Surface Wave Constraints on The Oceanic Lithosphere-Asthenosphere Boundary
- Author(s): Xing, Zheng
- Advisor(s): Boyce, Caroline D.M.L.
- et al.
The lithosphere-asthenosphere boundary (LAB) is a fundamental concept of plate tectonics
theory but its origin remains elusive. The lithospheric plate thickness and its relation to
crustal age can help better understand the nature of the rheology contrast between the plate
and the underlying asthenosphere. This dissertation discusses resolving oceanic lithosphereasthenosphere
boundary (LAB) using surface waves. It rst talks about an important step
in surface wave tomography - crustal corrections. By studying the eects of using dierent
a priori crust models on the nal mantle structure, we nd out that dierences between
resulting mantle models is small compared to model uncertainty itself obtained using a model
space search method. Secondly, we focus on analyzing dierent seismological proxies for LAB
detection, using three dierent datasets and a model space search approach. The resulting
statistical distributions of possible models allows us to infer the reliability of the velocity and
anisotropy models of the Pacic upper mantle and determine whether the dierences between
the proxies are signicant. We found that the LAB depth constrained by surface wave phase
velocities is associated with large uncertainties for all proxies. Including surface wave group
velocity data aected the radial anisotropy models, but did not satisfactorily reduce the
uncertainties on the LAB depth proxies. We nally compared our LAB depth results with
theoretical predictions from lithosphere cooling models under dierent conditions. It is
shown that a half space cooling model with dehydration eects at the ridge best explains
our models, though there remains signicant uncertainties and dependence on the dataset
that need to be investigated in future work.