Observations of Rayleigh and Love wave Azimuthal Anisotropy Across Alaska

Xiongwei Liu, Chuanming Liu, Michael H Ritzwoller

Using ambient noise data from 10 s to 50 s period across Alaska, we confirm previous estimates of Rayleigh wave 2[psi] azimuthal anisotropy and present the first estimates of Rayleigh wave 4[psi] and Love wave 2[psi] and 4[psi] azimuthal anisotropy, where [psi] is the angle of propagation. As in earlier studies, the fast axis orientations of Rayleigh wave 2[psi] are mainly parallel to major faults in Alaska at all periods. We also find that on average the fast axis of Love wave 4[psi] is rotated 45° relative to Rayleigh wave 2[psi], the fast axis of Rayleigh wave 4[psi] aligns with Love wave 2[psi], and the fast axis differences of Rayleigh and Love wave 2[psi] range between 0 and 90 degrees with many between 40 to 60 degrees. These observations are consistent with non-elliptical anisotropy with the ellipticity parameters [eta]! and [eta]" considerably smaller than 1. Observations of Love wave 2[psi] and Rayleigh wave 4[psi] reflect strong Rayleigh-Love coupling, which causes the observed complementary trends with period of the amplitudes of Rayleigh and Love wave 2[psi] and Rayleigh and Love wave 4[psi]. Recent theories of Rayleigh-Love coupling based on a quasi degenerate theory allow these observations to be understood and to be used in the future to improve models of the elastic tensor in the crust and mantle.