Synthetic study in amplitude and frequency content of the P410P phases from common upper mantle discontinuity
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We presented the analysis of the amplitude variation in the P410P phases to develop a better understanding of the nature of the 410 km discontinuity. There is debate as to whether it is a phase change in the olivine system or if there is a slight change in mantle chemistry across this boundary. Mineral physicists show that the phase change expected for the olivine system at the depth of 410 km should result in a solid solution of the two phases over a 10 km interval. We therefore produced synthetics to model the expected shape of the P410P phase for different possible velocity gradients that might accompany the gradational phase change. Although we produced synthetics for a 10, 20 and 30 km gradient, the only one expected for the 410 is a 10 km gradient. This modeling was repeated for data low pass filtered at 0.25, 0.5, 0.75 and 1.0 Hz to investigate the frequency response for each of the different gradational boundaries. Real data were analyzed using beam formed data recorded by the EarthScope Transportable array. The P410P functions were produced by simultaneous iterative deconvolution, modified to allow moveout corrections to the cross-correlation functions during each iteration before summing and picking the largest amplitudes.