Intrinsic versus extrinsic seismic anisotropy: The radial anisotropy in reference Earth models

Abstract Seismic anisotropy usually arises from different mechanisms, which include lattice or crystallographic preferred orientation (LPO, CPO), alignment of cracks with or without fluid inclusions, fine layering, or partial melting. This makes the interpretation of anisotropy in terms of “intrinsic” (produced by LPO, CPO) versus “extrinsic” (produced by other mechanisms) properties difficult and nonunique. The radial anisotropy in the one‐dimensional, global spherically symmetric reference Earth is usually claimed to be intrinsic. Here we explore whether the radial anisotropy in one‐dimensional reference Earth models including preliminary reference Earth model (PREM) and the constrained reference Earth model ACY400 contains extrinsic anisotropy, especially in relation to fine layering. We conclude that as well as intrinsic anisotropy, extrinsic anisotropy introduced by finely layered models, can be considered to explain the lithospheric anisotropy in PREM, but cannot explain alone its asthenospheric anisotropy. We also find that radial anisotropy in model ACY400 is mainly intrinsic due to its petrological constraints.