iPlex Lunch spring-2017

1. Transdimensional approach applied to the measurement of higher mode surface wave (Haotian Xu)

The analysis of higher mode surface wave carries unique, independent constraints on the structure at depth and thus enhance resolution in the deep upper mantle, transition zone, and uppermost lower mantle. However, direct measurement of higher modes is challenging because their group velocities overlap significantly in a long frequency range. We developed a new non-linear waveform inversion technique using a transdimensional Bayesian approach to measure path-specific multimode Rayleigh wave dispersion. Fundamental mode, overtones as well as their uncertainties can be measured by this method. We applied our method to both synthetic and real data and reasonable results were obtained, demonstrating the feasibility of this method.

2. Assessing the Depth of the Pacific Lithosphere-Asthenosphere Boundary From Various Proxies With a Bayesian Approach (Zheng Xing)

Determining how the lithosphere-asthenosphere boundary (LAB) depth changes with ocean age is one of the keys to understanding the origin of oceanic plates. Previous studies have shown that inversion of surface wave dispersion curves for S-wave velocities yields LAB depth based on VS increase that depends on oceanic crustal age, consistent with thermal effects. However, depth changes in radial anisotropy used as LAB depth proxy do not display any age dependence. Although this could mean that the two proxies highlight different processes in the formation and evolution of oceanic plates (e.g. Hansen et al., 2016), the non-uniqueness of the inverse problem questions whether these two proxies are really seeing different rock properties. Here, we applied a model space search approach to two different datasets of surface wave phase velocity data to get an more quantitative analysis on uncertainties of the two LAB depth proxies.