No Negative Radial Anisotropy below Cratons: Evidence from Bayesian Inversion


Download Poster here


  • Global radial anisotropic models are inconsistent meaning geological interpretation of active/ancient mantle flow/deformation is challenging.
  • One recent interpretation (Priestley et al., 2020) suggests that negative radial anisotropy in the CAM2016 model at ~150km depth within cratons reflects their formation by horizontal shortening/vertical thickening. This mechanism is not easily reconciled with other available models however.
  • Using variable parameterizations within both LSQR and Bayesian inversions of Rayleigh and Love (R&L) surface wave dispersion curves, we test whether negative radial anisotropy is reliably recovered at upper mantle depths using synthetic models (Section 3) and whether anisotropic anomalies are required below cratons using real data inversions (Section 4).
  • Both algorithmic and parameterization choices affect ‘recovered’ radial anisotropy meaning existing geological interpretations may be biased.
  • Future work involves benchmark inversions for mid-ocean ridges & active mountain belts and a global inversion using the Bayesian algorithm (Soergel et al., in prep).

Take Home Messages

  1. Negative radial anisotropy below cratons (~150km depth) can be reproduced using classical LSQR inversion, but is likely an artefact…
  2. Bayesian inversion with free V parameterization yields no negative radial anisotropy below cratons, only +5-10% Xi above 150km depth similar to PREM.
  3. Craton formation by horizontal shortening (Priestley et al., 2020) is not favourable.
  4. Set VPH free in surface wave inversions, preferably with Bayesian algorithms!