Trans-Pacific upper mantle shear velocity structure

摘要: [1] We use 50 Tonga-Fiji events recorded at the broadband TriNet array, southern California, to develop a pure path upper mantle shear velocity model across Pacific. At epicentral distances of 70°–95°, multibounce S waves up S5 are observed, including their triplicated branches, which become particularly clear after stacking. Since these wave multiples turn various depths, simultaneously modeling differential traveltimes and waveforms provides strong constraints on radial structure. We parameterize according priori information from previous oceanic models, so that we can take grid search approach, fully investigate possible interdependencies among parameters. construct synthetics with reflectivity code study both SH SV components. By whole recordings different mechanisms, able separate shallow low-velocity zone (LVZ) features deeper Our preferred (PAC06) contains fast lid (Vsh = 4.78 km s−1, Vsv 4.58 s−1) thickness ∼60 km. The underlying LVZ is prominent lowest velocities Vsh 4.34 4.22 s−1 occurring depth ∼160 These below estimates solid-state LVZ, suggesting presence partial melt. anisotropy (Vsv < Vsh) PAC06 extends ∼300 depth, constrained by turning this depth. Besides 406 651 discontinuities, also has small (∼1%) jump ∼516 consider main be well determined, since explains large data set events. Therefore it ideally suited for comparing mineralogical models.