Graduate Thesis Or Dissertation
 

Seismic wave attenuation of the crust and upper mantle in the Himalaya and South-Central Tibetan Plateau

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/r207tt99m

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  • Recent geophysical and geological investigations of the Tibetan plateau have given rise to conflicting models of plateau growth and deformation, where the presence and extent of partial melt in the crust could be a determining factor. Here we investigate the attenuation structure of the crust and upper mantle, as attenuation is particularly sensitive to temperature and fluids, both aqueous and melts. We present 3D Qp and Qs results of attenuation structure beneath the HiCLIMB array using local earthquakes recorded between 2004 July and 2005 August. Additional synthetic data analysis shows our ability to expand attenuation analysis beyond the traditional use of first-arriving seismic phases to include reflected and refracted arrivals from the Moho and a persistent upper crust velocity interface. Synthetic analysis also reveals a bandwidth-limited window over which source and attenuation can be uniquely determined, improving the precision of attenuation measurements. Results indicate a high Qp,s upper crust, interrupted by moderate to low Qp faulting and evidence for partial fluid saturation to depths of 15 km and full saturation before 30 km depth. Middle and lower crust attenuation is broadly low Qp,s, with evidence for limited partial melt and interrupted by high Qp,s bodies near the termination of the subducting Indian plate and coincident with a sharp decrease in upper mantle Qp. We find little evidence for extensive partial melt in the crust and the sharpness of Q transitions at depth coincident with changes in faulting style in the upper crust suggest strike-slip motion penetrates the crust and upper mantle at the terminus of subduction.
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