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Surface Wave Constraints on The Oceanic Lithosphere-Asthenosphere Boundary

  • Author(s): Xing, Zheng
  • Advisor(s): Boyce, Caroline D.M.L.
  • et al.
Abstract

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.

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