Effect of the Coriolis Force on Body Wave Polarization Anomalies Inferred From 3D Wave Simulations

Polarization of P and S waves (the orientation of the radial and transverse component energy) are commonly used in a variety of teleseismic methods to better constrain properties of Earths mantle and crust and core-mantle boundary topography. Additionally, many body wave studies rely on consistent and predictable polarizations of teleseismic body waves (e.g., shear wave splitting, misalignment of seismometers, receiver functions). However, we investigate how some polarization anomalies of shear waves (those that deviate from the predicted polarization) can be explained by nonstructural effects, such as the Earths Coriolis force, multiple phase arrivals, and source effects. We use numerical modeling of earthquakes and explosive sources with 1D and 3D Earth models (GLAD-M15/25: Bozdag et al, 2016, Lei et al., 2020; S40RTS: Ritsema et al., 2011) with the global wave propagation solver SPECFEM3D_GLOBE (Komatitsch & Tromp, 2002). We show that Earth's rotation can produce polarization changes on mantle shear waves up to 7 degrees and on core phases up to 3 degrees. Source effects can introduce additional polarization anomalies, where the collective impact of these effects can produce SKS polarizations to deviate up to 5 degrees and SKKS up to 10 degrees from the radial direction. Uncorrected polarizations could produce measurement error on mantle anisotropy estimates derived from shear wave splitting, incorrect station misalignment, and inaccurate estimates of Earth structure and topography. We also show how to correct for Earth's rotation on teleseismic shear waves using ray tracing. However, we recommend the use of numerical simulations with a rotating Earth to fully and accurately account for the Coriolis effect, source effects, and multiple phase arrivals on the polarizations of shear waves.