Effects of Partial Melt in the Uppermost Mantle on SK(K)S Splitting: Global Wavefield Simulations and Potential Applications
Description:
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, dt, of shear-wave splitting (SWS) measurements, provides opportunities to infer constraints on subsurface deformation. However, the limited depth resolution of SK(K)S core-phases, used in investigations of the upper mantle, typically prevents unambiguous assignments on the origin of anisotropy. Even simple SWS patterns may potentially reflect scenarios in which multiple mechanisms (i.e., LPO vs. SPO) or olivine fabric types (e.g., A-, C-, or E-type) 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 splitting parameters can provide enlightening indications on the presence of partial melt. We adapt our model geometries to be applicable to the High Lava Plains in the Cascadia backarc where there is good evidence for the presence of melt in the uppermost mantle. AxiSEM3D is used to compute synthetic seismograms (for both axisymmetric and fully 3D global wavefield simulations) to be able to evaluate effects on SWS measurements for a variety of scenarios, considering different melt configurations (fractions/geometries) and olivine fabric types. Related SWS parameters are obtained by using SplitRacer to measure splitting on the synthetic seismograms over a range of frequencies (up to 0.25 Hz).
Session: Earth’s Structure From the Crust to the Core
Type: Oral
Date: 4/18/2023
Presentation Time: 02:30 PM (local time)
Presenting Author: Eric Loeberich
Student Presenter: No
Invited Presentation:
Authors
Eric Loeberich Presenting Author Corresponding Author eric.loeberich@yale.edu Yale University |
Jonathan Wolf jonathan.wolf@yale.edu Yale University |
Maureen Long maureen.long@yale.edu Yale University |
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Effects of Partial Melt in the Uppermost Mantle on SK(K)S Splitting: Global Wavefield Simulations and Potential Applications
Category
Earth’s Structure From the Crust to the Core