A Finite-frequency Pdiff Kernel Library for Global Tomography Inversions

We compute finite-frequency Pdiff kernels for 1-D reference model AK135 based upon adjoint methods. Each kernel is generated by the interaction of two wave fields, the regular forward wave field and the `adjoint' wave field produced by using the time-reversed velocity at the receiver as a fictitious source, and both fields are computed numerically based upon the Spectral Element Methods (SEM). These sensitivity kernels show unique elliptical patterns on the CMB, and deviate significantly from the theoretical Pdiff ray path. Taking advantage of the fact that the finite-frequency sensitivity kernels depend only on the distance between the source and the receiver for a 1-D reference model, we compute finite-frequency Pdiff kernel libraries for events with depth between the surface and 700 km, and stations at epicentral distances between 100° and 160°. We also investigate the effect of earthquake source radiation pattern on the sensitivity kernels. We use the finite-frequency Pdiff kernels for global Pdiff measurements in a travel-time tomographic inversion, and compare the tomographic images to ones generated using the theoretical Pdiff ray path. Preliminary results indicate that the models from the two theories are quite similar but the finite-frequency inversion leads to a more stable inversion and larger model amplitudes. Thus, by taking into account the finite-frequency effect of the Pdiff travel-time measurements, we believe we improve our ability to resolve the velocity structure of the earth mantle, in particular the structure near the CMB.