Full-Waveform Sensitivity Kernels of Component-Differential Traveltimes and ZH Amplitude Ratios for Velocity and Density Tomography

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Previous studies of the Rayleigh wave vertical-to-horizontal amplitude ratios (ZH ratio) assumed one-dimensional velocity and density structures beneath the receiver, neglecting the effects of three-dimensional (3-D) heterogeneities on wave amplitudes. Those studies have well demonstrated that the ZH ratios provide powerful constraints on the crust and mantle structure. However, the azimuthal averaging of the ZH ratios common in those studies means reduced sensitivities to the 3-D structure and thus the ZH ratios' potential resolving power. We derive equations for the 3-D full-wave sensitivity kernels of the ZH ratio and differential traveltime of the vertical and radial components of Rayleigh and P waves, to perturbations in shear and compressional velocities and density. The kernels are calculated based on finite difference modeling of wave propagation in 3-D structures and the scattering-integral method. We verify the 3-D full-wave sensitivity kernels by comparing the predictions from the kernels with the measurements from numerical simulations of wave propagation in models with various small-scale perturbations. In contrast to the 1-D depth sensitivity kernels, our 3-D full-wave kernels exhibit patterns that vary with back azimuths and distances within one wavelength of the receiver, indicating the resolving power not only vertically, and also laterally. In places with dense seismic stations, these kernels will provide a powerful tool to obtain accurate and high-resolution velocity and density models.

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Journal of Geophysical Research: Solid Earth