Surface-wave sensitivity to anisotropy in a 3D seismogeodynamics mantle plume model.

Matteo Desiderio , Ana Ferreira, Stephen Paul Hicks , Manuele Faccenda, Francesco Rappisi, Antonio Manjón-Cabeza Córdoba, Maxim Ballmer

High-resolution anisotropic seismic images of the upper mantle provide fundamental constraints on mantle plume dynamics and mantle deformation. Seismic tomography has come far by using travel-time and waveform (phase) information but has exploited amplitude information only to a limited extent.
Here, we calculate adjoint sensitivity kernels to assess the value of incorporating amplitude information and to identify the elastic parameters that most effectively characterise mantle plumes in the uppermost mantle.
We first compute strain-induced mineral fabrics and the resulting full elastic tensor in a realistic 3D mantle plume setting.
Then, full-waveform computations are carried out within this medium to obtain kernels for fundamental-mode Rayleigh- and Love-wave amplitude (and phase) measurements for all the 21 elastic parameters controlling seismic anisotropy.
Finally, we explore the sensitivity of combined observables, such as Rayleigh-wave cross-component phase-delay differences and horizontal/vertical amplitude ratios (i.e., Rayleigh wave ellipticity).
Our gallery of phase and amplitude surface-wave adjoint kernels reveals strong and complex sensitivity of these measurements to shear-wave radial anisotropy and to second- and fourth-degree azimuthal anisotropy parameters.
We further show that amplitude measurements are highly sensitive to the same elastic tensor components as phase measurements, but with distinct spatial sensitivity patterns that complement phase measurements and strengthen constraints in anisotropic tomography inversions.
We find that our combined observables maximize sensitivity beneath and near receivers, highlighting their potential for constraining mantle flow in settings with sparse or logistically challenging instrumentation, such as in oceanic domains.