Fine Scale Structure of the Upper Mantle Using Array Technologies

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The internal boundaries (seismic discontinuities) of Earth's upper mantle down todepths of the mantle transition zone at 700 km contain important information aboutthe thermal, compositional and dynamical state of the Earth's interior. High resolutionstudies of this region of the Earth provide important constraints on the internal worksof this planet. Most upper mantle and transition zone studies image structure atintermediate to long wavelength (500 - 1000 km), thus lacking resolution to studystructure at shorter scales (10's km or less). This proposal focuses on using seismicarray data and array processing technologies to improve fine scale resolution of thisregion. A seismic array is a seismometer network that permits analysis of Earthstructure though time series stacking to enhance signal to noise ratios of coherentarrivals over incoherent energy. Improved signal to noise ratios allows studying Earthstructure at short scale lengths. Arrays permit measurement of the incidence angle ofthe wavefield, therefore allowing better phase characterization and identification.Using data from two arrays located in Australia (Warramunga Array) and India(Gauribidanur Array) we target three main objectives: 1) Resolving fine scalestructure of the 410-km and 660-km discontinuities through array analysis of the Pwavetriplication beneath Australia and India; 2) Studying the nature of the 210-kmdiscontinuity beneath oceanic regions using PP scattering; 3) Detection,characterization and modeling of reflectors in the uppermost lower mantle through Pto-P and S-to-P reflections and conversions. Using a large dataset including hundredsof earthquakes recorded at the two arrays will give us an unprecedented resolutionbeneath northern Australia and beneath north and northeast India. The higherresolution will facilitate a more direct comparison to mineral physical andgeodynamical implications including the distribution of water in the mantle, keyfeatures of the mantle transitions zone discontinuities (thickness, seismic velocitygradient, and discontinuity sharpness), the presence or absence of an intermediatedepth discontinuity at 520-km and the existence of partially molten material above410-km depth.