Effects of Partial Melt in the Uppermost Mantle on SKS Splitting: Global Wavefield Simulations and potential Applications
Abstract
Observations of seismic anisotropy can be caused by lattice-preferred orientation (LPO) of intrinsically anisotropic minerals such as olivine, or shape-preferred orientation (SPO) of elastically contrasting materials as in the presence of partial melt. A detailed understanding of anisotropy based on the fast polarization direction, φ, and the estimated delay time, δt, provides interesting opportunities to infer subsurface deformation. However, the limited depth resolution of SKS core-phases, often used in investigations of the upper mantle, typically prevents unambiguous assignments on the origin of anisotropy. Even simple shear-wave splitting patterns may potentially reflect a complex depth distribution, and scenarios in which multiple mechanisms (i.e., LPO vs. SPO) or olivine fabric types (e.g., A-, C-, or E-type) might contribute to the observed splitting signal. If partial melt is present in the uppermost mantle, it may affect this signal via two different mechanisms: first, if melt inclusions are aligned through deformation, then SPO may contribute to anisotropy, and second, the partitioning of water into the melt may change the dominant olivine fabric in the surrounding matrix. In this study, we investigate whether the lateral distribution of splitting parameters can provide indications on the presence of partial melt. We use AxiSEM3D to compute synthetic seismograms (for both axisymmetric and fully 3D global wavefield simulations) to evaluate the potential effects of melt in the uppermost mantle on measurements of seismic anisotropy. A variety of scenarios are tested, incorporating different melt geometries and olivine fabric types into our input models. SKS splitting parameters are obtained by using SplitRacer to measure splitting on the synthetic seismograms over a range of frequencies (up to 0.25 Hz). We adapt our model geometries to be applicable to several regions where there is good evidence for the presence of partial melt in the uppermost mantle, including the High Lava Plains in the Cascadia backarc and the Central Appalachian Anomaly in the eastern United States.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMDI15B0014L