Seismic migration processing of P-SV converted]phases for mantle discontinuity structure beneath the Snake River Plain, western United States

We experiment with backprojection migration processing of teleseismic recei ver functions from the Snake River Plain (SRP) broadband seismic experiment . Previous analyses of data from this experiment have used a common midpoin t (CMP) stacking approach, a method widely applied for analysis of P-SV con verted phases (receiver functions) to obtain high-resolution imaging of upp er mantle discontinuities. The CMP technique assumes that all P-SV conversi ons are produced by flat-lying structures and may not properly image dippin g, curved, or laterally discontinuous interfaces. In this paper we adopt a backprojection migration scheme to solve for an array of point scatterers t hat best produces the large suite of observed receiver functions. We first perform synthetic experiments that illustrate the potential improvement of migration processing over CMP stacks. Application of the migration processi ng to the SRP data set shows most of the major features as in the original CMP work, hut with a weaker 410-km discontinuity and a more intermittent di scontinuity at 250 km apparent depth. Random resampling tests are also perf ormed to assess the robustness of subtle features in our discontinuity imag es. These tests show that a 20-km elevation of the 660-km discontinuity dir ectly beneath the Snake River Plain is robust, but that the variations in 4 10-km discontinuity topography that we observe are not stable upon resampli ng. "Bright spots" near 250 km apparent depth are robust upon resampling, b ut interpretation of these features is complicated by possible sidelobe art ifacts from topside Moho reverberations.