys. J . Int., 154, 559-583, 2003.

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